为什么在使用AesCryptoServiceProvider第二次解密时，此字符串不相等？

Question

我在C＃（VS2012，.NET 4.5）中加密和解密文本时遇到问题。具体来说，当我加密并随后解密字符串时，输出与输入不同。但是，奇怪的是，如果我复制加密输出并将其硬编码为字符串文字，解密就可以了。以下代码示例说明了该问题。我做错了什么？

var key = new Rfc2898DeriveBytes("test password", Encoding.Unicode.GetBytes("test salt"));
var provider = new AesCryptoServiceProvider { Padding = PaddingMode.PKCS7, KeySize = 256 };
var keyBytes = key.GetBytes(provider.KeySize >> 3);
var ivBytes = key.GetBytes(provider.BlockSize >> 3);
var encryptor = provider.CreateEncryptor(keyBytes, ivBytes);
var decryptor = provider.CreateDecryptor(keyBytes, ivBytes);

var testStringBytes = Encoding.Unicode.GetBytes("test string");
var testStringEncrypted = Convert.ToBase64String(encryptor.TransformFinalBlock(testStringBytes, 0, testStringBytes.Length));

//Prove that the encryption has resulted in the following string
Debug.WriteLine(testStringEncrypted == "cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc="); //Result: True

//Decrypt the encrypted text from a hardcoded string literal
var encryptedBytes = Convert.FromBase64String("cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc=");
var testStringDecrypted = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));

//Decrypt the encrypted text from the string result of the encryption process
var encryptedBytes2 = Convert.FromBase64String(testStringEncrypted);
var testStringDecrypted2 = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes2, 0, encryptedBytes2.Length));

//encryptedBytes and encryptedBytes2 should be identical, so they should result in the same decrypted text - but they don't: 
Debug.WriteLine(testStringDecrypted == "test string"); //Result: True
Debug.WriteLine(testStringDecrypted2 == "test string"); //Result: FALSE
//testStringDecrypted2 is now "૱﷜ୱᵪ㭈盐æing". Curiously, the last three letters are the same.
//WTF?

Answer 1

这似乎是您使用您的线引用的ICryptoTransform的.NET .NET框架实现中的错误：

provider.CreateDecryptor(keyBytes, ivBytes);

为CanReuseTransform返回true但是在解密后似乎没有清除输入缓冲区。有一些解决方案可以让它发挥作用。

选项1 创建第二个解密器并使用该解密器解密第二个字符串。

var key = new Rfc2898DeriveBytes("test password", Encoding.Unicode.GetBytes("test salt"));
var provider = new AesCryptoServiceProvider { Padding = PaddingMode.PKCS7, KeySize = 256 };
var keyBytes = key.GetBytes(provider.KeySize >> 3);
var ivBytes = key.GetBytes(provider.BlockSize >> 3);
var encryptor = provider.CreateEncryptor(keyBytes, ivBytes);
var decryptor = provider.CreateDecryptor(keyBytes, ivBytes);
var decryptor2 = provider.CreateDecryptor(keyBytes, ivBytes);

var testStringBytes = Encoding.Unicode.GetBytes("test string");
var testStringEncrypted = Convert.ToBase64String(encryptor.TransformFinalBlock(testStringBytes, 0, testStringBytes.Length));

//Prove that the encryption has resulted in the following string
Console.WriteLine(testStringEncrypted == "cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc="); //Result: True

//Decrypt the encrypted text from a hardcoded string literal
var encryptedBytes = Convert.FromBase64String("cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc=");

var testStringDecrypted = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));

//Decrypt the encrypted text from the string result of the encryption process
var encryptedBytes2 = Convert.FromBase64String(testStringEncrypted);

var testStringDecrypted2 = Encoding.Unicode.GetString(decryptor2.TransformFinalBlock(encryptedBytes2, 0, encryptedBytes2.Length));

//encryptedBytes and encryptedBytes2 should be identical, so they should result in the same decrypted text - but they don't: 
Console.WriteLine(testStringDecrypted == "test string"); //Result: True
Console.WriteLine(testStringDecrypted2 == "test string"); //Result: True

Console.Read();

选项2 使用RijandaelManaged（或AesManaged）代替AesCryptoServiceProvider，它应该是相同的算法（尽管AesCryptoServiceProvider和AesManaged都将块大小限制为128）

var key = new Rfc2898DeriveBytes("test password", Encoding.Unicode.GetBytes("test salt"));
var provider = new RijndaelManaged { Padding = PaddingMode.PKCS7, KeySize = 256 };
var keyBytes = key.GetBytes(provider.KeySize >> 3);
var ivBytes = key.GetBytes(provider.BlockSize >> 3);
var encryptor = provider.CreateEncryptor(keyBytes, ivBytes);
var decryptor = provider.CreateDecryptor(keyBytes, ivBytes);

var testStringBytes = Encoding.Unicode.GetBytes("test string");
var testStringEncrypted = Convert.ToBase64String(encryptor.TransformFinalBlock(testStringBytes, 0, testStringBytes.Length));

