bcrypt

Acceptable password hashing for your software and your servers (but you should really use argon2id or scrypt)

Installation

To install bcrypt, simply:

$ pip install bcrypt

Note that bcrypt should build very easily on Linux provided you have a C compiler and a Rust compiler (the minimum supported Rust version is 1.56.0).

For Debian and Ubuntu, the following command will ensure that the required dependencies are installed:

$ sudo apt-get install build-essential cargo

For Fedora and RHEL-derivatives, the following command will ensure that the required dependencies are installed:

$ sudo yum install gcc cargo

For Alpine, the following command will ensure that the required dependencies are installed:

$ apk add --update musl-dev gcc cargo

Alternatives

While bcrypt remains an acceptable choice for password storage, depending on your specific use case you may also want to consider using scrypt (either via standard library or cryptography) or argon2id via argon2_cffi.

Changelog

Unreleased

• Dropped support for Python 3.7.

4.2.1

• Bump Rust dependency versions - this should resolve crashes on Python 3.13 free-threaded builds.
• We no longer build manylinux wheels for PyPy 3.9.

4.2.0

• Bump Rust dependency versions
• Removed the BCRYPT_ALLOW_RUST_163 environment variable.

4.1.3

• Bump Rust dependency versions

4.1.2

• Publish both py37 and py39 wheels. This should resolve some errors relating to initializing a module multiple times per process.

4.1.1

• Fixed the type signature on the kdf method.
• Fixed packaging bug on Windows.
• Fixed incompatibility with passlib package detection assumptions.

4.1.0

• Dropped support for Python 3.6.
• Bumped MSRV to 1.64. (Note: Rust 1.63 can be used by setting the BCRYPT_ALLOW_RUST_163 environment variable)

4.0.1

• We now build PyPy manylinux wheels.
• Fixed a bug where passing an invalid salt to checkpw could result in a pyo3_runtime.PanicException. It now correctly raises a ValueError.

4.0.0

• bcrypt is now implemented in Rust. Users building from source will need to have a Rust compiler available. Nothing will change for users downloading wheels.
• We no longer ship manylinux2010 wheels. Users should upgrade to the latest pip to ensure this doesn’t cause issues downloading wheels on their platform. We now ship manylinux_2_28 wheels for users on new enough platforms.
• NUL bytes are now allowed in inputs.

3.2.2

• Fixed packaging of py.typed files in wheels so that mypy works.

3.2.1

• Added support for compilation on z/OS
• The next release of bcrypt with be 4.0 and it will require Rust at compile time, for users building from source. There will be no additional requirement for users who are installing from wheels. Users on most platforms will be able to obtain a wheel by making sure they have an up to date pip. The minimum supported Rust version will be 1.56.0.
• This will be the final release for which we ship manylinux2010 wheels. Going forward the minimum supported manylinux ABI for our wheels will be manylinux2014. The vast majority of users will continue to receive manylinux wheels provided they have an up to date pip.

3.2.0

• Added typehints for library functions.
• Dropped support for Python versions less than 3.6 (2.7, 3.4, 3.5).
• Shipped abi3 Windows wheels (requires pip >= 20).

3.1.7

• Set a setuptools lower bound for PEP517 wheel building.
• We no longer distribute 32-bit manylinux1 wheels. Continuing to produce them was a maintenance burden.

3.1.6

• Added support for compilation on Haiku.

3.1.5

• Added support for compilation on AIX.
• Dropped Python 2.6 and 3.3 support.
• Switched to using abi3 wheels for Python 3. If you are not getting a wheel on a compatible platform please upgrade your pip version.

3.1.4

• Fixed compilation with mingw and on illumos.

3.1.3

• Fixed a compilation issue on Solaris.
• Added a warning when using too few rounds with kdf.

3.1.2

• Fixed a compile issue affecting big endian platforms.
• Fixed invalid escape sequence warnings on Python 3.6.
• Fixed building in non-UTF8 environments on Python 2.

3.1.1

• Resolved a UserWarning when used with cffi 1.8.3.

3.1.0

• Added support for checkpw, a convenience method for verifying a password.
• Ensure that you get a $2y$ hash when you input a $2y$ salt.
• Fixed a regression where $2a hashes were vulnerable to a wraparound bug.
• Fixed compilation under Alpine Linux.

3.0.0

• Switched the C backend to code obtained from the OpenBSD project rather than openwall.
• Added support for bcrypt_pbkdf via the kdf function.

2.0.0

• Added support for an adjustible prefix when calling gensalt.
• Switched to CFFI 1.0+

Usage

Password Hashing

Hashing and then later checking that a password matches the previous hashed password is very simple:

>>> import bcrypt
>>> password = b"super secret password"
>>> # Hash a password for the first time, with a randomly-generated salt
>>> hashed = bcrypt.hashpw(password, bcrypt.gensalt())
>>> # Check that an unhashed password matches one that has previously been
>>> # hashed
>>> if bcrypt.checkpw(password, hashed):
...     print("It Matches!")
... else:
...     print("It Does not Match :(")

KDF

As of 3.0.0 bcrypt now offers a kdf function which does bcrypt_pbkdf. This KDF is used in OpenSSH's newer encrypted private key format.

>>> import bcrypt
>>> key = bcrypt.kdf(
...     password=b'password',
...     salt=b'salt',
...     desired_key_bytes=32,
...     rounds=100)

Adjustable Work Factor

One of bcrypt's features is an adjustable logarithmic work factor. To adjust the work factor merely pass the desired number of rounds to bcrypt.gensalt(rounds=12) which defaults to 12):

>>> import bcrypt
>>> password = b"super secret password"
>>> # Hash a password for the first time, with a certain number of rounds
>>> hashed = bcrypt.hashpw(password, bcrypt.gensalt(14))
>>> # Check that a unhashed password matches one that has previously been
>>> #   hashed
>>> if bcrypt.checkpw(password, hashed):
...     print("It Matches!")
... else:
...     print("It Does not Match :(")

Adjustable Prefix

Another one of bcrypt's features is an adjustable prefix to let you define what libraries you'll remain compatible with. To adjust this, pass either 2a or 2b (the default) to bcrypt.gensalt(prefix=b"2b") as a bytes object.

As of 3.0.0 the $2y$ prefix is still supported in hashpw but deprecated.

Maximum Password Length

The bcrypt algorithm only handles passwords up to 72 characters, any characters beyond that are ignored. To work around this, a common approach is to hash a password with a cryptographic hash (such as sha256) and then base64 encode it to prevent NULL byte problems before hashing the result with bcrypt:

>>> password = b"an incredibly long password" * 10
>>> hashed = bcrypt.hashpw(
...     base64.b64encode(hashlib.sha256(password).digest()),
...     bcrypt.gensalt()
... )

Compatibility

This library should be compatible with py-bcrypt and it will run on Python 3.6+, and PyPy 3.

Security

bcrypt follows the same security policy as cryptography, if you identify a vulnerability, we ask you to contact us privately.