private static bool VerifyDsaSignature(EncryptedFile file, BinaryReader reader, RSAParameters key)
{
var hasher = Helpers.GetHasherFromCode(file.HasherCode);
reader.BaseStream.Position = 0;
byte[] header = reader.ReadBytes(file.HeaderLength);
var contentHashAggregate = hasher.ComputeHash(header);
byte[] additionalData = reader.ReadBytes(16);
contentHashAggregate = hasher.ComputeHash(contentHashAggregate.Concat(hasher.ComputeHash(additionalData)).ToArray());
for (int i = 0; i < file.NumberOfBlocks; i++)
{
byte[] blockSizeArray = reader.ReadBytes(4);
int blockSize = BitConverter.ToInt32(blockSizeArray, 0);
byte[] block = reader.ReadBytes(blockSize);
contentHashAggregate = hasher.ComputeHash(contentHashAggregate.Concat(hasher.ComputeHash(blockSizeArray.Concat(block).ToArray())).ToArray());
}
int rsaLength = BitConverter.ToInt32(reader.ReadBytes(4), 0);
byte[] rsaSignature = reader.ReadBytes(rsaLength);
return(new RsaMachine(key).CheckSignature(contentHashAggregate, hasher, rsaSignature));
}
/// <summary>
/// This method will parse the <see cref="Stream"/> of the encrypted file.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> of the encrypted file.</param>
/// <returns><see cref="EncryptedFile"/> populated with all the header information required for decryption.</returns>
public static EncryptedFile Parse(Stream stream)
{
BinaryReader reader = new BinaryReader(stream);
EncryptedFile file = new EncryptedFile(reader.BaseStream);
reader.BaseStream.Position = 0;
if (!reader.ReadBytes(6).SequenceEqual(Helpers.MagicBytes))
{
throw new InvalidFileException();
}
file.CryptorCode = Encoding.ASCII.GetString(reader.ReadBytes(Helpers.CryptorCodenameSize));
if (!file.CryptorCode.Equals(AesMachine.Signature) && !file.CryptorCode.Equals(TDesMachine.Signature) && !file.CryptorCode.Equals(TwofishMachine.Signature))
{
throw new UnknownCryptorCodeException(file.CryptorCode);
}
file.HasherCode = Encoding.ASCII.GetString(reader.ReadBytes(Helpers.HasherCodenameSize));
if (!Helpers.IsHasherCodeValid(file.HasherCode))
{
throw new UnknownHasherCodeException(file.HasherCode);
}
int cryptedKeyLength = BitConverter.ToInt32(reader.ReadBytes(4), 0);
file.EncryptedKey = reader.ReadBytes(cryptedKeyLength);
int extLength = BitConverter.ToInt32(reader.ReadBytes(4), 0);
file.FormatExtension = Encoding.ASCII.GetString(reader.ReadBytes(extLength));
file.NumberOfBlocks = BitConverter.ToInt64(reader.ReadBytes(8), 0);
reader.BaseStream.Position += 16;
for (int i = 0; i < file.NumberOfBlocks + 1; i++)
{
int blockSize = BitConverter.ToInt32(reader.ReadBytes(4), 0);
reader.BaseStream.Position += blockSize;
}
if (!(reader.BaseStream.Position == reader.BaseStream.Length))
{
throw new InvalidFileException();
}
return(file);
}
/// <summary>
/// Decrypts a file.
/// </summary>
/// <param name="input"><see cref="EncryptedFile"/> that will be decrypted.</param>
/// <param name="output">Output <see cref="Stream"/> where the decrypted file will be written.</param>
/// <param name="reportProgress">Action that is used to report progress of decryption in percentages.</param>
public void Decrypt(EncryptedFile input, Stream output, Action <int> reportProgress = null)
{
BinaryReader reader = new BinaryReader(input.BaseStream);
reader.BaseStream.Position = input.HeaderLength;
output.Position = 0;
BinaryWriter outputWriter = new BinaryWriter(output);
byte[] decryptedAlgKey = new RsaMachine(this.Key).Decrypt(input.EncryptedKey);
reportProgress?.Invoke(35);
IMachine decryptor = null;
if (input.CryptorCode == AesMachine.Signature)
{
decryptor = new AesMachine(decryptedAlgKey, reader.ReadBytes(16));
}
else if (input.CryptorCode == TDesMachine.Signature)
{
decryptor = new TDesMachine(decryptedAlgKey, reader.ReadBytes(16));
}
else if (input.CryptorCode == TwofishMachine.Signature)
{
decryptor = new TwofishMachine(decryptedAlgKey, reader.ReadBytes(16));
}
for (int i = 0; i < input.NumberOfBlocks; i++)
{
int currentBlockSize = BitConverter.ToInt32(reader.ReadBytes(4), 0);
byte[] block = reader.ReadBytes(currentBlockSize);
outputWriter.Write(decryptor.Decrypt(block));
reportProgress?.Invoke((int)(((float)i / (float)input.NumberOfBlocks) * 1000.00));
}
reportProgress?.Invoke(1000);
}
/// <summary>
/// This method will verify the signature of the encrypted file.
/// </summary>
/// <param name="file">The <see cref="EncryptedFile"/> whose signature will be verified.</param>
/// <param name="param">Public key of the sender.</param>
/// <returns>Boolean indicating if the signature is valid.</returns>
public static bool VerifySignature(EncryptedFile file, RSAParameters param)
{
BinaryReader reader = new BinaryReader(file.BaseStream);
return(VerifyDsaSignature(file, reader, param));
}
