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.我究竟做错了什么？

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 "???????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框架实现中的错误:

provider.CreateDecryptor(keyBytes, ivBytes);

对CanReuseTransform返回true 但是在解密后它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();