Danger

This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.

Message digests (Hashing)

class cryptography.hazmat.primitives.hashes.Hash(algorithm)

A cryptographic hash function takes an arbitrary block of data and calculates a fixed-size bit string (a digest), such that different data results (with a high probability) in different digests.

This is an implementation of HashContext meant to be used with HashAlgorithm implementations to provide an incremental interface to calculating various message digests.

>>> from cryptography.hazmat.primitives import hashes
>>> digest = hashes.Hash(hashes.SHA256())
>>> digest.update(b"abc")
>>> digest.update(b"123")
>>> digest.finalize()
b'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90'

Keep in mind that attacks against cryptographic hashes only get stronger with time, and that often algorithms that were once thought to be strong, become broken. Because of this it’s important to include a plan for upgrading the hash algorithm you use over time. For more information, see Lifetimes of cryptographic hash functions.

Parameters:

algorithm – A HashAlgorithm instance such as those described below.

Raises:

cryptography.exceptions.UnsupportedAlgorithm – This is raised if the provided algorithm is unsupported.

update(data)

Parameters:

data (bytes) – The bytes to be hashed.

Raises:

• cryptography.exceptions.AlreadyFinalized – See finalize().

• TypeError – This exception is raised if data is not bytes.

copy()

Copy this Hash instance, usually so that you may call finalize() to get an intermediate digest value while we continue to call update() on the original instance.

Returns:

A new instance of Hash that can be updated and finalized independently of the original instance.

Raises:

cryptography.exceptions.AlreadyFinalized – See finalize().

finalize()

Finalize the current context and return the message digest as bytes.

After finalize has been called this object can no longer be used and update(), copy(), and finalize() will raise an AlreadyFinalized exception.

Return bytes:

The message digest as bytes.

class cryptography.hazmat.primitives.hashes.XOFHash(algorithm)

An extendable output function (XOF) is a cryptographic hash function that can produce an arbitrary amount of output for a given input. The output can be obtained by repeatedly calling squeeze() with the desired length.

>>> import sys
>>> from cryptography.hazmat.primitives import hashes
>>> digest = hashes.XOFHash(hashes.SHAKE128(digest_size=sys.maxsize))
>>> digest.update(b"abc")
>>> digest.update(b"123")
>>> digest.squeeze(16)
b'\x18\xd6\xbd\xeb5u\x83[@\xfa%/\xdc\xca\x9f\x1b'
>>> digest.squeeze(16)
b'\xc2\xeb\x12\x05\xc3\xf9Bu\x88\xe0\xda\x80FvAV'

Parameters:

algorithm – A ExtendableOutputFunction instance such as those described below. The digest_size passed is the maximum number of bytes that can be squeezed from the XOF when using this class.

Raises:

cryptography.exceptions.UnsupportedAlgorithm – This is raised if the provided algorithm is unsupported.

update(data)

Parameters:

data (bytes) – The bytes to be hashed.

Raises:

• cryptography.exceptions.AlreadyFinalized – If already squeezed.

• TypeError – This exception is raised if data is not bytes.

copy()

Copy this XOFHash instance, usually so that you may call squeeze() to get an intermediate digest value while we continue to call update() on the original instance.

Returns:

A new instance of XOFHash that can be updated and squeezed independently of the original instance. If you copy an instance that has already been squeezed, the copy will also be in a squeezed state.

Raises:

cryptography.exceptions.AlreadyFinalized – See squeeze().

squeeze(length)

Parameters:

length (int) – The number of bytes to squeeze.

After squeeze() has been called this object can no longer be updated and update(), will raise an AlreadyFinalized exception.

Return bytes:

length bytes of output from the extendable output function (XOF).

Raises:

ValueError – If the maximum number of bytes that can be squeezed has been exceeded.

SHA-2 family

class cryptography.hazmat.primitives.hashes.SHA224

SHA-224 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 224-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA256

SHA-256 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 256-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA384

SHA-384 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 384-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA512

SHA-512 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 512-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA512_224

Added in version 2.5.

SHA-512/224 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 224-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA512_256

Added in version 2.5.

SHA-512/256 is a cryptographic hash function from the SHA-2 family and is standardized by NIST. It produces a 256-bit message digest.

BLAKE2

BLAKE2 is a cryptographic hash function specified in RFC 7693. BLAKE2’s design makes it immune to length-extension attacks, an advantage over the SHA-family of hashes.

Note

While the RFC specifies keying, personalization, and salting features, these are not supported at this time due to limitations in OpenSSL.

class cryptography.hazmat.primitives.hashes.BLAKE2b(digest_size)

BLAKE2b is optimized for 64-bit platforms and produces an 1 to 64-byte message digest.

Parameters:

digest_size (int) – The desired size of the hash output in bytes. Only 64 is supported at this time.

