Rijndael文件加密/解密

Question

在过去的几天里，我基于RijndaelManaged类中可用的Rijndael加密标准创建了一个文件加密/解密类，并浏览了我可以找到的所有资源和示例。这些例子要么是过时的，要么是破碎的，要么是有限的，但至少已经学到了很多东西，我认为我会在确保它的强大性和超越你的批评之后，发布一个最新版本的。

到目前为止，我发现的唯一问题是，需要知道salt无法像字符串那样存储在加密的文件中，除非您将每字节的读/写转换为基于读/写的缓冲区，但是在解密时需要满足这一点，而且还需要至少4字节的数据来加密(虽然我并不认为这是一个问题，但需要提及)。

我也不完全确定，一个盐是否足以满足密钥和初始化向量，还是两个更好的安全原因？

任何其他意见和/或优化也将是非常感谢的。

class FileEncDec
{
    private int keySize;
    private string passPhrase;

    internal FileEncDec( int keySize = 256, string passPhrase = @"This is pass phrase key to use for testing" )
    {
        this.keySize = keySize;
        this.passPhrase = passPhrase; // Can be user selected and must be kept secret
    }

    private static byte[] GenerateSalt( int length )
    {
        byte[] salt = new byte[ length ];

        // Populate salt with cryptographically strong bytes.
        RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();

        rng.GetNonZeroBytes( salt );

        // Split salt length (always one byte) into four two-bit pieces and store these pieces in the first four bytes 
        // of the salt array.
        salt[ 0 ] = (byte)( ( salt[ 0 ] & 0xfc ) | ( length & 0x03 ) );
        salt[ 1 ] = (byte)( ( salt[ 1 ] & 0xf3 ) | ( length & 0x0c ) );
        salt[ 2 ] = (byte)( ( salt[ 2 ] & 0xcf ) | ( length & 0x30 ) );
        salt[ 3 ] = (byte)( ( salt[ 3 ] & 0x3f ) | ( length & 0xc0 ) );

        return salt;
    }

    internal bool EncryptFile( string inputFile, string outputFile )
    {
        try
        {
            byte[] salt = GenerateSalt( 16 ); // Salt needs to be known for decryption (can be safely stored in the file)
            Rfc2898DeriveBytes derivedBytes = new Rfc2898DeriveBytes( passPhrase, salt, 10000 );
            int bytesRead, bufferSize = keySize / 8;
            byte[] data = new byte[ bufferSize ];
            RijndaelManaged cryptor = new RijndaelManaged();
            cryptor.Key = derivedBytes.GetBytes( keySize / 8 );
            cryptor.IV = derivedBytes.GetBytes( cryptor.BlockSize / 8 );

            using ( var fsIn = new FileStream( inputFile, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, FileOptions.SequentialScan ) )
            {
                using ( var fsOut = new FileStream( outputFile, FileMode.Create, FileAccess.Write, FileShare.None, 4096, FileOptions.SequentialScan ) )
                {
                    // Add the salt to the file
                    fsOut.Write( salt, 0, salt.Length );

                    using ( CryptoStream cs = new CryptoStream( fsOut, cryptor.CreateEncryptor(), CryptoStreamMode.Write ) )
                    {
                        while ( ( bytesRead = fsIn.Read( data, 0, bufferSize ) ) > 0 )
                        {
                            cs.Write( data, 0, bytesRead );
                        }
                    }
                }
            }

            return true;
        }
        catch ( Exception )
        {
            return false;
        }
    }

    internal bool DecryptFile( string inputFile, string outputFile )
    {
        try
        {
            int bytesRead = 0, bufferSize = keySize / 8, saltLen;
            byte[] data = new byte[ bufferSize ], salt;
            Rfc2898DeriveBytes derivedBytes;
            RijndaelManaged cryptor = new RijndaelManaged();    // Create new cryptor so it's thread safe and don't need to use locks

            using ( var fsIn = new FileStream( inputFile, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, FileOptions.SequentialScan ) )
            {
                // Retrieve the salt length from the file
                fsIn.Read( data, 0, 4 );

                saltLen =   ( data[ 0 ] & 0x03 ) |
                            ( data[ 1 ] & 0x0c ) |
                            ( data[ 2 ] & 0x30 ) |
                            ( data[ 3 ] & 0xc0 );

                salt = new byte[ saltLen ];
                Array.Copy( data, salt, 4 );

                // Retrieve the remaining salt from the file and create the cryptor
                fsIn.Read( salt, 4, saltLen - 4 );
                derivedBytes = new Rfc2898DeriveBytes( passPhrase, salt, 10000 );
                cryptor.Key = derivedBytes.GetBytes( keySize / 8 );
                cryptor.IV = derivedBytes.GetBytes( cryptor.BlockSize / 8 );

                using ( var fsOut = new FileStream( outputFile, FileMode.Create, FileAccess.Write, FileShare.None, 4096, FileOptions.SequentialScan ) )
                {
                    using ( var cs = new CryptoStream( fsIn, cryptor.CreateDecryptor(), CryptoStreamMode.Read ) )
                    {
                        while ( ( bytesRead = cs.Read( data, 0, bufferSize ) ) > 0 )
                        {
                            fsOut.Write( data, 0, bytesRead );
                        }
                    }
                }
            }

            return true;
        }
        catch ( Exception )
        {
            return false;
        }
    }
}

编辑: 1.添加盐发生器。2.重构为单salt和Rfc2898DerivedBytes，从password + salt推导出IV。3.使加密/解密线程安全(如果我做错了，请告诉我)。

编辑2: 1.重构，使读/写使用缓冲区，而不是单字节读/写。2.在加密文件中嵌入salt并清除变量(但仍然允许passPhrase默认为“复制/粘贴”示例)。3.重构文件句柄。

Answer 1

你应该每次都用不同的静脉输液。如果您使用相同的IV与相同的数据，结果是相同的。攻击者现在可以推断文件(部分)是相同的，这是一个漏洞。您可以生成16个强随机字节，并将它们用作Rfc2898DeriveBytes的salt。将这些字节准备到文件中。只使用一个Rfc2898DeriveBytes来生成IV和key。或者，您可以对密钥完全不使用salt，并随机生成IV。salt可用于使密钥派生对您的用例而言是唯一的，或者例如，为应用程序的每个用户提供不同的密钥派生算法。

注意，按字节顺序处理流的速度非常慢。使用缓冲器。也许，您应该使用Stream.Copy。