Lamport signature

[James-E-A]

Is support for Lamport signatures something you'd be interested in adding to the scope of this library?

It's a one-time signature scheme using a hash function as its primitive, and is a necessary cryptographic "building block" for recent linkable ring signature schemes, such as Lu, Au, and Zhang (2019).

>>> from Crypto.PublicKey import Lamport
>>> secret_key = Lamport.generate(512)
>>> public_key = secret_key.publickey()
>>> signature = secret_key.sign("This message has been one-time-signed!".encode())
>>> public_key.verify("This message has been one-time-signed!".encode(), signature)
True
>>> public_key.verify("This message has been one-time-singed!".encode(), signature)
False

[James-E-A]

1fdfa3a adds the following behavior:

>>> from Crypto.PublicKey import Lamport
>>> secret_key = Lamport.generate(512)
>>> public_key = secret_key.publickey()
>>> signature = secret_key.sign("This message has been one-time-signed!".encode())
>>> signatoor = secret_key.sign("This message has been two-time-signed!".encode())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/sweg/.local/lib/python3.8/site-packages/Crypto/PublicKey/Lamport.py", line 73, in sign
    return self._sign(self._h(message))
  File "/home/sweg/.local/lib/python3.8/site-packages/Crypto/PublicKey/Lamport.py", line 66, in _sign
    raise RuntimeError("This key has already been used!")
RuntimeError: This key has already been used!

[James-E-A]

Would PKCS8 import and export be a useful or appropriate feature for this? I've got it half coded so far.

[James-E-A]

Hmm, if added, this is a niche/research-focused item, so I suppose it'd belong in the experimental module

[James-E-A]

Upon further consideration, this truly is too research-focused for inclusion in a general-purpose cryptography library