Another concept of security specific to the password-based case is resistance to server compromises (see Refs.  or ). This happens in the following case: if one of the two parties is a server that has a user password function and not the password itself. Any ordinary PAKE can easily be converted into one that fits this situation, for example by simply inserting the password. (Ordinary hapss are sometimes called balanced protocols, while secure server protocols are called extended PAKes.) This detects a realistic scenario: a server can contain functions of many different users who open sessions with it to access different resources. Resistance to server compromises means that the server does not accept a user`s identity, unless it first makes a dictionary attack on the data it contains. It should be noted that this term is controversial, especially because if the server data is indeed compromised, it makes no sense to consider the associated passwords as safe, as they are trivially sensitive to offline searches. In the rest of this chapter, we will focus on balanced PAHs. Key mous that is verified by the password requires the separate implementation of a password (which may be smaller than a key) in a way that is both private and integrity. These are designed to withstand man-in-the-middle and other active attacks on the password and established keys. For example, DH-EKE, SPEKE and SRP are Diffie-Hellman password authentication variants. To avoid the use of additional off-band authentication factors, Davies and Price proposed the use of Ron Rivest and Adi Shamir`s Interlock protocol, which has come under subsequent attack and refinement. Commonly used key agreement protocols include diffie-hellman or protocols based on the RSA or ECC.
The exponential key exchange itself does not indicate prior agreement or subsequent authentication between participants. It has therefore been described as an anonymous key memorandum of understanding. DH-CHAP is an Internet standard soon available for authenticating devices that connect to a fiber chain switch. DH-CHAP is a secure authentication protocol for key exchange, which supports both switch-to-switch authentication and host-to-switch authentication. DH-CHAP supports algorithm-based MD-5 and SHA-1 authentication. The key agreement refers to a key exchange form (see also key key) in which two or more users execute a protocol in order to safely release a resulting key value. An important transport protocol can be used as an alternative to the key agreement. The distinguishing feature of a key MOU is that participating users contribute equally to the calculation of the resulting common key value (unlike a user who calculates and distributes a key value to other users). A naïve example of a key exchange protocol is that a party writes a secret key, puts it in an unman manipulated envelope and sends it to the recipient. If the envelope is intact, the secret key can be used by both parties to decrypt the messages.
In the classic key exchange, the exhaustive search for the right long-term key simply cannot be made possible by construction: it is totally random and very long. On the other hand, a password is probably short and is created from a small set of values with a coincidence less than the ideal, which allows an exhaustive search. We illustrate the impact of this phenomenon with a “stupid” protocol. This type of attack is probably the most important to avoid in the design of the PAKE, because an attacker does not need to be online to execute it. Offline attackers have more time and computing power for the simple reason that they cannot be interrupted. In the example above, it was only necessary for the opponent to record an exchange. From there, there is no way to disrupt the opponent`s behavior. We call these attacks offline dictionary attacks. To prevent them, it is necessary that the protocol