PyNaCl: Python binding to the libsodium library¶

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PyNaCl is a Python binding to libsodium, which is a fork of the Networking and Cryptography library. These libraries have a stated goal of improving usability, security and speed. It supports Python 2.7 and 3.4+ as well as PyPy 2.6+.

Features¶

Digital signatures
Secret-key encryption
Public-key encryption
Hashing and message authentication
Password based key derivation and password hashing

Contents¶

Public Key Encryption¶

Imagine Alice wants something valuable shipped to her. Because it’s valuable, she wants to make sure it arrives securely (i.e. hasn’t been opened or tampered with) and that it’s not a forgery (i.e. it’s actually from the sender she’s expecting it to be from and nobody’s pulling the old switcheroo).

One way she can do this is by providing the sender (let’s call him Bob) with a high-security box of her choosing. She provides Bob with this box, and something else: a padlock, but a padlock without a key. Alice is keeping that key all to herself. Bob can put items in the box then put the padlock onto it. But once the padlock snaps shut, the box cannot be opened by anyone who doesn’t have Alice’s private key.

Here’s the twist though: Bob also puts a padlock onto the box. This padlock uses a key Bob has published to the world, such that if you have one of Bob’s keys, you know a box came from him because Bob’s keys will open Bob’s padlocks (let’s imagine a world where padlocks cannot be forged even if you know the key). Bob then sends the box to Alice.

In order for Alice to open the box, she needs two keys: her private key that opens her own padlock, and Bob’s well-known key. If Bob’s key doesn’t open the second padlock, then Alice knows that this is not the box she was expecting from Bob, it’s a forgery.

This bidirectional guarantee around identity is known as mutual authentication.

Examples¶

nacl.public.Box¶

The Box class uses the given public and private (secret) keys to derive a shared key, which is used with the nonce given to encrypt the given messages and to decrypt the given ciphertexts. The same shared key will be generated from both pairing of keys, so given two keypairs belonging to Alice (pkalice, skalice) and Bob (pkbob, skbob), the key derived from (pkalice, skbob) will equal that from (pkbob, skalice).

This is how the system works:

import nacl.utils
from nacl.public import PrivateKey, Box

# Generate Bob's private key, which must be kept secret
skbob = PrivateKey.generate()

# Bob's public key can be given to anyone wishing to send
#   Bob an encrypted message
pkbob = skbob.public_key

# Alice does the same and then Alice and Bob exchange public keys
skalice = PrivateKey.generate()
pkalice = skalice.public_key

# Bob wishes to send Alice an encrypted message so Bob must make a Box with
#   his private key and Alice's public key
bob_box = Box(skbob, pkalice)

# This is our message to send, it must be a bytestring as Box will treat it
#   as just a binary blob of data.
message = b"Kill all humans"

PyNaCl can automatically generate a random nonce for us, making the encryption very simple:

# Encrypt our message, it will be exactly 40 bytes longer than the
#   original message as it stores authentication information and the
#   nonce alongside it.
encrypted = bob_box.encrypt(message)

However, if we need to use an explicit nonce, it can be passed along with the message:

# This is a nonce, it *MUST* only be used once, but it is not considered
#   secret and can be transmitted or stored alongside the ciphertext. A
#   good source of nonces are just sequences of 24 random bytes.
nonce = nacl.utils.random(Box.NONCE_SIZE)

encrypted = bob_box.encrypt(message, nonce)

Finally, the message is decrypted (regardless of how the nonce was generated):

# Alice creates a second box with her private key to decrypt the message
alice_box = Box(skalice, pkbob)

# Decrypt our message, an exception will be raised if the encryption was
#   tampered with or there was otherwise an error.
plaintext = alice_box.decrypt(encrypted)

nacl.public.SealedBox¶

The SealedBox class encrypts messages addressed to a specified key-pair by using ephemeral sender’s keypairs, which will be discarded just after encrypting a single plaintext message.

This kind of construction allows sending messages, which only the recipient can decrypt without providing any kind of cryptographic proof of sender’s authorship.

Warning

By design, the recipient will have no means to trace the ciphertext to a known author, since the sending keypair itself is not bound to any sender’s identity, and the sender herself will not be able to decrypt the ciphertext she just created, since the private part of the key cannot be recovered after use.

This is how the system works:

import nacl.utils
from nacl.public import PrivateKey, SealedBox

# Generate Bob's private key, as we've done in the Box example
skbob = PrivateKey.generate()
pkbob = skbob.public_key

# Alice wishes to send a encrypted message to Bob,
# but prefers the message to be untraceable
sealed_box = SealedBox(pkbob)

# This is Alice's message
message = b"Kill all kittens"

# Encrypt the message, it will carry the ephemeral key public part
# to let Bob decrypt it
encrypted = sealed_box.encrypt(message)

Now, Bob wants to read the secret message he just received; therefore he must create a SealedBox using his own private key:

unseal_box = SealedBox(skbob)
# decrypt the received message
plaintext = unseal_box.decrypt(encrypted)

Reference¶

class nacl.public.PublicKey(public_key, encoder)[source]¶

The public key counterpart to an Curve25519 PrivateKey for encrypting messages.

Parameters:	public_key (bytes) – Encoded Curve25519 public key. encoder – A class that is able to decode the `public_key`.

class nacl.public.PrivateKey(private_key, encoder)[source]¶

Private key for decrypting messages using the Curve25519 algorithm.

Warning

This must be protected and remain secret. Anyone who knows the value of your PrivateKey can decrypt any message encrypted by the corresponding PublicKey

Parameters:	private_key (bytes) – The private key used to decrypt messages. encoder – A class that is able to decode the `private_key`.

public_key¶: An instance of PublicKey that corresponds with the private key.

classmethod generate()[source]¶

Generates a random PrivateKey object

Returns:	An instance of `PrivateKey`.

class nacl.public.Box(private_key, public_key)[source]¶

The Box class boxes and unboxes messages between a pair of keys

The ciphertexts generated by Box include a 16 byte authenticator which is checked as part of the decryption. An invalid authenticator will cause the decrypt function to raise an exception. The authenticator is not a signature. Once you’ve decrypted the message you’ve demonstrated the ability to create arbitrary valid message, so messages you send are repudiable. For non-repudiable messages, sign them after encryption.

Parameters:	private_key – An instance of `PrivateKey` used to encrypt and decrypt messages public_key – An instance of `PublicKey` used to encrypt and decrypt messages

classmethod decode(encoded, encoder)[source]¶

Decodes a serialized Box.

Returns:	An instance of `Box`.

encrypt(plaintext, nonce, encoder)[source]¶

Encrypts the plaintext message using the given nonce (or generates one randomly if omitted) and returns the ciphertext encoded with the encoder.

Warning

It is VITALLY important that the nonce is a nonce, i.e. it is a number used only once for any given key. If you fail to do this, you compromise the privacy of the messages encrypted.

Parameters:	plaintext (bytes) – The plaintext message to encrypt. nonce (bytes) – The nonce to use in the encryption. encoder – A class that is able to decode the ciphertext.
Returns:	An instance of `EncryptedMessage`.

decrypt(ciphertext, nonce, encoder)[source]¶

Decrypts the ciphertext using the nonce (explicitly, when passed as a parameter or implicitly, when omitted, as part of the ciphertext) and returns the plaintext message.

Parameters:	ciphertext (bytes) – The encrypted message to decrypt. nonce (bytes) – The nonce to use in the decryption. encoder – A class that is able to decode the plaintext.
Return bytes:	The decrypted plaintext.

shared_key()[source]¶

Returns the Curve25519 shared secret, that can then be used as a key in other symmetric ciphers.

Warning

It is VITALLY important that you use a nonce with your symmetric cipher. If you fail to do this, you compromise the privacy of the messages encrypted. Ensure that the key length of your cipher is 32 bytes.

Return bytes:	The shared secret.

class nacl.public.SealedBox(receiver_key)[source]¶

The SealedBox class can box and unbox messages sent to a receiver key using an ephemeral sending keypair.

encrypt(plaintext, encoder)[source]¶

Encrypt the message using a Box constructed from an ephemeral key-pair and the receiver key.

The public part of the ephemeral key-pair will be enclosed in the returned ciphertext.

The private part of the ephemeral key-pair will be scrubbed before returning the ciphertext, therefore, the sender will not be able to decrypt the message.

Parameters:	plaintext (bytes) – The plaintext message to encrypt. encoder – A class that is able to decode the ciphertext.
Return bytes:	The public part of the ephemeral keypair, followed by the encrypted ciphertext

decrypt(ciphertext, encoder)[source]¶

Decrypt the message using a Box constructed from the receiver key and the ephemeral key enclosed in the ciphertext.

