RSA加密SHA256校验和后解密报错：密文长度不正确

错误信息 #

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)

问题代码 #

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)

问题分析 #

• 核心错误：解密参数传错
  调用decrypt_data时传入的是原始的message（SHA256十六进制字符串），而非加密后生成的encrypted二进制数据。你的RSA密钥是3072位（对应384字节），RSA解密要求输入必须是对应密钥长度的加密二进制数据，原始字符串长度远小于该值，因此触发长度错误。
• 额外问题：二进制数据处理
  RSA加密返回的二进制字节流直接存储或打印易出现乱码、数据损坏，建议用Base64编码转为可打印字符串，解密时再解码回二进制。

修正后的代码 #

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)
    # 加密后用Base64编码，避免二进制数据损坏
    encrypted_bytes = cipher.encrypt(data.encode())
    return base64.b64encode(encrypted_bytes).decode()

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)
    # 先Base64解码回二进制
    encrypted_bytes = base64.b64decode(data)
    return decipher.decrypt(encrypted_bytes, None).decode()

message = compute_sha256("C:\\Users\\code\\test.rpm")
encrypted = encrypt_data(message)
decrypted = decrypt_data(encrypted)  # 传入加密后的数据
print(f"原始SHA256: {message}")
print(f"解密后SHA256: {decrypted}")

说明 #

• 修正了解密参数，传入加密后的encrypted数据而非原始字符串；
• 增加Base64编解码处理，确保加密数据可安全传输、存储；
• 运行后会输出原始与解密后的SHA256校验和，验证一致性。

内容的提问来源于stack exchange，提问作者Rafa S