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.
The OpenSSL C library. Cryptography supports OpenSSL version 1.0.2 and greater.
This is the exposed API for the OpenSSL backend.
It implements the following interfaces:
It also implements the following interface for OpenSSL versions
It also exposes the following:
The string name of this backend:
Return text: The friendly string name of the loaded OpenSSL library. This is not necessarily the same version as it was compiled against.
New in version 1.8.
Return int: The integer version of the loaded OpenSSL library. This is defined in
OPENSSL_VERSION_NUMBERand is typically shown in hexadecimal (e.g.
0x1010003f). This is not necessarily the same version as it was compiled against.
Activates the OS random engine. This will effectively disable OpenSSL’s default CSPRNG.
New in version 1.7.
Returns the implementation of OS random engine.
This will activate the default OpenSSL CSPRNG.
OS random engine¶
As of OpenSSL 1.1.1d its CSPRNG is fork-safe by default.
cryptography does not compile or load the custom engine on
By default OpenSSL uses a user-space CSPRNG that is seeded from system random (
CryptGenRandom). This CSPRNG is not reseeded
automatically when a process calls
fork(). This can result in situations
where two different processes can return similar or identical keys and
compromise the security of the system.
The approach this project has chosen to mitigate this vulnerability is to
include an engine that replaces the OpenSSL default CSPRNG with one that
sources its entropy from
/dev/urandom on UNIX-like operating systems and
CryptGenRandom on Windows. This method of pulling from the system pool
allows us to avoid potential issues with initializing the RNG as well as
protecting us from the
This engine is active by default when importing the OpenSSL backend. When active this engine will be used to generate all the random data OpenSSL requests.
When importing only the binding it is added to the engine list but not activated.
OS random sources¶
On Windows the implementation of
CryptGenRandom depends on which version of
the operation system you are using. See the Microsoft documentation for more
Linux uses its own PRNG design.
/dev/urandom is a non-blocking source
seeded from the same pool as
|Linux >= 3.17 with working
|OpenBSD >= 5.6||
|BSD family (including macOS 10.12+) with