Parameters:	ciphertext (bytes) – The ciphertext message to decrypt. encoder – A class that is able to decode the ciphertext.
Return bytes:	The decrypted message

Algorithm¶

Public Keys: Curve25519 high-speed elliptic curve cryptography

Secret Key Encryption¶

Secret key encryption (also called symmetric key encryption) is analogous to a safe. You can store something secret through it and anyone who has the key can open it and view the contents. SecretBox functions as just such a safe, and like any good safe any attempts to tamper with the contents is easily detected.

Secret key encryption allows you to store or transmit data over insecure channels without leaking the contents of that message, nor anything about it other than the length.

Example¶

import nacl.secret
import nacl.utils

# This must be kept secret, this is the combination to your safe
key = nacl.utils.random(nacl.secret.SecretBox.KEY_SIZE)

# This is your safe, you can use it to encrypt or decrypt messages
box = nacl.secret.SecretBox(key)

# This is our message to send, it must be a bytestring as SecretBox will
#   treat it as just a binary blob of data.
message = b"The president will be exiting through the lower levels"

PyNaCl can automatically generate a random nonce for us, making the encryption very simple:

# Encrypt our message, it will be exactly 40 bytes longer than the
#   original message as it stores authentication information and the
#   nonce alongside it.
encrypted = box.encrypt(message)

However, if we need to use an explicit nonce, it can be passed along with the message:

# This is a nonce, it *MUST* only be used once, but it is not considered
#   secret and can be transmitted or stored alongside the ciphertext. A
#   good source of nonces are just sequences of 24 random bytes.
nonce = nacl.utils.random(nacl.secret.SecretBox.NONCE_SIZE)

encrypted = box.encrypt(message, nonce)

Finally, the message is decrypted (regardless of how the nonce was generated):

# Decrypt our message, an exception will be raised if the encryption was
#   tampered with or there was otherwise an error.
plaintext = box.decrypt(encrypted)

Requirements¶

Key¶

The 32 bytes key given to SecretBox must be kept secret. It is the combination to your “safe” and anyone with this key will be able to decrypt the data, or encrypt new data.

Nonce¶

The 24-byte nonce (Number used once) given to encrypt() and decrypt() must NEVER be reused for a particular key. Reusing a nonce may give an attacker enough information to decrypt or forge other messages. A nonce is not considered secret and may be freely transmitted or stored in plaintext alongside the ciphertext.

A nonce does not need to be random or unpredictable, nor does the method of generating them need to be secret. A nonce could simply be a counter incremented with each message encrypted, which can be useful in connection-oriented protocols to reject duplicate messages (“replay attacks”). A bidirectional connection could use the same key for both directions, as long as their nonces never overlap (e.g. one direction always sets the high bit to “1”, the other always sets it to “0”).

If you use a counter-based nonce along with a key that is persisted from one session to another (e.g. saved to disk), you must store the counter along with the key, to avoid accidental nonce reuse on the next session. For this reason, many protocols derive a new key for each session, reset the counter to zero with each new key, and never store the derived key or the counter.

You can safely generate random nonces by calling random() with SecretBox.NONCE_SIZE.

Reference¶

class nacl.secret.SecretBox(key, encoder)[source]¶

The SecretBox class encrypts and decrypts messages using the given secret key.

The ciphertexts generated by Secretbox include a 16 byte authenticator which is checked as part of the decryption. An invalid authenticator will cause the decrypt function to raise an exception. The authenticator is not a signature. Once you’ve decrypted the message you’ve demonstrated the ability to create arbitrary valid message, so messages you send are repudiable. For non-repudiable messages, sign them after encryption.

Parameters:	key (bytes) – The secret key used to encrypt and decrypt messages. encoder – A class that is able to decode the `key`.

encrypt(plaintext, nonce, encoder)[source]¶

Encrypts the plaintext message using the given nonce (or generates one randomly if omitted) and returns the ciphertext encoded with the encoder.

Warning

It is VITALLY important that the nonce is a nonce, i.e. it is a number used only once for any given key. If you fail to do this, you compromise the privacy of the messages encrypted. Give your nonces a different prefix, or have one side use an odd counter and one an even counter. Just make sure they are different.

Parameters:	plaintext (bytes) – The plaintext message to encrypt. nonce (bytes) – The nonce to use in the encryption. encoder – A class that is able to decode the ciphertext.
Returns:	An instance of `EncryptedMessage`.

decrypt(ciphertext, nonce, encoder)[source]¶

Decrypts the ciphertext using the nonce (explicitly, when passed as a parameter or implicitly, when omitted, as part of the ciphertext) and returns the plaintext message.

Parameters:	ciphertext (bytes) – The encrypted message to decrypt. nonce (bytes) – The nonce to use in the decryption. encoder – A class that is able to decode the plaintext.
Return bytes:	The decrypted plaintext.

Algorithm details¶

Encryption:	Salsa20 stream cipher
Authentication:	Poly1305 MAC

Digital Signatures¶

You can use a digital signature for many of the same reasons that you might sign a paper document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender such that they cannot deny sending it (authentication and non-repudiation) and that the message was not altered in transit (integrity).

Digital signatures allow you to publish a public key, and then you can use your private signing key to sign messages. Others who have your public key can then use it to validate that your messages are actually authentic.

Example¶

Signer’s perspective (SigningKey)

import nacl.encoding
import nacl.signing

# Generate a new random signing key
signing_key = nacl.signing.SigningKey.generate()

# Sign a message with the signing key
signed = signing_key.sign(b"Attack at Dawn")

# Obtain the verify key for a given signing key
verify_key = signing_key.verify_key

# Serialize the verify key to send it to a third party
verify_key_hex = verify_key.encode(encoder=nacl.encoding.HexEncoder)

Verifier’s perspective (VerifyKey)

import nacl.signing

# Create a VerifyKey object from a hex serialized public key
verify_key = nacl.signing.VerifyKey(verify_key_hex, encoder=nacl.encoding.HexEncoder)

# Check the validity of a message's signature
# Will raise nacl.exceptions.BadSignatureError if the signature check fails
verify_key.verify(signed)

Reference¶

class nacl.signing.SigningKey(seed, encoder)[source]¶

Private key for producing digital signatures using the Ed25519 algorithm.

Signing keys are produced from a 32-byte (256-bit) random seed value. This value can be passed into the SigningKey as a bytes() whose length is 32.

Warning

This must be protected and remain secret. Anyone who knows the value of your SigningKey or its seed can masquerade as you.

Parameters:	seed (bytes) – Random 32-byte value (i.e. private key). encoder – A class that is able to decode the `seed`.

verify_key¶: An instance of VerifyKey (i.e. public key) that corresponds with the signing key.

classmethod generate()[source]¶

Generates a random SigningKey object

Returns:	An instance of `SigningKey`.

sign(message, encoder)[source]¶

Sign a message using this key.

Parameters:	message (bytes) – The data to be signed. encoder – A class that is able to decode the signed message.
Returns:	An instance of `SignedMessage`.

class nacl.signing.VerifyKey(key, encoder)[source]¶

The public key counterpart to an Ed25519 SigningKey for producing digital signatures.

Parameters:	key (bytes) – A serialized Ed25519 public key. encoder – A class that is able to decode the `key`.

verify(smessage, signature, encoder)[source]¶

Verifies the signature of a signed message.

Parameters:	smessage (bytes) – The signed message to verify. This is either the original message or the concated signature and message. signature (bytes) – The signature of the message to verify against. If the value of `smessage` is the concated signature and message, this parameter can be `None`. encoder – A class that is able to decode the secret message and signature.
Return bytes:	The message if successfully verified.
Raises:	nacl.exceptions.BadSignatureError – This is raised if the signature is invalid.

class nacl.signing.SignedMessage[source]¶

A bytes subclass that holds a messaged that has been signed by a SigningKey.

signature¶: The signature contained within the SignedMessage.

message¶: The message contained within the SignedMessage.

