public static byte[] Decrypt(byte[] data, C25519Key key)
{
var size = data[1] & 127;
var sizeLength = 0;
var hasFieldSize = (data[1] & 128) != 0;
if (hasFieldSize)
{
sizeLength = size;
size = (int)new BigInteger(data.Skip(2).Take(sizeLength).ToArray(), true, true);
}
var step = 2 + sizeLength;
var asymmetricCipher = data.Skip(step).Take(32 * 3).ToArray();
var asymmetricPlain = key.Decrypt(asymmetricCipher);
step += AsymmetricSize;
if (size == 200)
{
return(UnPad32(asymmetricPlain));
}
var symmetricKey = AesSherableKey.Parse(asymmetricPlain);
return(symmetricKey.Decrypt(data.Skip(step).ToArray()));
}
public static byte[] Encrypt(byte[] buffer, ulong tag, C25519Key key)
{
var toAsymmetricEncrypt = Pad32(buffer);
var bufferSymmetric = new byte[0];
if (buffer.Length > 32)
{
var secret = new AesSherableKey();
bufferSymmetric = secret.Encrypt(buffer);
toAsymmetricEncrypt = secret.ToByteArray();
}
var bufferAsymmetric = key.Encrypt(toAsymmetricEncrypt).ToByteArray();
var tagBuffer = BitConverter.GetBytes(tag);
var signature = key.Sign(bufferAsymmetric.Concat(tagBuffer).ToArray()).PadLeft(32 * 3);
var size =
bufferAsymmetric.Length +
tagBuffer.Length +
signature.Length +
bufferSymmetric.Length;
var dimension = DimensionBuffer(size);
var all = new byte[1 + dimension.Length + size];
all[0] = 1; // version #
dimension.CopyTo(all, 1);
var step = dimension.Length + 1;
bufferAsymmetric.CopyTo(all, step);
step += bufferAsymmetric.Length;
tagBuffer.CopyTo(all, step);
step += tagBuffer.Length;
signature.CopyTo(all, step);
step += signature.Length;
bufferSymmetric.CopyTo(all, step);
return(all);
}
public AesSherableKey GenKey(AesKey key) => AesSherableKey.Parse(key.Hash(ToByteArray()));
