Signing a string with an RSA key in Python - how can I translate this JavaScript code that uses SubtleCrypto to Python?

Question

I am trying to sign a string with an RSA key in Python. I have working JavaScript code that does it, but now I need to replicate it in Python using Python-RSA.

In particular, these are the two JavaScript calls that I need to deal with:

const key = await crypto.subtle.importKey(
'raw',
bytesOfSecretKey,
{ name: 'HMAC', hash: 'SHA-256' },
false,
['sign']);

and

const mac = await crypto.subtle.sign('HMAC', key, bytesOfStringToSign));

where bytesOfSecretKey is just a key string represented as bytes, and bytesOfStringToSign is the string I am signing. Any pointers would be appreciated!

The JavaScript code does not use RSA for signing, but an HMAC. The latter is supported e.g. by the Python standard library (s. hmac). Python-RSA is not required for this (and afaik does not even provide this functionality). — Topaco
– Topaco, Commented Jan 8, 2023 at 20:44
@Topaco Thanks man, that's exactly it. Got it to work with signature = hmac.new(key.encode("utf-8"), str.encode("utf-8"), hashlib.sha256).hexdigest() — PlinyTheElder
– PlinyTheElder, Commented Jan 8, 2023 at 23:08

PlinyTheElder · Accepted Answer · 2023-01-08 23:17:02Z

1

As pointed out by the commenter, the JavaScript code uses HMAC to generate the signature. In python the equivalent code to generate the hexadecimal signature would be:

import hmac
import hashlib

key = 'SECRET_KEY_STRING'
strToSign = 'STRING_TO_SIGN'

signature = hmac.new(key.encode("utf-8"),
                     strToSign.encode("utf-8"), hashlib.sha256).hexdigest()

answered Jan 8, 2023 at 23:17

PlinyTheElder

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