Ed25519¶

Ed25519 is a public-key signature system with several attractive features:

Fast single-signature verification: Ed25519 takes only 273364 cycles to verify a signature on Intel’s widely deployed Nehalem/Westmere lines of CPUs. (This performance measurement is for short messages; for very long messages, verification time is dominated by hashing time.) Nehalem and Westmere include all Core i7, i5, and i3 CPUs released between 2008 and 2010, and most Xeon CPUs released in the same period.
Even faster batch verification: Ed25519 performs a batch of 64 separate signature verifications (verifying 64 signatures of 64 messages under 64 public keys) in only 8.55 million cycles, i.e., under 134000 cycles per signature. Ed25519 fits easily into L1 cache, so contention between cores is negligible: a quad-core 2.4GHz Westmere verifies 71000 signatures per second, while keeping the maximum verification latency below 4 milliseconds.
Very fast signing: Ed25519 takes only 87548 cycles to sign a message. A quad-core 2.4GHz Westmere signs 109000 messages per second.
Fast key generation: Key generation is almost as fast as signing. There is a slight penalty for key generation to obtain a secure random number from the operating system; /dev/urandom under Linux costs about 6000 cycles.
High security level: This system has a 2^128 security target; breaking it has similar difficulty to breaking NIST P-256, RSA with ~3000-bit keys, strong 128-bit block ciphers, etc. The best attacks known actually cost more than 2^140 bit operations on average, and degrade quadratically in success probability as the number of bit operations drops.
Collision resilience: Hash-function collisions do not break this system. This adds a layer of defense against the possibility of weakness in the selected hash function.
No secret array indices: Ed25519 never reads or writes data from secret addresses in RAM; the pattern of addresses is completely predictable. Ed25519 is therefore immune to cache-timing attacks, hyperthreading attacks, and other side-channel attacks that rely on leakage of addresses through the CPU cache.
No secret branch conditions: Ed25519 never performs conditional branches based on secret data; the pattern of jumps is completely predictable. Ed25519 is therefore immune to side-channel attacks that rely on leakage of information through the branch-prediction unit.
Small signatures: Ed25519 signatures are only 512-bits (64 bytes), one of the smallest signature sizes available.
Small keys: Ed25519 keys are only 256-bits (32 bytes), making them small enough to easily copy and paste. Ed25519 also allows the public key to be derived from the private key, meaning that it doesn’t need to be included in a serialized private key in cases you want both.
Deterministic: Unlike (EC)DSA, Ed25519 does not rely on an entropy source when signing messages (which has lead to catastrophic private key compromises), but instead computes signature nonces from a combination of a hash of the signing key’s “seed” and the message to be signed. This avoids using an entropy source for nonces, which can be a potential attack vector if the entropy source is not generating good random numbers. Even a single reused nonce can lead to a complete disclosure of the private key in these schemes, which Ed25519 avoids entirely by being deterministic instead of tied to an entropy source.

The numbers 87548 and 273364 shown above are official eBATS reports for a Westmere CPU (Intel Xeon E5620, hydra2).

Ed25519 signatures are elliptic-curve signatures, carefully engineered at several levels of design and implementation to achieve very high speeds without compromising security.

Algorithm¶

Signatures: Ed25519 digital signature system

k:	Ed25519 private key (passed into `SigningKey`)
A:	Ed25519 public key derived from k
M:	message to be signed
R:	a deterministic nonce value calculated from a combination of private key data RH and the message M
S:	Ed25519 signature

Hashing¶

Cryptographic secure hash functions are irreversible transforms of input data to a fixed length digest.

The standard properties of a cryptographic hash make these functions useful both for standalone usage as data integrity checkers, as well as black-box building blocks of other kind of algorithms and data structures.

All of the hash functions exposed in nacl.hash can be used as data integrity checkers.

Integrity check examples¶

Message’s creator perspective (sha256(),: sha512(), blake2b())

import nacl.encoding
import nacl.hash

HASHER = nacl.hash.sha256
# could be nacl.hash.sha512 or nacl.hash.blake2b instead

# define a 1024 bytes log message
msg = 16*b'256 BytesMessage'
digest = HASHER(msg, encoder=nacl.encoding.HexEncoder)

# now send msg and digest to the user
print(nacl.encoding.HexEncoder.encode(msg))
print(digest)

Message’s user perspective (sha256(),: sha512(), blake2b())

from nacl.bindings.utils import sodium_memcmp
import nacl.encoding
import nacl.hash

HASHER = nacl.hash.sha256
# could be nacl.hash.sha512 or nacl.hash.blake2b instead

# we received a 1024 bytes long message and it hex encoded digest
received_msg = nacl.encoding.HexEncoder.decode(
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
b'3235362042797465734d6573736167653235362042797465734d657373616765'
)

dgst = b'12b413c70c148d79bb57a1542156c5f35e24ad77c38e8c0e776d055e827cdd45'

shortened = received_msg[:-1]
modified = b'modified' + received_msg[:-8]

orig_dgs = HASHER(received_msg, encoder=nacl.encoding.HexEncoder)
shrt_dgs = HASHER(shortened, encoder=nacl.encoding.HexEncoder)
mdfd_dgs = HASHER(modified, encoder=nacl.encoding.HexEncoder)

def eq_chk(dgs0, dgs1):
    if sodium_memcmp(dgs0, dgs1):
        return 'equals'
    return 'is different from'

MSG = 'Digest of {0} message {1} original digest'

for chk in (('original', orig_dgs),
            ('truncated', shrt_dgs),
            ('modified', mdfd_dgs)):

    print(MSG.format(chk[0], eq_chk(dgst, chk[1])))

Additional hashing usages for `blake2b`¶

As already hinted above, traditional cryptographic hash functions can be used as building blocks for other uses, typically combining a secret-key with the message via some construct like the HMAC one.

The blake2b hash function can be used directly both for message authentication and key derivation, replacing the HMAC construct and the HKDF one by setting the additional parameters key, salt and person.

Please note that key stretching procedures like HKDF or the one outlined in Key derivation are not suited to derive a cryptographically-strong key from a low-entropy input like a plain-text password or to compute a strong long-term stored hash used as password verifier. See the Password hashing section for some more informations and usage examples of the password hashing constructs provided in pwhash.

Message authentication¶

To authenticate a message, using a secret key, the blake2b function must be called as in the following example.

Message authentication example¶

import nacl.encoding
from nacl.hash import blake2b

msg = 16*b'256 BytesMessage'
msg2 = 16*b'256 bytesMessage'

auth_key = nacl.utils.random(size=64)
# the simplest way to get a cryptographic quality auth_key
# is to generate it with a cryptographic quality
# random number generator

auth1_key = nacl.utils.random(size=64)
# generate a different key, just to show the mac is changed
# both with changing messages and with changing keys

mac0 = blake2b(msg, key=auth_key, encoder=nacl.encoding.HexEncoder)
mac1 = blake2b(msg, key=auth1_key, encoder=nacl.encoding.HexEncoder)
mac2 = blake2b(msg2, key=auth_key, encoder=nacl.encoding.HexEncoder)

for i, mac in enumerate((mac0, mac1, mac2)):
    print('Mac{0} is: {1}.'.format(i, mac))

Key derivation¶

The blake2b algorithm can replace a key derivation function by following the lines of:

Key derivation example¶

import nacl.encoding
import nacl.utils
from nacl.hash import blake2b

master_key = nacl.utils.random(64)

derivation_salt = nacl.utils.random(16)

personalization = b'<DK usage>'

derived = blake2b(b'', key=master_key, salt=derivation_salt,
                  personal=personalization,
                  encoding=nacl.encoding.RawEncoder)

By repeating the key derivation procedure before encrypting our messages, and sending the derivation_salt along with the encrypted message, we can expect to never reuse a key, drastically reducing the risks which ensue from such a reuse.

Password hashing¶

Password hashing and password based key derivation mechanisms in actual use are all based on the idea of iterating a hash function many times on a combination of the password and a random salt, which is stored along with the hash, and allows verifying a proposed password while avoiding clear-text storage.

The latest developments in password hashing have been memory-hard and tunable mechanisms, pioneered by scrypt [SD2012], and followed-on by the schemes submitted to the Password Hashing Competition [PHC].

The nacl.pwhash module exposes both the PHC recommended partially data dependent argon2id and the data independent argon2i mechanisms alongside to the scrypt one.

In the case of password storage, it’s usually suggested to give preference to data dependent mechanisms, therefore the default mechanism suggested by libsodium since version 1.0.15, and therefore by PyNaCl since version 1.2 is argon2id.

If you think in your use-case the risk of potential timing-attacks stemming from data-dependency is greater than the potential time/memory trade-offs stemming out of data-independency, you should prefer argon2i to argon2id or scrypt

Hashers and parameters¶

PyNaCl exposes the functions and the associated parameters needed to exploit the password hashing constructions in a uniform way in the modules argon2id, argon2i and scrypt, therefore, if you need to change your choice of construction, you simply need to replace one module name with another in the example below.

Further, if you just want to use a default choosen construction, you can directly call nacl.pwhash.str() or nacl.pwhash.kdf() to use the preferred construct in modular crypt password hashing or key derivation mode.

