Rijndael文件加密/解密

Rijndael file encryption / decryption

过去几天,我根据 RijndaelManaged class 可用的 Rijndael 加密标准创建了一个文件加密/解密 class,并搜索了我能找到的所有资源和示例.这些示例不是过时的、损坏的就是有限的,但至少设法学到了很多东西,并且认为我会 post 在确保它是健壮的并且经过您的批评之后我会 post 它的最新版本。

到目前为止我发现的唯一问题是需要知道盐,因为没有办法将它存储在加密文件中,就像您对字符串所做的那样,除非您转换每个字节 read/write 到基于 read/write 的缓冲区,但是你需要在解密时满足它,并且还需要至少 4 个字节的数据来加密(虽然我真的不认为这是一个问题但确实需要被提及)。

我也不完全确定 1 个 salt 是否足以同时满足密钥和初始化向量,或者出于安全原因两个更好?

任何其他意见和/或优化也将不胜感激

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.新增盐发生器。 2. 重构为单个 saltRfc2898DerivedBytes,现在从 password + salt 推导出 IV。 3. 使加密/解密线程安全(如果我做的不正确请告诉我)。

编辑 2: 1. 重构使读/写使用缓冲区而不是单字节读/写。 2. 在加密文件中嵌入盐并清理变量(但仍然允许 passPhrase 默认为 "copy/paste" 示例。 3. 重构文件句柄。

您可能每次都应该使用不同的 IV。如果您对相同的数据使用相同的 IV,则结果是相同的。攻击者现在可以推断出文件(部分)相同,这就是泄漏。您可以生成 16 个强随机字节并将它们用作 Rfc2898DeriveBytes 的盐。将这些字节添加到文件中。仅使用一个 Rfc2898DeriveBytes 来生成 IV 和密钥。或者,您可以完全不对密钥使用盐并随机生成 IV。 salt 可用于使密钥派生对于您的用例是唯一的,或者例如为您的应用程序的每个用户提供不同的密钥派生算法。

请注意,按字节处理流非常慢。使用缓冲区。也许,你应该使用 Stream.Copy.