CODEWITHSUNDEEP
pythonencryption
Prometheus
Prometheus

Reputation: 33625

Python decrypt signatures with only a public key

A company wants to send me a digital signature i.e this method. I only have the public key. This signature is used to authenticate who it came from AND contains details of the user, which I need.

What I don't understand is how I decrypt the signature with only public key and the signature I'm sent. All can do from the example I can find is verify the signature. Without knowing what the encrypted string is you cannot decrypt. 

from ecdsa import SigningKey, NIST384p
sk = SigningKey.generate(curve=NIST384p)
vk = sk.get_verifying_key()
signature = sk.sign("message")
assert vk.verify(signature, "message")

I'm I misunderstanding or is there a different type of digital signature they are suggesting?

Upvotes: 1

Views: 3651

Answers (1)

Eric Levieil
Eric Levieil

Reputation: 3574

First, you need to use VerifyingKey. (see also @J0HN excellent comment) Something like (source: https://github.com/warner/python-ecdsa):

from ecdsa import VerifyingKey, BadSignatureError
vk = VerifyingKey.from_pem(open("public.pem").read())
message = open("message","rb").read()
sig = open("signature","rb").read()
try:
    vk.verify(sig, message)
    print "good signature"
except BadSignatureError:
    print "BAD SIGNATURE"

Upvotes: 2

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