Password storage and verification¶

All implementations of the modular crypt hasher str function internally generate a random salt, and return a hash encoded in ascii modular crypt format, which can be stored in a shadow-like file

To verify a user-proposed password, the verify() function checks the stored hash prefix, and dispatches verification to the correct checker, which in turn extracts the used salt, memory and operation count parameters from the modular format string and checks the compliance of the proposed password with the stored hash

Key derivation¶

Alice needs to send a secret message to Bob, using a shared password to protect the content. She generates a random salt, combines it with the password using one of the kdf functions and sends the message along with the salt and key derivation parameters.

from nacl import pwhash, secret, utils


password = b'password shared between Alice and Bob'
message = b"This is a message for Bob's eyes only"

kdf = pwhash.argon2i.kdf
salt = utils.random(pwhash.argon2i.SALTBYTES)
ops = pwhash.argon2i.OPSLIMIT_SENSITIVE
mem = pwhash.argon2i.MEMLIMIT_SENSITIVE

# or, if there is a need to use scrypt:
# kdf = pwhash.scrypt.kdf
# salt = utils.random(pwhash.scrypt.SALTBYTES)
# ops = pwhash.scrypt.OPSLIMIT_SENSITIVE
# mem = pwhash.scrypt.MEMLIMIT_SENSITIVE

Alices_key = kdf(secret.SecretBox.KEY_SIZE, password, salt,
                 opslimit=ops, memlimit=mem)
Alices_box = secret.SecretBox(Alices_key)
nonce = utils.random(secret.SecretBox.NONCE_SIZE)

encrypted = Alices_box.encrypt(message, nonce)

# now Alice must send to Bob both the encrypted message
# and the KDF parameters: salt, opslimit and memlimit;
# using the same kdf mechanism, parameters **and password**
# Bob is able to derive the correct key to decrypt the message


Bobs_key = kdf(secret.SecretBox.KEY_SIZE, password, salt,
               opslimit=ops, memlimit=mem)
Bobs_box = secret.SecretBox(Bobs_key)
received = Bobs_box.decrypt(encrypted)
print(received.decode('utf-8'))

This is a message for Bob's eyes only

if Eve manages to get the encrypted message, and tries to decrypt it with a incorrect password, even if she does know all of the key derivation parameters, she would derive a different key. Therefore the decryption would fail and an exception would be raised

Contrary to the hashed password storage case where a serialization format is well-defined, in the raw key derivation case the library user must take care to store (and retrieve) both a reference to the kdf used to derive the secret key and all the derivation parameters. These parameters are needed to later generate the same secret key from the password.

Module level constants for operation and memory cost tweaking¶

To help in selecting the correct values for the tweaking parameters for the used construction, all the implementation modules provide suggested values for the opslimit and memlimit parameters with the names:

OPSLIMIT_INTERACTIVE

MEMLIMIT_INTERACTIVE

OPSLIMIT_SENSITIVE

MEMLIMIT_SENSITIVE

OPSLIMIT_MODERATE

MEMLIMIT_MODERATE

and the corresponding minimum and maximum allowed values in:

OPSLIMIT_MIN

MEMLIMIT_MIN

OPSLIMIT_MAX

MEMLIMIT_MAX

Further, for each construction, pwhash modules expose the following constants:

STRPREFIX

PWHASH_SIZE

SALTBYTES

BYTES_MIN

BYTES_MAX

In general, the _INTERACTIVE values are recommended in the case of hashes stored for interactive password checking, and lead to a sub-second password verification time, with a memory consumption in the tens of megabytes range, while the _SENSITIVE values are meant to store hashes for password protecting sensitive data, and lead to hashing times exceeding one second, with memory consumption in the hundred of megabytes range. The _MODERATE values, suggested for argon2 mechanisms are meant to run the construct at a runtime and memory cost intermediate between _INTERACTIVE and _SENSITIVE.

[SD2012]

A nice overview of password hashing history is available in Solar Designer’s presentation Password security: past, present, future

[PHC]

The Argon2 recommendation is prominently shown in the Password Hashing Competition site, along to the special recognition shortlist and the original call for submissions.

Support Features¶

Encoders¶

PyNaCl supports a simple method of encoding and decoding messages in different formats. Encoders are simple classes with staticmethods that encode/decode and are typically passed as a keyword argument encoder to various methods.

For example you can generate a signing key and encode it in hex with:

hex_key = nacl.signing.SigningKey.generate().encode(encoder=nacl.encoding.HexEncoder)

Then you can later decode it from hex:

signing_key = nacl.signing.SigningKey(hex_key, encoder=nacl.encoding.HexEncoder)

Built in Encoders¶

class nacl.encoding.RawEncoder[source]¶

class nacl.encoding.HexEncoder[source]¶

class nacl.encoding.Base16Encoder[source]¶

class nacl.encoding.Base32Encoder[source]¶

class nacl.encoding.Base64Encoder[source]¶

class nacl.encoding.URLSafeBase64Encoder[source]¶

Defining your own Encoder¶

Defining your own encoder is easy. Each encoder is simply a class with 2 static methods. For example here is the hex encoder:

import binascii

class HexEncoder(object):

    @staticmethod
    def encode(data):
        return binascii.hexlify(data)

    @staticmethod
    def decode(data):
        return binascii.unhexlify(data)

Exceptions¶

All of the exceptions raised from PyNaCl-exposed methods/functions are subclasses of nacl.exceptions.CryptoError. This means downstream users can just wrap cryptographic operations inside a

try:
    # cryptographic operations
except nacl.exceptions.CryptoError:
    # cleanup after any kind of exception
    # raised from cryptographic-related operations

These are the exceptions implemented in nacl.exceptions:

PyNaCl specific exceptions¶

class CryptoError¶: Base exception for all nacl related errors

class BadSignatureError¶: Raised when the signature was forged or otherwise corrupt.

class InvalidkeyError¶: Raised on password/key verification mismatch

PyNaCl exceptions mixing-in standard library ones¶

Both for clarity and for compatibility with previous releases of the PyNaCl, the following exceptions mix-in the same-named standard library exception to CryptoError.

class RuntimeError¶: is a subclass of both CryptoError and standard library’s RuntimeError, raised for internal library errors

class AssertionError¶: is a subclass of both CryptoError and standard library’s AssertionError, raised by default from ensure() when the checked condition is False

class TypeError¶: is a subclass of both CryptoError and standard library’s TypeError

class ValueError¶: is a subclass of both CryptoError and standard library’s ValueError

Utilities¶

class nacl.utils.EncryptedMessage[source]¶

A bytes subclass that holds a message that has been encrypted by a SecretBox or Box. The full content of the bytes object is the combined nonce and ciphertext.

nonce¶: The nonce used during the encryption of the EncryptedMessage.

ciphertext¶: The ciphertext contained within the EncryptedMessage.

nacl.utils.random(size=32)[source]¶

Returns a random bytestring with the given size.

Parameters:	size (bytes) – The size of the random bytestring.
Return bytes:	The random bytestring.

nacl.utils.ensure(cond, *args, raising=nacl.exceptions.AssertionError)¶

Returns if a condition is true, otherwise raise a caller-configurable Exception

Parameters:	cond (bool) – the condition to be checked args (sequence) – the arguments to be passed to the exception’s constructor raising (exception) – the exception to be raised if cond is False

nacl.hash¶

nacl.hash.sha256(message, encoder)[source]¶

Hashes message with SHA256.

Parameters:	message (bytes) – The message to hash. encoder – A class that is able to encode the hashed message.
Return bytes:	The hashed message.

nacl.hash.sha512(message, encoder)[source]¶

Hashes message with SHA512.

Parameters:	message (bytes) – The message to hash. encoder – A class that is able to encode the hashed message.
Return bytes:	The hashed message.

nacl.hash.blake2b(data, digest_size=BLAKE2B_BYTES, key=b'', salt=b'', person=b'', encoder=nacl.encoding.HexEncoder)[source]¶

One-shot blake2b digest

Parameters:	data (bytes) – the digest input byte sequence digest_size (int) – the requested digest size; must be at most `BLAKE2B_BYTES_MAX`; the default digest size is `BLAKE2B_BYTES` key (bytes) – the key to be set for keyed MAC/PRF usage; if set, the key must be at most `BLAKE2B_KEYBYTES_MAX` long salt (bytes) – an initialization salt at most `BLAKE2B_SALTBYTES` long; it will be zero-padded if needed person (bytes) – a personalization string at most `BLAKE2B_PERSONALBYTES` long; it will be zero-padded if needed encoder (class) – the encoder to use on returned digest
Returns:	encoded bytes data
Return type:	the return type of the choosen encoder

nacl.hash.siphash24(message, key=b'', encoder=nacl.encoding.HexEncoder)[source]¶

Computes a keyed MAC of message using siphash-2-4

Parameters:	message (bytes) – The message to hash. key (bytes(`SIPHASH_KEYBYTES`)) – the message authentication key to be used It must be a `SIPHASH_KEYBYTES` long bytes sequence encoder – A class that is able to encode the hashed message.
Returns:	The hashed message.
Return type:	bytes(`SIPHASH_BYTES`) long bytes sequence

nacl.hash.siphashx24(message, key=b'', encoder=nacl.encoding.HexEncoder)[source]¶

New in version 1.2.

Computes a keyed MAC of message using the extended output length variant of siphash-2-4

Parameters:	message (bytes) – The message to hash. key (bytes(`SIPHASHX_KEYBYTES`)) – the message authentication key to be used It must be a `SIPHASHX_KEYBYTES` long bytes sequence encoder – A class that is able to encode the hashed message.
Returns:	The hashed message.
Return type:	bytes(`SIPHASHX_BYTES`) long bytes sequence

nacl.pwhash¶

The package pwhash provides implementations of modern memory-hard password hashing construction exposing modules with a uniform API.

