使用Bouncy Castle RSA加解密密码时遇block incorrect错误

注意：请勿使用此方法加密用户密码。应使用哈希算法存储用户密码，还可类似Salt Bae的方式为密码添加盐值。

我需要存储一个用于程序登录的密码，加密操作可正常完成，但解密时出现以下错误：
Org.BouncyCastle.Crypto.InvalidCipherTextException: 'block incorrect'

后续会更换私钥，因此无需担心当前私钥泄露问题。

程序类代码 #

var input = "TestPassword123!";

Encryption EC = new Encryption();

var Key = "-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----";

var encrypted = EC.RsaEncrypt(input, Key);

string password = EC.RsaDecrypt(encrypted, Key);

加密类代码 #

using System;
using System.IO;
using System.Text;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Encodings;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.OpenSsl;

namespace TemarkNamespace
{
    internal class Encryption
    {
        public string RsaEncrypt(string clearText, string Key)
        {
            var bytesToEncrypt = Encoding.UTF8.GetBytes(clearText);

            var encryptEngine = new Pkcs1Encoding(new RsaEngine());

            using (var txtreader = new StringReader(Key))
            {
                var keyPair = (AsymmetricCipherKeyPair)new PemReader(txtreader).ReadObject();

                encryptEngine.Init(true, keyPair.Private);
            }

            var encrypted = Convert.ToBase64String(encryptEngine.ProcessBlock(bytesToEncrypt, 0, bytesToEncrypt.Length));
            return encrypted;
        }

        // Decryption:
        public string RsaDecrypt(string pass, string Key)
        {
            var bytesToDecrypt = Convert.FromBase64String(pass);

            AsymmetricCipherKeyPair keyPair;
            var decryptEngine = new Pkcs1Encoding(new RsaEngine());

            using (var txtreader = new StringReader(Key))
            {
                keyPair = (AsymmetricCipherKeyPair)new PemReader(txtreader).ReadObject();

                decryptEngine.Init(false, keyPair.Private);
            }

            var decrypted = Encoding.UTF8.GetString(decryptEngine.ProcessBlock(bytesToDecrypt, 0, bytesToDecrypt.Length));
            return decrypted;
        }
    }
}

问题原因 #

你犯了RSA使用的核心错误：加密应该用公钥，解密用私钥。当前代码中加密和解密都使用了私钥，虽然用私钥"加密"本质是签名操作，但PKCS#1编码的解密逻辑会验证密文格式，导致抛出"block incorrect"错误。

修复方案 #

修改RsaEncrypt方法，初始化加密引擎时使用公钥（keyPair.Public）而非私钥：

public string RsaEncrypt(string clearText, string Key)
{
    var bytesToEncrypt = Encoding.UTF8.GetBytes(clearText);

    var encryptEngine = new Pkcs1Encoding(new RsaEngine());

    using (var txtreader = new StringReader(Key))
    {
        var keyPair = (AsymmetricCipherKeyPair)new PemReader(txtreader).ReadObject();
        // 替换为使用公钥初始化加密引擎
        encryptEngine.Init(true, keyPair.Public);
    }

    var encrypted = Convert.ToBase64String(encryptEngine.ProcessBlock(bytesToEncrypt, 0, bytesToEncrypt.Length));
    return encrypted;
}

修改后，加密用公钥，解密用私钥，即可正常完成加解密流程。

内容的提问来源于stack exchange，提问作者Meneghini