RSA Signature Mismatch between NodeJS and Python

Question

I have two short scripts and a (sample) private key that are not producing the same results.

secret.key

sign.py (https://repl.it/@DevinRodriguez1/JumboOlivedrabOs)

from Crypto.PublicKey import RSA
from Crypto.Signature import PKCS1_v1_5
from Crypto.Hash import SHA256
from base64 import b64encode

digest = SHA256.new()
digest.update("This is a string!".encode())

key = open("secret.key", "r").read()
rsakey = RSA.importKey(key)
signer = PKCS1_v1_5.new(rsakey)
sign = signer.sign(digest)
signed = b64encode(sign)

print(signed.decode())

Produces g8gdQsV1XNqTLSZ/cqo961DN//wfEEYMOjQDiFJ4tBfznBHPmun3y3opINVNJHBl48jxWmP42d4fxzLuF4OScwF6KV3aDjKZ8SUmjs8V/1Wp+2Oxh3ukeifMHgt0C18j7gc2E5JUblpRJc/pVt1PrD66iFwdYPWzrsZYbeV3xZtLk9smJIrS+AGHTYyoJRtRp4beK+Ir82HyB+sDNt5lQcrXYsj4lqU7yBfwmWlEHt/ptI1xisv1SHCnHFms6YpbVfxOhicHf5P+FOYrwSyQPQUTtgeswVYScnB8mmBUbH+e8j7Eh3k++lAfZY89l9xB7fQLpTrgylKFHGEGaS+l3Q==

sign.js (https://repl.it/@DevinRodriguez1/LooseWrithingStructures)

const crypto = require('crypto');

const readFileSync = require('fs').readFileSync;

let private_key = readFileSync('secret.key').toString();

let digest = crypto.createHash('SHA256').update("This is a string!");

let signed = crypto.createSign('SHA256').update(digest.digest()).sign(private_key, 'base64');

console.log(signed);

Produces pKJQTqOXJPK60xWzzMhR2h1FtLust7Hd5iy9FvlPUIPYrH0N6U+9xv+AnKSRDdaOcLeAfmpZN7Y2Zkvv15Ai0yB/D5K8LZFz9Jgk3w+Tim5+rIJX1590tAu9mWfeN0JCsSFCVYnrNLEKKKwBDpStnx9NKj+oKPs2lSbtUh8fOFHboleN8U0wAvF7rmlZn0W8v+rZ5HnwJ9pe4FxPLjznw8r7iTEh2z/r/6mUGDJNPS7U2i32fbsX9tOYaU7Ce09T29Mi7Wq3vnAnnr9LffpIBXMMgEIda3svURJODWAXIg5eAXJ0393C36qM3RMY68rWYdT1s9jYfzuELLNMJr1ENQ==

I have tried a dozen modules from NPM that have produced the same signature with no luck in matching the original signature from python. What am I missing here?

Thanks.

score 0 · Answer 1 · answered Oct 29 '19 at 16:57

A secure RSA encryption is implemented with an appropriate padding scheme, which includes some randomness. See PKCS#1 or OAEP for more details.

The RSA encryption encrypts message padded with '0's and a string of random bit. In the process, the random string is "hidden" in the ciphertext by cryptographic hashing and XORing. On decryption, the RSA decryption recovers the random string from the ciphertext and use it to recover message. This is why you get different result with for the same text message.

RSA Signature Mismatch between NodeJS and Python

1 Answers1