Functions exposed at top level¶

The top level module only provides the functions implementing ascii encoded hashing and verification.

nacl.pwhash.str(password, opslimit=OPSLIMIT_INTERACTIVE, memlimit=MEMLIMIT_INTERACTIVE)[source]¶

Returns a password verifier hash, generated with the password hasher choosen as a default by libsodium.

Parameters:	password (bytes) – password used to seed the key derivation procedure; it length must be between `PASSWD_MIN` and `PASSWD_MAX` opslimit (int) – the time component (operation count) of the key derivation procedure’s computational cost; it must be between `OPSLIMIT_MIN` and `OPSLIMIT_MAX` memlimit (int) – the memory occupation component of the key derivation procedure’s computational cost; it must be between `MEMLIMIT_MIN` and `MEMLIMIT_MAX`
Returns:	the ascii encoded password hash along with a prefix encoding the used hashing construct, the random generated salt and the operation and memory limits used to generate the password hash
Return type:	bytes

As of PyNaCl version 1.2 this is nacl.pwhash.argon2id.str().

New in version 1.2.

nacl.pwhash.verify(password_hash, password)[source]¶: This function checks if hashing the proposed password, with the same construction and parameters encoded in the password hash would generate the same encoded string, thus verifying the correct password has been proposed in an authentication attempt.

New in version 1.2.

Module level constants

The top level module defines the constants related to the str() hashing construct and its corresponding verify() password verifier.

nacl.pwhash.PASSWD_MIN¶

nacl.pwhash.PASSWD_MAX¶: minimum and maximum length of the password to hash

nacl.pwhash.PWHASH_SIZE¶: maximum size of the encoded hash

nacl.pwhash.OPSLIMIT_MIN¶

nacl.pwhash.OPSLIMIT_MAX¶: minimum and maximum operation count for the hashing construct

nacl.pwhash.MEMLIMIT_MIN¶

nacl.pwhash.MEMLIMIT_MAX¶: minimum and maximum memory occupation for the hashing construct

and the recommended values for the opslimit and memlimit parameters

nacl.pwhash.MEMLIMIT_INTERACTIVE¶

nacl.pwhash.OPSLIMIT_INTERACTIVE¶: recommended values for the interactive user authentication password check case, leading to a sub-second hashing time

nacl.pwhash.MEMLIMIT_SENSITIVE¶

nacl.pwhash.OPSLIMIT_SENSITIVE¶: recommended values for generating a password hash/derived key meant to protect sensitive data, leading to a multi-second hashing time

nacl.pwhash.MEMLIMIT_MODERATE¶

nacl.pwhash.OPSLIMIT_MODERATE¶: values leading to a hashing time and memory cost intermediate between the interactive and the sensitive cases

Per-mechanism password hashing implementation modules¶

Along with the respective str() and verify() functions, the modules implementing named password hashing constructs expose also a kdf() function returning a raw pseudo-random bytes sequence derived from the input parameters

nacl.pwhash.argon2id¶

nacl.pwhash.argon2id.kdf(size, password, salt, opslimit=OPSLIMIT_SENSITIVE, memlimit=MEMLIMIT_SENSITIVE, encoder=nacl.encoding.RawEncoder)[source]¶

Derive a size bytes long key from a caller-supplied password and salt pair using the argon2id partially data dependent memory-hard construct.

Parameters:

size (int) – derived key size, must be between BYTES_MIN and BYTES_MAX
password (bytes) – password used to seed the key derivation procedure; it length must be between PASSWD_MIN and PASSWD_MAX
salt (bytes) – RANDOM salt used in the key derivation procedure; its length must be exactly SALTBYTES
opslimit (int) – the time component (operation count) of the key derivation procedure’s computational cost; it must be between OPSLIMIT_MIN and OPSLIMIT_MAX
memlimit (int) – the memory occupation component of the key derivation procedure’s computational cost; it must be between MEMLIMIT_MIN and MEMLIMIT_MAX

Return type:

bytes

The default settings for opslimit and memlimit are those deemed correct for generating a key, which can be used to protect sensitive data for a long time, leading to a multi-second hashing time.

New in version 1.2.

nacl.pwhash.argon2id.str(password, opslimit=OPSLIMIT_INTERACTIVE, memlimit=MEMLIMIT_INTERACTIVE)[source]¶

Returns a password verifier hash, generated with the argon2id password hasher.

See: nacl.pwhash.str() for the general API.

New in version 1.2.

nacl.pwhash.argon2id.verify(password_hash, password)[source]¶

This function verifies the proposed password, using password_hash as a password verifier.

See: nacl.pwhash.verify() for the general API.

New in version 1.2.

Module level constants

The module defines the constants related to the kdf() raw hashing construct

nacl.pwhash.argon2id.SALTBYTES¶: the length of the random bytes sequence passed in as a salt to the kdf()

nacl.pwhash.argon2id.BYTES_MIN¶

nacl.pwhash.argon2id.BYTES_MAX¶: the minimum and maximum allowed values for the size parameter of the kdf()

The meaning of each of the constants

nacl.pwhash.argon2id.PASSWD_MIN¶

nacl.pwhash.argon2id.PASSWD_MAX¶

nacl.pwhash.argon2id.PWHASH_SIZE¶

nacl.pwhash.argon2id.OPSLIMIT_MIN¶

nacl.pwhash.argon2id.OPSLIMIT_MAX¶

nacl.pwhash.argon2id.MEMLIMIT_MIN¶

nacl.pwhash.argon2id.MEMLIMIT_MAX¶

nacl.pwhash.argon2id.MEMLIMIT_INTERACTIVE¶

nacl.pwhash.argon2id.OPSLIMIT_INTERACTIVE¶

nacl.pwhash.argon2id.MEMLIMIT_SENSITIVE¶

nacl.pwhash.argon2id.OPSLIMIT_SENSITIVE¶

nacl.pwhash.argon2id.MEMLIMIT_MODERATE¶

nacl.pwhash.argon2id.OPSLIMIT_MODERATE¶: is the same as in nacl.hash.

nacl.pwhash.argon2i¶

nacl.pwhash.argon2i.kdf(size, password, salt, opslimit=OPSLIMIT_SENSITIVE, memlimit=MEMLIMIT_SENSITIVE, encoder=nacl.encoding.RawEncoder)[source]¶

Derive a size bytes long key from a caller-supplied password and salt pair using the argon2i data independent memory-hard construct.

See: py:func:nacl.pwhash.argon2id.kdf for the general API.

New in version 1.2.

nacl.pwhash.argon2i.str(password, opslimit=OPSLIMIT_INTERACTIVE, memlimit=MEMLIMIT_INTERACTIVE)[source]¶

Returns a password verifier hash, generated with the argon2i password hasher.

See: nacl.pwhash.str() for the general API.

New in version 1.2.

nacl.pwhash.argon2i.verify(password_hash, password)[source]¶

This function verifies the proposed password, using password_hash as a password verifier.

See: nacl.pwhash.verify() for the general API.

New in version 1.2.

Module level constants

The meaning of each of the constants

nacl.pwhash.argon2i.PASSWD_MIN¶

nacl.pwhash.argon2i.PASSWD_MAX¶

nacl.pwhash.argon2i.PWHASH_SIZE¶

nacl.pwhash.argon2i.SALTBYTES¶

nacl.pwhash.argon2i.BYTES_MIN¶

nacl.pwhash.argon2i.BYTES_MAX¶

nacl.pwhash.argon2i.OPSLIMIT_MIN¶

nacl.pwhash.argon2i.OPSLIMIT_MAX¶

nacl.pwhash.argon2i.MEMLIMIT_MIN¶

nacl.pwhash.argon2i.MEMLIMIT_MAX¶

nacl.pwhash.argon2i.MEMLIMIT_INTERACTIVE¶

nacl.pwhash.argon2i.OPSLIMIT_INTERACTIVE¶

nacl.pwhash.argon2i.MEMLIMIT_SENSITIVE¶

nacl.pwhash.argon2i.OPSLIMIT_SENSITIVE¶

nacl.pwhash.argon2i.MEMLIMIT_MODERATE¶

nacl.pwhash.argon2i.OPSLIMIT_MODERATE¶: is the same as in nacl.pwhash and nacl.pwhash.argon2id

nacl.pwhash.scrypt¶

nacl.pwhash.scrypt.kdf(size, password, salt, opslimit=OPSLIMIT_SENSITIVE, memlimit=MEMLIMIT_SENSITIVE, encoder=nacl.encoding.RawEncoder)[source]¶

Derive a size bytes long key from a caller-supplied password and salt pair using the scrypt data dependent memory-hard construct.

See: nacl.pwhash.argon2id.kdf() for the general API.

New in version 1.2.

nacl.pwhash.scrypt.str(password, opslimit=OPSLIMIT_INTERACTIVE, memlimit=MEMLIMIT_INTERACTIVE)[source]¶

Returns a password verifier hash, generated with the scrypt password hasher.

See: nacl.pwhash.str() for the general API.