Raises:

ValueError – If the digest_size is invalid.

class cryptography.hazmat.primitives.hashes.BLAKE2s(digest_size)

BLAKE2s is optimized for 8 to 32-bit platforms and produces a 1 to 32-byte message digest.

Parameters:

digest_size (int) – The desired size of the hash output in bytes. Only 32 is supported at this time.

Raises:

ValueError – If the digest_size is invalid.

SHA-3 family

SHA-3 is the most recent NIST secure hash algorithm standard. Despite the larger number SHA-3 is not considered to be better than SHA-2. Instead, it uses a significantly different internal structure so that if an attack appears against SHA-2 it is unlikely to apply to SHA-3. SHA-3 is significantly slower than SHA-2 so at this time most users should choose SHA-2.

class cryptography.hazmat.primitives.hashes.SHA3_224

Added in version 2.5.

SHA3/224 is a cryptographic hash function from the SHA-3 family and is standardized by NIST. It produces a 224-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA3_256

Added in version 2.5.

SHA3/256 is a cryptographic hash function from the SHA-3 family and is standardized by NIST. It produces a 256-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA3_384

Added in version 2.5.

SHA3/384 is a cryptographic hash function from the SHA-3 family and is standardized by NIST. It produces a 384-bit message digest.

class cryptography.hazmat.primitives.hashes.SHA3_512

Added in version 2.5.

SHA3/512 is a cryptographic hash function from the SHA-3 family and is standardized by NIST. It produces a 512-bit message digest.

SHA-1

Warning

SHA-1 is a deprecated hash algorithm that has practical known collision attacks. You are strongly discouraged from using it. Existing applications should strongly consider moving away.

class cryptography.hazmat.primitives.hashes.SHA1

SHA-1 is a cryptographic hash function standardized by NIST. It produces an 160-bit message digest. Cryptanalysis of SHA-1 has demonstrated that it is vulnerable to practical collision attacks, and collisions have been demonstrated.

MD5

Warning

MD5 is a deprecated hash algorithm that has practical known collision attacks. You are strongly discouraged from using it. Existing applications should strongly consider moving away.

class cryptography.hazmat.primitives.hashes.MD5

MD5 is a deprecated cryptographic hash function. It produces a 128-bit message digest and has practical known collision attacks.

SM3

class cryptography.hazmat.primitives.hashes.SM3

Added in version 35.0.0.

SM3 is a cryptographic hash function standardized by the Chinese National Cryptography Administration in GM/T 0004-2012. It produces 256-bit message digests. (An English description is available at draft-sca-cfrg-sm3.) This hash should be used for compatibility purposes where required and is not otherwise recommended for use.

Extendable Output Functions

class cryptography.hazmat.primitives.hashes.SHAKE128(digest_size)

Added in version 2.5.

SHAKE128 is an extendable output function (XOF) based on the same core permutations as SHA3. It allows the caller to obtain an arbitrarily long digest length. Longer lengths, however, do not increase security or collision resistance and lengths shorter than 128 bit (16 bytes) will decrease it.

This class can be used with Hash or XOFHash. When used in Hash finalize() will return digest_size bytes. When used in XOFHash this defines the total number of bytes allowed to be squeezed.

Parameters:

digest_size (int) – The length of output desired. Must be greater than zero.

Raises:

ValueError – If the digest_size is invalid.

class cryptography.hazmat.primitives.hashes.SHAKE256(digest_size)

Added in version 2.5.

SHAKE256 is an extendable output function (XOF) based on the same core permutations as SHA3. It allows the caller to obtain an arbitrarily long digest length. Longer lengths, however, do not increase security or collision resistance and lengths shorter than 256 bit (32 bytes) will decrease it.

This class can be used with Hash or XOFHash. When used in Hash finalize() will return digest_size bytes. When used in XOFHash this defines the total number of bytes allowed to be squeezed.

Parameters:

digest_size (int) – The length of output desired. Must be greater than zero.

Raises:

ValueError – If the digest_size is invalid.

Interfaces

class cryptography.hazmat.primitives.hashes.HashAlgorithm

name

Type:

str

The standard name for the hash algorithm, for example: "sha256" or "blake2b".

digest_size

Type:

int

The size of the resulting digest in bytes.

class cryptography.hazmat.primitives.hashes.ExtendableOutputFunction

An interface applied to hashes that act as extendable output functions (XOFs). The currently supported XOFs are SHAKE128 and SHAKE256.

class cryptography.hazmat.primitives.hashes.HashContext

algorithm

A HashAlgorithm that will be used by this context.

update(data)

Parameters:

data (bytes) – The data you want to hash.

finalize()

Returns:

The final digest as bytes.

copy()

Returns:

A HashContext that is a copy of the current context.