In the first quick mode packet, the initiator sends the identity information, IPSec SA proposal, Nonce payload, and the optional Key Exchange (KE) payload in case Perfect Forward Secrecy (PFS) is used

Perfect Forward Secrecy (PFS) is a cryptographic technique where the newly generated keys are unrelated to any previously generated key. With PFS enabled, the security Cisco ASA generates a new set of keys which is used during the IPSec Phase 2 negotiations. Without PFS, the Cisco ASA uses Phase 1 keys during the Phase 2 negotiations. The Cisco ASA uses Diffie-Hellman group 1, 2, 5, and 7 for PFS to generate the keys. Diffie-Hellman group 1 uses 768-bits modulus size to generate the keys, while group 2 uses 1024-bits and group 5 uses a 1536 bits modulus size. Group 7, where the elliptical curve field size is 163 bits, is designed for the faster computation of keys usually used by the handheld PCs. Group 5 is the most secure technique but requires more processing overhead. The syntax to configure PFS is

crypto map map-name seq-num set pfs {group1 | group2 | group5 | group7}

it is Optional Command

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