New in version 1.2.

nacl.pwhash.scrypt.verify(password_hash, password)[source]¶

This function verifies the proposed password, using password_hash as a password verifier.

See: py:func:nacl.pwhash.verify for the general API.

New in version 1.2.

Module level constants

The meaning of each of the constants

nacl.pwhash.scrypt.PASSWD_MIN¶

nacl.pwhash.scrypt.PASSWD_MAX¶

nacl.pwhash.scrypt.PWHASH_SIZE¶

nacl.pwhash.scrypt.SALTBYTES¶

nacl.pwhash.scrypt.BYTES_MIN¶

nacl.pwhash.scrypt.BYTES_MAX¶

nacl.pwhash.scrypt.OPSLIMIT_MIN¶

nacl.pwhash.scrypt.OPSLIMIT_MAX¶

nacl.pwhash.scrypt.MEMLIMIT_MIN¶

nacl.pwhash.scrypt.MEMLIMIT_MAX¶

nacl.pwhash.scrypt.MEMLIMIT_INTERACTIVE¶

nacl.pwhash.scrypt.OPSLIMIT_INTERACTIVE¶

nacl.pwhash.scrypt.MEMLIMIT_SENSITIVE¶

nacl.pwhash.scrypt.OPSLIMIT_SENSITIVE¶

nacl.pwhash.scrypt.MEMLIMIT_MODERATE¶

nacl.pwhash.scrypt.OPSLIMIT_MODERATE¶: is the same as in nacl.pwhash and nacl.pwhash.argon2id

nacl.hashlib¶

The nacl.hashlib module exposes directly usable implementations of raw constructs which libsodium exposes with simplified APIs, like the ones in nacl.hash and in nacl.pwhash.

The blake2b and scrypt() implementations are as API compatible as possible with the corresponding ones added to cpython standard library’s hashlib module in cpython’s version 3.6.

class nacl.hashlib.blake2b(data=b'', digest_size=BYTES, key=b'', salt=b'', person=b'')[source]¶

Returns an hash object which exposes an API mostly compatible to python3.6’s hashlib.blake2b (the only difference being missing support for tree hashing parameters in the contructor)

The methods update(), copy(), digest() and hexdigest() have the same semantics as described in hashlib documentation.

Each instance exposes the digest_size, block_size name properties as required by hashlib API.

MAX_DIGEST_SIZE¶: the maximum allowed value of the requested digest_size

MAX_KEY_SIZE¶: the maximum allowed size of the password parameter

PERSON_SIZE¶: the maximimum size of the personalization

SALT_SIZE¶: the maximimum size of the salt

nacl.hashlib.scrypt(password, salt='', n=2**20, r=8, p=1, maxmem=2**25, dklen=64)[source]¶

Derive a raw cryptographic key using the scrypt KDF.

Parameters:

password (bytes) – the input password
salt (bytes) – a crypographically-strong random salt
n (int) – CPU/Memory cost factor
r (int) – block size multiplier: the used block size will be 128 * r
p (int) – requested parallelism: the number of indipendently running scrypt constructs which will contribute to the final key generation
maxmem (int) – maximum memory the whole scrypt construct will be entitled to use
dklen (int) – length of the derived key

Returns:

a buffer dklen bytes long containing the derived key

Implements the same signature as the hashlib.scrypt implemented in cpython version 3.6

The recommended values for n, r, p in 2012 were n = 2**14, r = 8, p = 1; as of 2016, libsodium suggests using n = 2**14, r = 8, p = 1 in a “interactive” setting and n = 2**20, r = 8, p = 1 in a “sensitive” setting.

The total memory usage will respectively be a little greater than 16MB in the “interactive” setting, and a little greater than 1GB in the “sensitive” setting.

Installation¶

Binary wheel install¶

PyNaCl ships as a binary wheel on OS X, Windows and Linux manylinux1 [1] , so all dependencies are included. Make sure you have an up-to-date pip and run:

$ pip install pynacl

Linux source build¶

PyNaCl relies on libsodium, a portable C library. A copy is bundled with PyNaCl so to install you can run:

$ pip install pynacl

If you’d prefer to use the version of libsodium provided by your distribution, you can disable the bundled copy during install by running:

$ SODIUM_INSTALL=system pip install pynacl

Warning

Usage of the legacy easy_install command provided by setuptools is generally discouraged, and is completely unsupported in PyNaCl’s case.

[1]	manylinux1 wheels are built on a baseline linux environment based on Centos 5.11 and should work on most x86 and x86_64 glibc based linux environments.

Doing A Release¶

To run a PyNaCl release follow these steps:

Update the version number in src/nacl/__init__.py.
Update README.rst changelog section with the date of the release.
Send a pull request with these items and wait for it to be merged.
Run invoke release {version}

Once the release script completes you can verify that the sdist and wheels are present on PyPI and then send a new PR to bump the version to the next major version (e.g. 1.2.0.dev1).

Reference vectors¶

In addition to the policy of keeping any code path in PyNaCl covered by unit tests, the output from cryptographic primitives and constructions must be verified as being conformant to the reference implementations or standards.

Imported reference vectors¶

Wherever possible it is the PyNaCl project’s policy to use existing reference vectors for primitives or constructions. These vectors should ideally be in their original format, but it is acceptable to make minimal changes to ease parsing at our discretion.

Box construction¶

The reference vector for testing the nacl.public.Box implementation come from libsodium’s test/default/box.c and test/default/box2.c and the corresponding expected outputs in test/default/box.exp and test/default/box2.exp

SecretBox construction¶

The reference vector for testing the nacl.secret.SecretBox implementation come from libsodium’s test/default/secretbox.c and the corresponding expected outputs in test/default/secretbox.exp

Custom generated reference vectors¶

In cases where there are no standardized test vectors, or the available ones are not applicable to libsodium’s implementation, test vectors are custom generated.

Argon2 constructs reference vectors¶

Since libsodium implements a different API for argon2 contructs than the one exposed by the reference implementation available at The password hash Argon2... <https://github.com/P-H-C/phc-winner-argon2/>, the kats data provided along to the reference implementation sources cannot be directly used as test vectors in PyNaCl tests.

Therefore, we are using a python driver for the command line argon2, which can be built following the instruction in the reference implementation sources.

Vector generation¶

The argondriver.py requires setting, via the command line option -x, the path to the argon2 executable; and as a default generates hex-encoded raw hash data on standard output.

Setting the -e option on the command line allows generating modular crypt formatted hashes.

The other command line options influence the minimum and maximum sizes of generated parameters as shown in the driver’s command line help, which is printed by inserting the -h option in the command line.

To generate vector data files in tests/data, the argondriver.py have been called to generate password hashes with parameters compatible with libsodium‘s implementation; in particular, the minimum operations count must be 3 for argon2i and 1 for argon2id, and the salt length must be 16 for raw hashes, and can vary for modular crypt formatted hashes.

The full command lines used in generating the vactors are:

for raw argon2i

python3 docs/vectors/python/argondriver.py \
             -x ~/phc-winner-argon2/argon2 \
             -c argon2i \
             -s 16 -S 16 -p 8 -P 16 -m 14 -M 18 \
             -l 18 -L 32 -t 3 -T 5 -n 10 \
             -w  tests/data/raw_argon2id_hashes.json

for raw argon2id

python3 docs/vectors/python/argondriver.py \
             -x ~/phc-winner-argon2/argon2 \
             -c argon2id \
             -s 16 -S 16 -p 8 -P 16 -m 14 -M 18 \
             -l 18 -L 32 -t 1 -T 5 -n 10 \
             -w  tests/data/raw_argon2id_hashes.json

for modular crypt argon2i

python3 docs/vectors/python/argondriver.py \
             -x ~/phc-winner-argon2/argon2 \
             -c argon2i -e \
             -s 8 -S 16 -p 8 -P 16 -m 14 -M 18 \
             -l 18 -L 32 -t 3 -T 5  -n 10 \
             -w  tests/data/modular_crypt_argon2id_hashes.json

for modular crypt argon2id

python3 docs/vectors/python/argondriver.py \
             -x ~/phc-winner-argon2/argon2 \
             -c argon2id -e \
             -s 8 -S 16 -p 8 -P 16 -m 14 -M 18 \
             -l 18 -L 32 -t 1 -T 5  -n 10 \
             -w  tests/data/modular_crypt_argon2id_hashes.json

Code for the vector generator driver¶

The code for argondriver.py is available inside the docs/vectors/python directory of PyNaCl distribution and can also be directly downloaded from argondriver.py.

