Explanation/Reference:
Explanation:

Elliptic Curve
Elliptic Curve Cryptography (ECC) is a newer alternative to public key cryptography. ECC operates on
elliptic curves over finite fields. The main advantage of elliptic curves is their efficiency. They can offer the
same level of security for modular arithmetic operations over much smaller prime fields. Thus, the relative
performance of ECC algorithms is significantly better than traditional public key cryptography.
ECDH is a method for key exchange and ECDSA is used for digital signatures. ECDH and ECDSA using
256-bit prime modulus secure elliptic curves provide adequate protection for sensitive information. ECDH
and ECDSA over 384-bit prime modulus secure elliptic curves are required to protect classified information
of higher importance.
http://www.cisco.com/en/US/docs/ios-xml/ios/sec_conn_ike2vpn/configuration/15-2mt/sec-cfg-ikev2-
flex.html#GUID-6F6D8166-508A-4669-9DDC-4FE7AE9B9939
http://www.cisco.com/c/en/us/about/security-center/next-generation-cryptography.html#9