/// <summary>
/// Creates a symmetric decryptor object with the current Key property and one-time use state parameter.
/// </summary>
/// <param name="key">The secret that will be used during decryption.</param>
/// <param name="nonce">The one-time use state parameter.</param>
public override ICryptoTransform CreateDecryptor(byte[] key, byte[] nonce)
{
var ivLow = m_iv;
var ivHigh = BinaryPrimitives.ReadUInt32LittleEndian(nonce.AsSpan(0, ChaChaTransform.WordLength));
return(ChaChaTransform.New(Initialize(key, nonce, ivLow), BitwiseHelpers.ConcatBits(ivHigh, ivLow), 20U));
}
private void Compress(ReadOnlySpan <byte> data, uint finalizer)
{
var dataAsUInt = MemoryMarshal.Cast <byte, uint>(data);
var h0 = m_h0;
var h1 = m_h1;
var h2 = m_h2;
var h3 = m_h3;
var h4 = m_h4;
var r0 = m_r0;
var r1 = m_r1;
var r2 = m_r2;
var r3 = m_r3;
var r4 = m_r4;
var s0 = m_s0;
var s1 = m_s1;
var s2 = m_s2;
var s3 = m_s3;
var t0 = dataAsUInt[0];
var t1 = dataAsUInt[1];
var t2 = dataAsUInt[2];
var t3 = dataAsUInt[3];
h0 += (t0 & 0x3FFFFFFU);
h1 += ((uint)((BitwiseHelpers.ConcatBits(t1, t0) >> 26) & 0x3FFFFFFU));
h2 += ((uint)((BitwiseHelpers.ConcatBits(t2, t1) >> 20) & 0x3FFFFFFU));
h3 += ((uint)((BitwiseHelpers.ConcatBits(t3, t2) >> 14) & 0x3FFFFFFU));
h4 += ((uint)BitwiseHelpers.Add((t3 >> 8), finalizer));
var d0 = (BitwiseHelpers.Multiply(h0, r0) + BitwiseHelpers.Multiply(h1, s3) + BitwiseHelpers.Multiply(h2, s2) + BitwiseHelpers.Multiply(h3, s1) + BitwiseHelpers.Multiply(h4, s0));
var d1 = (BitwiseHelpers.Multiply(h0, r1) + BitwiseHelpers.Multiply(h1, r0) + BitwiseHelpers.Multiply(h2, s3) + BitwiseHelpers.Multiply(h3, s2) + BitwiseHelpers.Multiply(h4, s1));
var d2 = (BitwiseHelpers.Multiply(h0, r2) + BitwiseHelpers.Multiply(h1, r1) + BitwiseHelpers.Multiply(h2, r0) + BitwiseHelpers.Multiply(h3, s3) + BitwiseHelpers.Multiply(h4, s2));
var d3 = (BitwiseHelpers.Multiply(h0, r3) + BitwiseHelpers.Multiply(h1, r2) + BitwiseHelpers.Multiply(h2, r1) + BitwiseHelpers.Multiply(h3, r0) + BitwiseHelpers.Multiply(h4, s3));
var d4 = (BitwiseHelpers.Multiply(h0, r4) + BitwiseHelpers.Multiply(h1, r3) + BitwiseHelpers.Multiply(h2, r2) + BitwiseHelpers.Multiply(h3, r1) + BitwiseHelpers.Multiply(h4, r0));
var c = (d0 >> 26);
h0 = ((uint)(d0 & 0x3FFFFFFU));
d1 += c;
c = (d1 >> 26);
h1 = ((uint)(d1 & 0x3FFFFFFU));
d2 += c;
c = (d2 >> 26);
h2 = ((uint)(d2 & 0x3FFFFFFU));
d3 += c;
c = (d3 >> 26);
h3 = ((uint)(d3 & 0x3FFFFFFU));
d4 += c;
c = (d4 >> 26);
h4 = ((uint)(d4 & 0x3FFFFFFU));
h0 += ((uint)(c * 5UL));
c = (h0 >> 26);
h0 = (h0 & 0x3FFFFFFU);
h1 += ((uint)c);
m_h0 = h0;
m_h1 = h1;
m_h2 = h2;
m_h3 = h3;
m_h4 = h4;
}
public static byte[] GenerateOneTimeKey(ReadOnlySpan <byte> key, ReadOnlySpan <byte> nonce, uint numRounds)
{
var ivLow = 0U;
var ivHigh = BinaryPrimitives.ReadUInt32LittleEndian(nonce);
var oneTimeKey = new byte[ChaChaTransform.BlockLength];
ChaChaTransform.WriteKeyStreamBlock(ChaCha.Initialize(key, nonce, ivLow), BitwiseHelpers.ConcatBits(ivHigh, ivLow), numRounds, oneTimeKey);
return(oneTimeKey);
}