//Prove that the encryption has resulted in the following string
Console.WriteLine(testStringEncrypted == "cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc="); //Result: True

//Decrypt the encrypted text from a hardcoded string literal
var encryptedBytes = Convert.FromBase64String("cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc=");

var testStringDecrypted = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));

//Decrypt the encrypted text from the string result of the encryption process
var encryptedBytes2 = Convert.FromBase64String(testStringEncrypted);

var testStringDecrypted2 = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes2, 0, encryptedBytes2.Length));

//encryptedBytes and encryptedBytes2 should be identical, so they should result in the same decrypted text - but they don't: 
Console.WriteLine(testStringDecrypted == "test string"); //Result: True
Console.WriteLine(testStringDecrypted2 == "test string"); //Result: True

Console.Read();

选项3：改为使用using语句

var key = new Rfc2898DeriveBytes("test password", Encoding.Unicode.GetBytes("test salt"));
var provider = new AesCryptoServiceProvider { Padding = PaddingMode.PKCS7, KeySize = 256 };
var keyBytes = key.GetBytes(provider.KeySize >> 3);
var ivBytes = key.GetBytes(provider.BlockSize >> 3);
var encryptor = provider.CreateEncryptor(keyBytes, ivBytes);

var testStringBytes = Encoding.Unicode.GetBytes("test string");
var testStringEncrypted = Convert.ToBase64String(encryptor.TransformFinalBlock(testStringBytes, 0, testStringBytes.Length));

//Prove that the encryption has resulted in the following string
Console.WriteLine(testStringEncrypted == "cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc="); //Result: True

//Decrypt the encrypted text from a hardcoded string literal
var encryptedBytes = Convert.FromBase64String("cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc=");

string testStringDecrypted, testStringDecrypted2;

using (var decryptor = provider.CreateDecryptor(keyBytes, ivBytes))
{
    testStringDecrypted =
        Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));
}

//Decrypt the encrypted text from the string result of the encryption process
var encryptedBytes2 = Convert.FromBase64String(testStringEncrypted);

using (var decryptor = provider.CreateDecryptor(keyBytes, ivBytes))
{
    testStringDecrypted2 =
        Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes2, 0, encryptedBytes2.Length));
}

//encryptedBytes and encryptedBytes2 should be identical, so they should result in the same decrypted text - but they don't: 
Console.WriteLine(testStringDecrypted == "test string"); //Result: True
Console.WriteLine(testStringDecrypted2 == "test string"); //Result: True

Console.Read();

Answer 2

即使您在两种情况下都使用相同的输入，问题是decryptor.TransformFinalBlock（）的行为在第一次调用后会发生变化。值是否在字符串文字或变量中没有区别。此页面似乎表明解密器在第一次使用后将其“重置”为某个初始状态：

http://www.pcreview.co.uk/forums/icryptotransform-transformfinalblock-behavior-bug-t1233029.html

似乎你可以通过重新调用provider.CreateDecryptor(keyBytes, ivBytes)来为你想要做的每个解密获得一个新的解密器来解决这个问题：

        //Decrypt the encrypted text from a hardcoded string literal
        var encryptedBytes = Convert.FromBase64String("cc1zurZinx4yxeSB0XDzVziEUNJlFXsLzD2p9TWnxEc=");
        var testStringDecrypted = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));

        decryptor = provider.CreateDecryptor(keyBytes, ivBytes);

        //Decrypt the encrypted text from the string result of the encryption process
        var encryptedBytes2 = Convert.FromBase64String(testStringEncrypted);
        var testStringDecrypted2 = Encoding.Unicode.GetString(decryptor.TransformFinalBlock(encryptedBytes2, 0, encryptedBytes2.Length));

Answer 3

我会假设，正如评论中所提到的那样，这是一个重用解密器的问题，它可能仍然在其状态的某个地方有第一个解密的最后一个块，所以它不是从头开始，而是你得到的奇怪的结果。

前几天我实际上不得不写一个AES字符串加密器/解密器，我在这里已经包含了单元测试（需要Xunit）。

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using Xunit;

public interface IStringEncryptor {
    string EncryptString(string plainText);
    string DecryptString(string encryptedText);
}

public class AESStringEncryptor : IStringEncryptor {
    private readonly Encoding _encoding;
    private readonly byte[] _key;
    private readonly Rfc2898DeriveBytes _passwordDeriveBytes;
    private readonly byte[] _salt;

    /// <summary>
    /// Overload of full constructor that uses UTF8Encoding as the default encoding.
    /// </summary>
    /// <param name="key"></param>
    /// <param name="salt"></param>
    public AESStringEncryptor(string key, string salt)
        : this(key, salt, new UTF8Encoding()) {
    }

    public AESStringEncryptor(string key, string salt, Encoding encoding) {
        _encoding = encoding;
        _passwordDeriveBytes = new Rfc2898DeriveBytes(key, _encoding.GetBytes(salt));
        _key = _passwordDeriveBytes.GetBytes(32);
        _salt = _passwordDeriveBytes.GetBytes(16);
    }

