XTR hệ thống khóa công khai. [175]. Đại diện rút ngắn được thực hiện bằng cách xây dựng một FP lĩnh vực như vậy mà nó có chứa một ISBN nhiều: nhóm nhỏ hơn để chính q. Chúng tôi nhận thấy rằng Nhiều chương trình mã hóa và các giao thức, | A multiple number of Phase 2 exchanges may take place after a Phase 1 exchange between the same pair of entities involved in Phase 1. Phase 2 is often referred to as Quick Mode. It relies on the shared session key agreed in Phase 1. The reason for having a multiple number of Phase 2 exchanges is that they allow the users to set up multiple connections with different security properties such as integrity-only confidentiality-only encryption with a short key or encryption with a strong key. To see a flavor of IKE let us focus our attention only on a couple of IKE Phase 1 modes. IKE Phase 1 There are eight variants for the IKE Phase 1. This is because there are three types of keys preshared symmetric key public key for encryption and public key for signature verification and in addition there are two versions of protocols based on public encryption keys one of which is intended to replace the other but the first must still be documented for backward compatibility. Thus there are actually four types of keys pre-shared symmetric key old-style public encryption key new-style public encryption key and public signature-verification key . For each key type there are two types of Phase 1 exchanges a main mode and an aggressive mode. Each main mode has six_ messages exchanges 3 messages sent frcrn an initial- I for short to a responder R for short 3 sent from R to I. A main mode is mandatory in IKE that is two users cannot run an aggressive mode with ut running a main mode first. Each aggressive mode has only three messages I initiates a message R responds one then I sends a final message to terminate a run. An aggressive mode is optional that is it can be omitted. For IKE Phase 1 we shall only describe and analyze signature based modes. Other modes generally use an encryption-then-decryption of freshness identifier mechanism for achieving authentication we have labeled such a mechanism non-standard see which we will further criticize in . .
