generateSecret function

BigInt generateSecret(BigInt q, BigInt x, List<int> hash)

Implementation

BigInt generateSecret(BigInt q, BigInt x, List<int> hash) {
  var hasher = sha256;

  var qLen = q.bitLength;
  var hoLen =
      32; // = sha256.size, because the sha256 is fixed here so do the len
  var roLen = (qLen + 7) >> 3;

  var bx = intToOctets(x, roLen) + bitsToOctets(hash, q, roLen);
  var v = List<int>.filled(hoLen, 0x01);
  var k = List<int>.filled(hoLen, 0x00);

  k = Hmac(hasher, k).convert(v + [0x00] + bx).bytes;
  v = Hmac(hasher, k).convert(v).bytes;
  k = Hmac(hasher, k).convert(v + [0x01] + bx).bytes;
  v = Hmac(hasher, k).convert(v).bytes;

  while (true) {
    var t = <int>[];
    while (t.length * 8 < qLen) {
      v = Hmac(hasher, k).convert(v).bytes;
      t = t + v;
    }

    var secret = bitsToInt(t, qLen);
    if (secret >= BigInt.one && secret < q) {
      return secret;
    }

    k = Hmac(hasher, k).convert(v + [0x00]).bytes;
    v = Hmac(hasher, k).convert(v).bytes;
  }
}