argondriver.py¶

#!/usr/bin/python
#
from __future__ import division, print_function

import argparse
import json
import random
import string
import subprocess
import sys


class argonRunner(object):
    GOODCHARS = string.ascii_letters + string.digits

    def __init__(self, args):
        self.exe = args.exe
        self.mnsaltlen = args.mnsaltlen
        self.mnpwlen = args.mnpwlen
        self.mndgstlen = args.mndgstlen
        self.mnmem = args.mnmem
        self.mniters = args.mniters
        self.mxsaltlen = args.mxsaltlen
        self.mxpwlen = args.mxpwlen
        self.mxdgstlen = args.mxdgstlen
        self.mxmem = args.mxmem
        self.mxiters = args.mxiters
        self.encoded = args.encoded
        self.rng = random.SystemRandom()
        self.version = args.version
        self.construct = args.construct
        self.maxcount = args.n
        self.count = 0

    def _runOnce(self, passwd, salt, dgst_len, maxmem, iters):
        """
        """
        argv = [self.exe, salt.encode('ascii'),
                '-t', '{0:2d}'.format(iters),
                '-m', '{0:2d}'.format(maxmem),
                '-l', '{0:3d}'.format(dgst_len),
                '-v', self.version,
                ]

        if self.encoded:
            argv.append('-e')
            mode = 'crypt'
        else:
            argv.append('-r')
            mode = 'raw'
        if self.construct == 'argon2i':
            argv.append('-i')
        elif self.construct == 'argon2d':
            argv.append('-d')
        elif self.construct == 'argon2id':
            argv.append('-id')
        p = subprocess.Popen(argv, stdin=subprocess.PIPE,
                             stdout=subprocess.PIPE)
        out, err = p.communicate(passwd.encode('ascii'))
        return dict(passwd=passwd, salt=salt, dgst_len=dgst_len,
                    maxmem=2 ** maxmem, iters=iters, mode=mode,
                    pwhash=out.decode('ascii').rstrip(),
                    construct=self.construct,
                    )

    def _genSalt(self):
        sltln = self.rng.randint(self.mnsaltlen, self.mxsaltlen)
        chrs = [self.rng.choice(self.GOODCHARS) for x in range(sltln)]
        return ''.join(chrs)

    def _genPw(self):
        pwln = self.rng.randint(self.mnpwlen, self.mxpwlen)
        chrs = [self.rng.choice(self.GOODCHARS) for x in range(pwln)]
        return ''.join(chrs)

    def __next__(self):
        if self.count >= self.maxcount:
            raise StopIteration
        psw = self._genPw()
        slt = self._genSalt()
        mem = self.rng.randint(self.mnmem, self.mxmem)
        iters = self.rng.randint(self.mniters, self.mxiters)
        dgstln = self.rng.randint(self.mndgstlen, self.mxdgstlen)
        rs = self._runOnce(psw, slt, dgstln, mem, iters)
        self.count += 1
        return rs

    def __iter__(self):
        return self

    next = __next__


if __name__ == '__main__':

    p = argparse.ArgumentParser()
    p.add_argument('-x', '--executable', dest='exe', required=True)
    p.add_argument('-c', '--construction', dest='construct',
                   type=str, default='argon2i')
    p.add_argument('-v', '--version', dest='version',
                   type=str, default='13')
    p.add_argument('-e', '--encoded', dest='encoded', default=False,
                   action='store_true',)
    p.add_argument('-s', '--min-salt-len', dest='mnsaltlen', type=int,
                   default=8)
    p.add_argument('-S', '--max-salt-len', dest='mxsaltlen', type=int,
                   default=8)
    p.add_argument('-p', '--min-password-len', dest='mnpwlen',
                   type=int, default=16)
    p.add_argument('-P', '--max-password-len', dest='mxpwlen',
                   type=int, default=16)
    p.add_argument('-l', '--min-digest-len', dest='mndgstlen',
                   type=int, default=64)
    p.add_argument('-L', '--max-digest-len', dest='mxdgstlen',
                   type=int, default=64)
    p.add_argument('-m', '--min-memory-exponent', dest='mnmem',
                   type=int, default=16)
    p.add_argument('-M', '--max-memory-exponent', dest='mxmem',
                   type=int, default=16)
    p.add_argument('-t', '--min-time-opscount', dest='mniters',
                   type=int, default=3)
    p.add_argument('-T', '--max-time-opscount', dest='mxiters',
                   type=int, default=3)
    p.add_argument('-n', '--count', dest='n', type=int, default=10)
    p.add_argument('-w', '--output', dest='outfile',
                   default=sys.stdout, type=argparse.FileType('w'))

    args = p.parse_args()

    res = [x for x in argonRunner(args)]

    json.dump(res, args.outfile, indent=2, separators=(',', ': '))

SealedBox reference vectors¶

Since libsodium’s tests do not provide reference data for the SealedBox construction, the implementation is verified with a sealbox_test_vectors utility program that produces and checks custom test vectors by making specific calls to libsodium API.

To build the sealbox_test_vectors you need a C language compiler, a prebuilt libsodium library more recent than version 1.0.3 and the corresponding include headers.

In a UNIX-like programming environment you should then execute:

$ cc -o sealbox_test_vectors sealbox_test_vectors.c -lsodium -lc

If you prefer using a locally compiled installation of the bundled sources, refer to Building the bundled library and then run:

$ cc -o sealbox_test_vectors sealbox_test_vectors.c \
  ${SODIUMINCL} ${SODIUMLIB} -lsodium -lc

Vector generation¶

When called with one or more command line arguments, sealbox_test_vectors will generate the number of hex-encoded vectors requested as first argument, with the optional second and third arguments influencing the length of the randomly generated messages:

$ ./sealbox_test_vectors 1
XXXX...        XXXX...        <len>:XXXX...        <len>:XXXX...

The second argument, if present, sets both a minimum and a maximum length on generated messages, overriding the default 128 bytes values respectively with the supplied value and with twice the supplied value.

The third argument, if present, sets the maximum length of generated messages.

Vector test¶

When called without command line arguments, sealbox_test_vectors will parse and hex-decode the lines given as standard input and check if decoding the encrypted message will return the original message. A “OK”/”FAIL” tag will be appended to the input line to signify success/failure of the test.

To check correct “round-trip” behavior, you can run sealbox_test_vectors as a test vector generator against itself:

$ ./sealbox_test_vectors 1 | ./sealbox_test_vectors
XXXX...     XXXX... <len>:XXXX...   <len>:XXXX...   OK

If you want to check the vectors distributed with PyNaCl’s sources, after setting the environment variable PYNACL_BASE to the directory where the unpacked source for PyNaCl has been extracted/cloned, you could run:

$ ./sealbox_test_vectors < ${PYNACL_BASE}/tests/data/sealed_box_ref.txt
77076d ... 8c86  OK

Source code for the vector checker utility¶

The source code for sealbox_test_vectors is available inside the docs/vectors/c-source directory of PyNaCl distribution and can also be directly downloaded from sealbox_test_vectors.c.

sealbox_test_vectors.c¶

/*
 * Copyright 2017 Donald Stufft and individual contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Test vector generator/checker for libsodium's box_seal APIs
 * to build in a unix-like environment, use a command line like
 * $ cc sealbox_test_vectors.c -I${IPATH} -L${LPATH} -lsodium -o sealbox_test_vectors
 * with IPATH and LPATH defined to respectively point to libsodium's include path
 * and to the directory containing the link library libsodium.a or libsodium.o
 *
 */
#include <stdio.h>
#include <string.h>
#include <sodium.h>

int checkone (char *hxsecret, char *hxpub, size_t ptlen, char *hxplaintext,
	      size_t crlen, char *hxencrypted) {

    int pklen = crypto_box_PUBLICKEYBYTES;
    int sklen = crypto_box_SECRETKEYBYTES;

    char *skr = sodium_malloc (sklen);
    char *pub = sodium_malloc (pklen);
    char *txt = sodium_malloc (ptlen);
    char *crpt = sodium_malloc (crlen);
    char *outp = sodium_malloc (ptlen);

    int rs = sodium_hex2bin (skr, sklen, hxsecret, 2 * sklen,
                             NULL, NULL, NULL);
    rs |= sodium_hex2bin (pub, pklen, hxpub, 2 * pklen, NULL, NULL, NULL);
    rs |= sodium_hex2bin (txt, ptlen, hxplaintext, strlen (hxplaintext),
                          NULL, NULL, NULL);
    rs |= sodium_hex2bin (crpt, crlen, hxencrypted, strlen (hxencrypted),
                          NULL, NULL, NULL);

    if (rs == 0)
        rs = crypto_box_seal_open (outp, crpt, crlen, pub, skr);
    if (rs == 0)
        rs = sodium_memcmp (outp, txt, ptlen);

    sodium_free (crpt);
    sodium_free (txt);
    sodium_free (skr);
    sodium_free (pub);

    return rs;
}

void gentestline (int minmsglen, int maxmsglen) {

    int pklen = crypto_box_PUBLICKEYBYTES;
    int sklen = crypto_box_SECRETKEYBYTES;
    size_t txtlen = minmsglen + randombytes_uniform (maxmsglen - minmsglen + 1);
    size_t encrlen = txtlen + crypto_box_SEALBYTES;

