internal static void key_derive(byte[] shared, byte[] salt, byte[] secretKey, byte[] pubkey)
{
var longKeyHash = new byte[64];
var shortKeyHash = new byte[32];
Array.Reverse(secretKey);
// compute Sha3(512) hash of secret key (as in prepareForScalarMultiply)
var digestSha3 = new KeccakDigest(512);
digestSha3.BlockUpdate(secretKey, 0, 32);
digestSha3.DoFinal(longKeyHash, 0);
longKeyHash[0] &= 248;
longKeyHash[31] &= 127;
longKeyHash[31] |= 64;
Array.Copy(longKeyHash, 0, shortKeyHash, 0, 32);
ScalarOperations.sc_clamp(shortKeyHash, 0);
var p = new[] { new long[16], new long[16], new long[16], new long[16] };
var q = new[] { new long[16], new long[16], new long[16], new long[16] };
TweetNaCl.Unpackneg(q, pubkey); // returning -1 invalid signature
TweetNaCl.Scalarmult(p, q, shortKeyHash, 0);
TweetNaCl.Pack(shared, p);
// for some reason the most significant bit of the last byte needs to be flipped.
// doesnt seem to be any corrosponding action in nano/nem.core, so this may be an issue in one of the above 3 functions. i have no idea.
shared[31] ^= (1 << 7);
// salt
for (var i = 0; i < salt.Length; i++)
{
shared[i] ^= salt[i];
}
// hash salted shared key
var digestSha3Two = new KeccakDigest(256);
digestSha3Two.BlockUpdate(shared, 0, 32);
digestSha3Two.DoFinal(shared, 0);
}