    /// <summary>
    /// Encrypts any string to a Base64 string
    /// </summary>
    /// <param name="plainText"></param>
    /// <exception cref="ArgumentNullException">String to encrypt cannot be null or empty.</exception>
    /// <returns>A Base64 string representing the encrypted version of the plainText</returns>
    public string EncryptString(string plainText) {
        if (string.IsNullOrEmpty(plainText)) {
            throw new ArgumentNullException("plainText");
        }

        using (var alg = new RijndaelManaged { BlockSize = 128, FeedbackSize = 128, Key = _key, IV = _salt })
        using (var ms = new MemoryStream())
        using (var cs = new CryptoStream(ms, alg.CreateEncryptor(), CryptoStreamMode.Write)) {
            var plainTextBytes = _encoding.GetBytes(plainText);

            cs.Write(plainTextBytes, 0, plainTextBytes.Length);
            cs.FlushFinalBlock();

            return Convert.ToBase64String(ms.ToArray());
        }
    }

    /// <summary>
    /// Decrypts a Base64 string to the original plainText in the given Encoding
    /// </summary>
    /// <param name="encryptedText">A Base64 string representing the encrypted version of the plainText</param>
    /// <exception cref="ArgumentNullException">String to decrypt cannot be null or empty.</exception>
    /// <exception cref="CryptographicException">Thrown if password, salt, or encoding is different from original encryption.</exception>
    /// <returns>A string encoded</returns>
    public string DecryptString(string encryptedText) {
        if (string.IsNullOrEmpty(encryptedText)) {
            throw new ArgumentNullException("encryptedText");
        }

        using (var alg = new RijndaelManaged { BlockSize = 128, FeedbackSize = 128, Key = _key, IV = _salt })
        using (var ms = new MemoryStream())
        using (var cs = new CryptoStream(ms, alg.CreateDecryptor(), CryptoStreamMode.Write)) {
            var encryptedTextBytes = Convert.FromBase64String(encryptedText);

            cs.Write(encryptedTextBytes, 0, encryptedTextBytes.Length);
            cs.FlushFinalBlock();

            return _encoding.GetString(ms.ToArray());
        }
    }
}

public class AESStringEncryptorTest {
    private const string Password = "TestPassword";
    private const string Salt = "TestSalt";

    private const string Plaintext = "This is a test";

    [Fact]
    public void EncryptionAndDecryptionWorkCorrectly() {
        var aesStringEncryptor = new AESStringEncryptor(Password, Salt);

        string encryptedText = aesStringEncryptor.EncryptString(Plaintext);

        Assert.NotEqual(Plaintext, encryptedText);

        var aesStringDecryptor = new AESStringEncryptor(Password, Salt);

        string decryptedText = aesStringDecryptor.DecryptString(encryptedText);

        Assert.Equal(Plaintext, decryptedText);
    }

    [Fact]
    public void EncodingsWorkWhenSame()
    {
        var aesStringEncryptor = new AESStringEncryptor(Password, Salt, Encoding.ASCII);

        string encryptedText = aesStringEncryptor.EncryptString(Plaintext);

        Assert.NotEqual(Plaintext, encryptedText);

        var aesStringDecryptor = new AESStringEncryptor(Password, Salt, Encoding.ASCII);

        string decryptedText = aesStringDecryptor.DecryptString(encryptedText);

        Assert.Equal(Plaintext, decryptedText);
    }

    [Fact]
    public void EncodingsFailWhenDifferent() {
        var aesStringEncryptor = new AESStringEncryptor(Password, Salt, Encoding.UTF32);

        string encryptedText = aesStringEncryptor.EncryptString(Plaintext);

        Assert.NotEqual(Plaintext, encryptedText);

        var aesStringDecryptor = new AESStringEncryptor(Password, Salt, Encoding.UTF8);

        Assert.Throws<CryptographicException>(() => aesStringDecryptor.DecryptString(encryptedText));
    }

    [Fact]
    public void EncryptionAndDecryptionWithWrongPasswordFails()
    {
        var aes = new AESStringEncryptor(Password, Salt);

        string encryptedText = aes.EncryptString(Plaintext);

        Assert.NotEqual(Plaintext, encryptedText);

        var badAes = new AESStringEncryptor(Password.ToLowerInvariant(), Salt);

        Assert.Throws<CryptographicException>(() => badAes.DecryptString(encryptedText));
    }

    [Fact]
    public void EncryptionAndDecryptionWithWrongSaltFails()
    {
        var aes = new AESStringEncryptor(Password, Salt);

        string encryptedText = aes.EncryptString(Plaintext);

        Assert.NotEqual(Plaintext, encryptedText);

        var badAes = new AESStringEncryptor(Password, Salt.ToLowerInvariant());

        Assert.Throws<CryptographicException>(() => badAes.DecryptString(encryptedText));
    }
}