Ciphertext error while decrypting checksum

Question

I'm trying to encrypt a sha256 checksum with the public key (key.pub) and decrypt the same using a private key.

But I'm facing the below error. What am I doing wrong ? Thank you !

Error :

File "C:\Users\code\Encrypt.py", line 29, in decrypt_data return decipher.decrypt(data, None).decode() File "C:\Users\code\lib\site-packages\Crypto\Cipher\PKCS1_v1_5.py", line 174, in decrypt raise ValueError("Ciphertext with incorrect length (not %d bytes)" % k) ValueError: Ciphertext with incorrect length (not 384 bytes)

Code:

import hashlib
import base64
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5

def compute_sha256(file_name):
    hash_sha256 = hashlib.sha256()
    with open(file_name, "rb") as f:
        for chunk in iter(lambda: f.read(4096), b""):
            hash_sha256.update(chunk)
    return hash_sha256.hexdigest()
 

def encrypt_data(data):
    with open("C:\\Users\\code\\key.pub", "rb") as k:
        key = RSA.importKey(k.read())

    cipher = Cipher_PKCS1_v1_5.new(key)
    return cipher.encrypt(data.encode())

def decrypt_data(data):
    with open("C:\\Users\\code\\id_rsa", "rb") as k:
        key = RSA.importKey(k.read())

    decipher = Cipher_PKCS1_v1_5.new(key)
    return decipher.decrypt(data, None).decode()

message = compute_sha256("C:\\Users\\code\\test.rpm")
encrypted = encrypt_data(message)
decrypted = decrypt_data(message)

I'm using pycryptodome

key.pub

id_rsa(private key)

Did you want to `decrypt_data(encrypted)`? – JonSG Aug 17 '23 at 16:40 — JonSG, Aug 17 '23 at 16:40

Stéphane Rigaux · Accepted Answer · 2023-08-17T16:46:54.090

you have to decrypt the crypted message ?

original

message = compute_sha256("C:\\Users\\code\\test.rpm")
encrypted = encrypt_data(message)
decrypted = decrypt_data(message)

modified

message = compute_sha256("C:\\Users\\code\\test.rpm")
encrypted = encrypt_data(message)
decrypted = decrypt_data(encrypted)

I regenerate RSA public key and private key ( i didn't use your keys). See portion of code with REF = RSA encryption and decryption in Python

Code

import hashlib
import base64
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5

def compute_sha256(file_name):
    hash_sha256 = hashlib.sha256()
    with open(file_name, "rb") as f:
        for chunk in iter(lambda: f.read(4096), b""):
            hash_sha256.update(chunk)
    return hash_sha256.hexdigest()
 

def encrypt_data(data):
    with open("./key.pub", "rb") as k:
        key = RSA.importKey(k.read())

    ### REF = https://stackoverflow.com/questions/30056762/rsa-encryption-and-decryption-in-python
    ### First, make a key and save it
    key = RSA.generate(2048)
    with open( 'mykey.pem', 'wb' ) as f:
        f.write( key.exportKey( 'PEM' ))

    cipher = Cipher_PKCS1_v1_5.new(key)
    return cipher.encrypt(data.encode())

def decrypt_data(data):
    with open("./id_rsa", "rb") as k:
        key = RSA.importKey(k.read())
    
    ### REF = https://stackoverflow.com/questions/30056762/rsa-encryption-and-decryption-in-python
    with open( 'mykey.pem', 'r' ) as f:
        key = RSA.importKey( f.read() )

    decipher = Cipher_PKCS1_v1_5.new(key)
    return decipher.decrypt(data, None).decode()

message = compute_sha256("./test.rpm")
encrypted = encrypt_data(message)
decrypted = decrypt_data(encrypted)

Ciphertext error while decrypting checksum

1 Answers1