    char *skr = sodium_malloc (sklen);
    char *pub = sodium_malloc (pklen);
    char *txt = sodium_malloc (txtlen);
    char *crpt = sodium_malloc (encrlen);

    crypto_box_keypair (pub, skr);
    randombytes_buf (txt, txtlen);

    crypto_box_seal (crpt, txt, txtlen, pub);

    char *hskr = sodium_malloc (sklen * 2 + 1);
    char *hpub = sodium_malloc (pklen * 2 + 1);
    char *htxt = sodium_malloc (txtlen * 2 + 1);
    char *hkrp = sodium_malloc (encrlen * 2 + 1);

    sodium_bin2hex (hskr, sklen * 2 + 1, skr, sklen);
    sodium_bin2hex (hpub, pklen * 2 + 1, pub, pklen);
    sodium_bin2hex (htxt, txtlen * 2 + 1, txt, txtlen);
    sodium_bin2hex (hkrp, encrlen * 2 + 1, crpt, encrlen);

    printf ("%s\t%s\t%zu:%s\t%zu:%s\n", hskr, hpub, txtlen, htxt, encrlen, hkrp);
}

int main (int argc, char **argv) {
/*
 * If called without any argument, the resulting executable will
 * read and hex decode the secret and public part of the receiver key,
 * the original plaintext and the ciphertext, and then
 * check if the message resulting from decrypting ciphertext with
 * the secret key is equal to the given plaintext
 *
 * If called with a sequence of integer arguments, sealbox_test_vectors
 * will generate the requested number of reference lines, encrypting 
 * random messages.
 *
 */
    if (sodium_init () == -1) {
        exit (1);
    }

    if (argc == 1) {
        size_t lsz = 0;
        char *line = NULL;
        ssize_t lln = 0;
        int res;
        char hxsecret[2 * crypto_box_SECRETKEYBYTES + 1];
        char hxpub[2 * crypto_box_PUBLICKEYBYTES + 1];
        char hxplaintext[2048 + 1];
        char hxencrypted[2048 + 2 * crypto_box_SEALBYTES + 1];
        char cmpplaintext[5 + 2048 + 1];
        char cmpencrypted[5 + 2048 + 2 * crypto_box_SEALBYTES + 1];
        size_t ptlen = 0;
        size_t crlen = 0;

        while (lln = getline (&line, &lsz, stdin) > 0) {
            if (lln > 0) {
                if (strncmp (line, "#", 1) == 0 ||
                        strncmp (line, "\n", 1) == 0 ||
                        strncmp (line, "\r", 1) == 0)
                    continue;

                sscanf (line, "%s%s%s%s",
                        hxsecret, hxpub, cmpplaintext, cmpencrypted);
                sscanf (cmpplaintext, "%zu:%s",
                        &ptlen, hxplaintext);
                sscanf (cmpencrypted, "%zu:%s",
                        &crlen, hxencrypted);
                if (ptlen == 0)
                        memset(hxplaintext, 0, sizeof(hxplaintext));
                if (crlen == 0)
                        memset(hxencrypted, 0, sizeof(hxencrypted));
                res = checkone (hxsecret, hxpub, ptlen, hxplaintext, crlen, hxencrypted);
                char *rsstr = (res == 0) ? "OK" : "FAIL";
                printf ("%s\t%s\t%zu:%s\t%zu:%s\t%s\n",
                        hxsecret, hxpub, ptlen, hxplaintext, crlen, hxencrypted, rsstr);
            }
            free (line);
            line = NULL;
        }
    } else {
        int nlines = atoi (argv[1]);
        int minmsgl = 128;
        int maxmsgl = 128;
        if (argc == 3) {
            minmsgl = atoi (argv[2]);
            maxmsgl = atoi (argv[2]) * 2;
        } else if (argc == 4) {
            minmsgl = atoi (argv[2]);
            maxmsgl = atoi (argv[3]);
        }
        for (int i = 0; i < nlines; i++) {
            gentestline (minmsgl, maxmsgl);
        }
    }
}

Building the bundled library¶

If you you want to avoid a system-wide installation of libsodium’s development files just for compiling and running the tests, you can instead install the library and header files inside PyNaCl’s sources.

Linux systems¶

On Linux (and presumably other UNIX-like systems), after entering the PyNaCl source directory you must execute the following commands:

$ mkdir -p build/libsodium
$ cd build/libsodium
$ ../../src/libsodium/configure --prefix=$PWD --disable-shared
$ make
$ make install
$ cd ../..

If all went well,

$ ls build/libsodium/{lib,include}

should generate something like the following output:

build/libsodium/include:
sodium  sodium.h

build/libsodium/lib:
libsodium.a  libsodium.la  pkgconfig

If you now define and export the

$ SODIUMINCL="-I${PWD}/build/libsodium/include"
$ export SODIUMINCL
$ SODIUMLIB="-L${PWD}/build/libsodium/lib"
$ export SODIUMLIB

environment variables, you can instruct the compiler to use the just-installed library by simply dereferencing the path flags on the c compier command line

$ cc ${SODIUMINCL} ${SODIUMLIB}

Changelog¶

1.2.0 - 2017-11-01¶

Update libsodium to 1.0.15.
Infrastructure: add jenkins support for automatic build of manylinux1 binary wheels
Added support for SealedBox construction.
Added support for argon2i and argon2id password hashing constructs and restructured high-level password hashing implementation to expose the same interface for all hashers.
Added support for 128 bit siphashx24 variant of siphash24.
Added support for from_seed APIs for X25519 keypair generation.
Dropped support for Python 3.3.

1.1.2 - 2017-03-31¶

reorder link time library search path when using bundled libsodium

1.1.1 - 2017-03-15¶

Fixed a circular import bug in nacl.utils.

1.1.0 - 2017-03-14¶

Dropped support for Python 2.6.
Added shared_key() method on Box.
You can now pass None to nonce when encrypting with Box or SecretBox and it will automatically generate a random nonce.
Added support for siphash24.
Added support for blake2b.
Added support for scrypt.
Update libsodium to 1.0.11.
Default to the bundled libsodium when compiling.
All raised exceptions are defined mixing-in nacl.exceptions.CryptoError

1.0.1 - 2016-01-24¶

Fix an issue with absolute paths that prevented the creation of wheels.

1.0 - 2016-01-23¶

PyNaCl has been ported to use the new APIs available in cffi 1.0+. Due to this change we no longer support PyPy releases older than 2.6.
Python 3.2 support has been dropped.
Functions to convert between Ed25519 and Curve25519 keys have been added.

0.3.0 - 2015-03-04¶

The low-level API (nacl.c.*) has been changed to match the upstream NaCl C/C++ conventions (as well as those of other NaCl bindings). The order of arguments and return values has changed significantly. To avoid silent failures, nacl.c has been removed, and replaced with nacl.bindings (with the new argument ordering). If you have code which calls these functions (e.g. nacl.c.crypto_box_keypair()), you must review the new docstrings and update your code/imports to match the new conventions.

PyNaCl: Python binding to the libsodium library¶

Features¶

Contents¶

Public Key Encryption¶

Examples¶

nacl.public.Box¶

nacl.public.SealedBox¶

Reference¶

Algorithm¶

Secret Key Encryption¶

Example¶

Requirements¶

Key¶

Nonce¶

Reference¶

Algorithm details¶

Digital Signatures¶

Example¶

Reference¶

Ed25519¶

Algorithm¶

Hashing¶

Integrity check examples¶

Additional hashing usages for blake2b¶

Message authentication¶

Message authentication example¶

Key derivation¶

Key derivation example¶

Password hashing¶

Hashers and parameters¶

Password storage and verification¶

Key derivation¶

Module level constants for operation and memory cost tweaking¶

Support Features¶

Encoders¶

Built in Encoders¶

Defining your own Encoder¶

Exceptions¶

PyNaCl specific exceptions¶

PyNaCl exceptions mixing-in standard library ones¶

Utilities¶

nacl.hash¶

nacl.pwhash¶

Functions exposed at top level¶

Per-mechanism password hashing implementation modules¶

nacl.pwhash.argon2id¶

nacl.pwhash.argon2i¶

nacl.pwhash.scrypt¶

nacl.hashlib¶

Installation¶

Binary wheel install¶

Linux source build¶

Doing A Release¶

Reference vectors¶

Imported reference vectors¶

Box construction¶

SecretBox construction¶

Custom generated reference vectors¶

Argon2 constructs reference vectors¶

Vector generation¶

Code for the vector generator driver¶

SealedBox reference vectors¶

Vector generation¶

Vector test¶

Source code for the vector checker utility¶

Building the bundled library¶

Linux systems¶

Changelog¶

1.2.0 - 2017-11-01¶

1.1.2 - 2017-03-31¶

1.1.1 - 2017-03-15¶

1.1.0 - 2017-03-14¶

1.0.1 - 2016-01-24¶

1.0 - 2016-01-23¶

0.3.0 - 2015-03-04¶

Indices and tables¶

Additional hashing usages for `blake2b`¶