How to generate a digital signature of a string in Python?

Question

I have a string and I need to generate a digital signature for it using my private key? How can I do it in Python?

Answer 1

You could use the Cryptography module to generate a private key then sign your string using RSA:

# Generate a private key   
>>> from cryptography.hazmat.backends import default_backend
>>> from cryptography.hazmat.primitives.asymmetric import rsa
>>> private_key = rsa.generate_private_key(
...     public_exponent=65537,
...     key_size=2048,
...     backend=default_backend()
... )

# Sign a message using the key
>>> from cryptography.hazmat.primitives import hashes
>>> from cryptography.hazmat.primitives.asymmetric import padding
>>> message = b"A message I want to sign"
>>> signature = private_key.sign(
...     message,
...     padding.PSS(
...         mgf=padding.MGF1(hashes.SHA256()),
...         salt_length=padding.PSS.MAX_LENGTH
...     ),
...     hashes.SHA256()
... )

If you already have a private key that you want to use, then you can load it rather than generating a new one.