Firmando y verificando datos usando pycrypto (RSA)

Question

Estoy tratando de familiarizarme con el módulo pycrypto, pero la falta de documentación clara dificulta las cosas.

Para empezar, me gustaría entender la firma y verificación de datos. ¿Podría alguien dar un ejemplo de cómo se escribiría esto?

Answer 1

Esta es una versión detallada de la example in the documentation:

import Crypto.Hash.MD5 as MD5 
import Crypto.PublicKey.RSA as RSA 
import Crypto.PublicKey.DSA as DSA 
import Crypto.PublicKey.ElGamal as ElGamal 
import Crypto.Util.number as CUN 
import os 

plaintext = 'The rain in Spain falls mainly on the Plain' 

# Here is a hash of the message 
hash = MD5.new(plaintext).digest() 
print(repr(hash)) 
# '\xb1./J\xa883\x974\xa4\xac\x1e\x1b!\xc8\x11' 

for alg in (RSA, DSA, ElGamal): 
    # Generates a fresh public/private key pair 
    key = alg.generate(384, os.urandom) 

    if alg == DSA: 
     K = CUN.getRandomNumber(128, os.urandom) 
    elif alg == ElGamal: 
     K = CUN.getPrime(128, os.urandom) 
     while CUN.GCD(K, key.p - 1) != 1: 
      print('K not relatively prime with {n}'.format(n=key.p - 1)) 
      K = CUN.getPrime(128, os.urandom) 
     # print('GCD({K},{n})=1'.format(K=K,n=key.p-1)) 
    else: 
     K = '' 

    # You sign the hash 
    signature = key.sign(hash, K) 
    print(len(signature), alg.__name__) 
    # (1, 'Crypto.PublicKey.RSA') 
    # (2, 'Crypto.PublicKey.DSA') 
    # (2, 'Crypto.PublicKey.ElGamal') 

    # You share pubkey with Friend 
    pubkey = key.publickey() 

    # You send message (plaintext) and signature to Friend. 
    # Friend knows how to compute hash. 
    # Friend verifies the message came from you this way: 
    assert pubkey.verify(hash, signature) 

    # A different hash should not pass the test. 
    assert not pubkey.verify(hash[:-1], signature) 

Answer 2

De acuerdo con la documentación en:

https://www.dlitz.net/software/pycrypto/api/current/Crypto.PublicKey.RSA._RSAobj-class.html

no se debe utilizar la función de Crypto.PublicKey.RSA.sign PyCrypto en código real:

Atención: esta función funciona s el descifrado sencillo y primitivo de RSA (libro de texto). En aplicaciones reales, siempre debe usar un relleno criptográfico adecuado y no debe firmar datos directamente con este método. De lo contrario, puede generar vulnerabilidades de seguridad. Se recomienda utilizar los módulos Crypto.Signature.PKCS1_PSS o Crypto.Signature.PKCS1_v1_5 en su lugar.

Terminé usando el RSA module que implementa PKCS1_v1_5. El documentation for signing fue bastante directo. Otros have recommended use M2Crypto.

Answer 3

a continuación es el helper class que creé para realizar todas las funciones necesarias (RSA cifrado, descifrado, firma, verificando la firma & generar nuevas claves)

rsa.py

from Crypto.PublicKey import RSA 
from Crypto.Cipher import PKCS1_OAEP 
from Crypto.Signature import PKCS1_v1_5 
from Crypto.Hash import SHA512, SHA384, SHA256, SHA, MD5 
from Crypto import Random 
from base64 import b64encode, b64decode 

hash = "SHA-256" 

def newkeys(keysize): 
    random_generator = Random.new().read 
    key = RSA.generate(keysize, random_generator) 
    private, public = key, key.publickey() 
    return public, private 

def importKey(externKey): 
    return RSA.importKey(externKey) 

def getpublickey(priv_key): 
    return priv_key.publickey() 

def encrypt(message, pub_key): 
    #RSA encryption protocol according to PKCS#1 OAEP 
    cipher = PKCS1_OAEP.new(pub_key) 
    return cipher.encrypt(message) 

def decrypt(ciphertext, priv_key): 
    #RSA encryption protocol according to PKCS#1 OAEP 
    cipher = PKCS1_OAEP.new(priv_key) 
    return cipher.decrypt(ciphertext) 

def sign(message, priv_key, hashAlg="SHA-256"): 
    global hash 
    hash = hashAlg 
    signer = PKCS1_v1_5.new(priv_key) 
    if (hash == "SHA-512"): 
     digest = SHA512.new() 
    elif (hash == "SHA-384"): 
     digest = SHA384.new() 
    elif (hash == "SHA-256"): 
     digest = SHA256.new() 
    elif (hash == "SHA-1"): 
     digest = SHA.new() 
    else: 
     digest = MD5.new() 
    digest.update(message) 
    return signer.sign(digest) 

def verify(message, signature, pub_key): 
    signer = PKCS1_v1_5.new(pub_key) 
    if (hash == "SHA-512"): 
     digest = SHA512.new() 
    elif (hash == "SHA-384"): 
     digest = SHA384.new() 
    elif (hash == "SHA-256"): 
     digest = SHA256.new() 
    elif (hash == "SHA-1"): 
     digest = SHA.new() 
    else: 
     digest = MD5.new() 
    digest.update(message) 
    return signer.verify(digest, signature) 

Uso Muestra

import rsa 
from base64 import b64encode, b64decode 

msg1 = "Hello Tony, I am Jarvis!" 
msg2 = "Hello Toni, I am Jarvis!" 
keysize = 2048 
(public, private) = rsa.newkeys(keysize) 
encrypted = b64encode(rsa.encrypt(msg1, public)) 
decrypted = rsa.decrypt(b64decode(encrypted), private) 
signature = b64encode(rsa.sign(msg1, private, "SHA-512")) 
verify = rsa.verify(msg1, b64decode(signature), public) 

print(private.exportKey('PEM')) 
print(public.exportKey('PEM')) 
print("Encrypted: " + encrypted) 
print("Decrypted: '%s'" % decrypted) 
print("Signature: " + signature) 
print("Verify: %s" % verify) 
rsa.verify(msg2, b64decode(signature), public)