/**
* The Elliptic Curve Diffe-Hellman Key Agreement Scheme as specified in ANSI X9.63 and IEEE P1363
* In ECKAS-DH1 (the Elliptic Curve Key Agreement Scheme, Diffie-Hellman 1), each party combines
* its own private key with the other party�fs public key to calculate a shared secret key which
* can then be used as the key for a symmetric encryption algorithm such as AES. Other (public or
* private) information known to both parties may be used as key derivation parameters to ensure
* that a di erent secret key is generated every session. This key agreement scheme is described
* in more detail in section 9.2 of the IEEEP1363 standard. This Calculates a 128 bit secret key
* from EC domain parameters dp, private key s, public key Wi and key derivation parameter P (an
* octet string). s belongs to one party, Wi belongs to the other and dp and P are common to both
* of them.
*
* @param dp The EC domain parameters.
* @param s The EC private key.
* @param Wi The EC public key.
* @param P The key derivation parameter.
* @return
*/
public static BigInteger ECKAS_DH1(ECDomainParameters dp, BigInteger s, ECPoint Wi, int[] P) {
Fq z = ECSVDP_DH(dp, s, Wi);
int[] Z = Utils.FE2OSP(z);
int[] k = KDF2(Z, 16, P); // 128 bits
BigInteger K = Utils.OS2IP(k);
return K;
}
