加密和解密文件-导致“错误数据”

Question

I'm currently working a little object that will help me encrypt a file then decrypt it, and return it as a MemoryStream. However, when I'm decrypting, I keep getting a "Bad data".

"ExceptionMessage": "Bad Data.\ \ ",
"ExceptionType": "System.Security.Cryptography.CryptographicException",

The Class goes as follow

public class SignatureService {
    private readonly DESCryptoServiceProvider _desCryptoServiceProvider;
    private static byte[] _key = { 5, 6, 7, 2, 3, 4, 8, 1 };
    private static byte[] _iv = { 5, 2, 3, 4, 1, 7, 4, 2 };

    public SignatureService () {
        _desCryptoServiceProvider = new DESCryptoServiceProvider();
    }

    public void SaveSignatureOnDisk ( Stream stream ) {
        using ( var fs = new FileStream( "filepath", FileMode.Create, FileAccess.Write ) ) {
            var cryptoStream = new CryptoStream( fs, _desCryptoServiceProvider.CreateEncryptor( _key, _iv ), CryptoStreamMode.Write );
            var bytearrayinput = new byte[ stream.Length - 1 ];
            stream.Read( bytearrayinput, 0, bytearrayinput.Length );
            cryptoStream.Write( bytearrayinput, 0, bytearrayinput.Length );
        }
 }

    public Stream ReadSignatureOnDisk () {
        Stream returnedStream;
        using ( var fs = new FileStream( "filepath", FileMode.Open, FileAccess.Read ) ) {
            var cryptoStream = new CryptoStream( fs, _desCryptoServiceProvider.CreateDecryptor( _key, _iv ), CryptoStreamMode.Read );

            string contents = new StreamReader( cryptoStream ).ReadToEnd();
            byte[] unicodes = Encoding.Unicode.GetBytes( contents );
            returnedStream = new MemoryStream( unicodes );
        }

        return returnedStream;
    }
}

Answer 1

You made a few mistakes, the CryptoStream and the ICryptoTransform from CreateDecryptor and CreateEncryptor should be disposed. Also your stream.Read is not reliable, Read is not guaranteed to actually read all of the bytes you asked it to. You must either loop till the Read returns 0 or use .CopyTo( if you are on a version of .NET that has it.

public void SaveSignatureOnDisk ( Stream stream ) 
{
    using (var fs = new FileStream("filepath", FileMode.Create, FileAccess.Write))
    using (var encryptor = _desCryptoServiceProvider.CreateEncryptor( _key, _iv))
    using (var cryptoStream = new CryptoStream(fs, encryptor, CryptoStreamMode.Write))
    {
        stream.CopyTo(cryptoStream);
    }
}

Your ReadSignatureOnDisk also has the same mistakes and needs to be fixed similarly.

public Stream ReadSignatureOnDisk ()
{
    Stream returnedStream = new MemoryStream();
    using (var fs = new FileStream("filepath", FileMode.Open, FileAccess.Read))
    using (var decryptor = _desCryptoServiceProvider.CreateDecryptor(_key, _iv))
    using (var cryptoStream = new CryptoStream(fs, decryptor, CryptoStreamMode.Read);
    {
        cryptoStream.CopyTo(returnedStream);
    }

    returnedStream.Position = 0
    return returnedStream;
}

If you want you could use my ReturnableCryptoStream class I wrote for another answer which allows you to return the original crypto stream and just let the caller dispose it.

/// <summary>
/// Creates a class that creates a <see cref="CryptoStream"/> and wraps the disposing action of all the associated objects 
/// </summary>
class ReturnableCryptoStream : CryptoStream
{
    private readonly ICryptoTransform _transform;
    private readonly IDisposable _algorithom;

    public ReturnableCryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode, IDisposable algorithom) 
        : base(stream, transform, mode)
    {
        _transform = transform;
        _algorithom = algorithom;
    }

    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);
        if (disposing)
        {
            if (_transform != null)
                _transform.Dispose();

            if (_algorithom != null)
                _algorithom.Dispose();
        }
    }
}

used like

public Stream ReadSignatureOnDisk ()
{
    var fs = new FileStream("filepath", FileMode.Open, FileAccess.Read);
    var serviceProvider = new DESCryptoServiceProvider()
    var decryptor = serviceProvider.CreateDecryptor(_key, _iv);
    var cryptoStream = new ReturnableCryptoStream(fs, 
             decryptor, 
             CryptoStreamMode.Read, 
             serviceProvider); 
    //note that I now make my own local copy of the service provider, you could use your 
    //existing one and pass in null to the ReturnableCryptoStream.

    return cryptoStream ;
}