Random number generation

When generating random data for use in cryptographic operations, such as an initialization vector for encryption in CBC mode, you do not want to use the standard random module APIs. This is because they do not provide a cryptographically secure random number generator, which can result in major security issues depending on the algorithms in use.

Therefore, it is our recommendation to always use your operating system’s provided random number generator, which is available as os.urandom(). For example, if you need 16 bytes of random data for an initialization vector, you can obtain them with:

>>> import os
>>> iv = os.urandom(16)

This will use /dev/urandom on UNIX platforms, and CryptGenRandom on Windows.

If you need your random number as an integer (for example, for serial_number()), you can use int.from_bytes to convert the result of os.urandom:

>>> serial = int.from_bytes(os.urandom(20), byteorder="big")

In addition, the Python standard library includes the secrets module, which can be used for generating cryptographically secure random numbers, with specific helpers for text-based formats.