PullMsgResult ProduceWelcome(ref Msg msg)
{
Span <byte> cookieNonce = stackalloc byte[Curve25519XSalsa20Poly1305.NonceLength];
Span <byte> cookiePlaintext = stackalloc byte[64];
Span <byte> cookieCiphertext = stackalloc byte[64 + XSalsa20Poly1305.TagLength];
// Create full nonce for encryption
// 8-byte prefix plus 16-byte random nonce
CookieNoncePrefix.CopyTo(cookieNonce);
using var rng = RandomNumberGenerator.Create();
#if NETSTANDARD2_1
rng.GetBytes(cookieNonce.Slice(8));
#else
byte[] temp = new byte[16];
rng.GetBytes(temp);
temp.CopyTo(cookieNonce.Slice(8));
#endif
// Generate cookie = Box [C' + s'](t)
m_cnClientKey.CopyTo(cookiePlaintext);
m_cnSecretKey.CopyTo(cookiePlaintext.Slice(32));
// Generate fresh cookie key
rng.GetBytes(m_cookieKey);
// Encrypt using symmetric cookie key
using var secretBox = new XSalsa20Poly1305(m_cookieKey);
secretBox.Encrypt(cookieCiphertext, cookiePlaintext, cookieNonce);
cookiePlaintext.Clear();
Span <byte> welcomeNonce = stackalloc byte[Curve25519XSalsa20Poly1305.NonceLength];
Span <byte> welcomePlaintext = stackalloc byte[128];
Span <byte> welcomeCiphertext = stackalloc byte[128 + Curve25519XSalsa20Poly1305.TagLength];
// Create full nonce for encryption
// 8-byte prefix plus 16-byte random nonce
WelcomeNoncePrefix.CopyTo(welcomeNonce);
#if NETSTANDARD2_1
rng.GetBytes(welcomeNonce.Slice(8));
#else
rng.GetBytes(temp);
temp.CopyTo(welcomeNonce.Slice(8));
#endif
// Create 144-byte Box [S' + cookie](S->C')
m_cnPublicKey.CopyTo(welcomePlaintext);
cookieNonce.Slice(8).CopyTo(welcomePlaintext.Slice(32));
cookieCiphertext.CopyTo(welcomePlaintext.Slice(48));
using var box = new Curve25519XSalsa20Poly1305(m_secretKey, m_cnClientKey);
box.Encrypt(welcomeCiphertext, welcomePlaintext, welcomeNonce);
welcomePlaintext.Clear();
msg.InitPool(168); // TODO: we can save some allocation here by allocating this earlier
Span <byte> welcome = msg;
WelcomeLiteral.CopyTo(welcome);
welcomeNonce.Slice(8, 16).CopyTo(welcome.Slice(8));
welcomeCiphertext.CopyTo(welcome.Slice(24));
return(PullMsgResult.Ok);
}
PushMsgResult ProcessWelcome(ref Msg msg)
{
if (msg.Size != 168)
{
return(PushMsgResult.Error);
}
Span <byte> welcomeNonce = stackalloc byte[Curve25519XSalsa20Poly1305.NonceLength];
Span <byte> welcomePlaintext = stackalloc byte[128];
Span <byte> welcomeBox = msg.Slice(24, 144);
WelcomeNoncePrefix.CopyTo(welcomeNonce);
msg.Slice(8, 16).CopyTo(welcomeNonce.Slice(8));
using var box = new Curve25519XSalsa20Poly1305(m_cnSecretKey, m_serverKey);
bool isDecrypted = box.TryDecrypt(welcomePlaintext, welcomeBox, welcomeNonce);
if (!isDecrypted)
{
return(PushMsgResult.Error);
}
m_cnServerKey = welcomePlaintext.Slice(0, 32).ToArray();
m_cnCookie = welcomePlaintext.Slice(32, 16 + 80).ToArray();
// Create the curve box
m_box = new Curve25519XSalsa20Poly1305(m_cnSecretKey, m_cnServerKey);
m_state = State.SendInitiate;
return(PushMsgResult.Ok);
}