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The salt and hash are then stored in the database. To later test if a password a user enters is correct, the same process can be performed on it (appending that user's salt to the password and calculating the resultant hash): if the result does not match the stored hash, it could not have been the correct password that was entered.
As only the salted and hashed version of a password is used in the whole login process, and the salt on the server doesn't change, a client storing passwords can store the hashed versions, and not expose the clear text password to attackers. Such hashed versions are bound to one server, which makes this useful on password reuse. [12]
The simplest example of a challenge-response protocol is password authentication, where the challenge is asking for the password and the valid response is the correct password. An adversary who can eavesdrop on a password authentication can authenticate themselves by reusing the intercepted password. One solution is to issue multiple passwords ...
A common defense against this attack is to compute the hashes using a key derivation function that adds a "salt" to each password before hashing it, with different passwords receiving different salts, which are stored in plain text along with the hash.
The PBKDF2 key derivation function has five input parameters: [9] DK = PBKDF2(PRF, Password, Salt, c, dkLen) where: PRF is a pseudorandom function of two parameters with output length hLen (e.g., a keyed HMAC)
The key setup begins with a modified form of the standard Blowfish key setup, in which both the salt and password are used to set all subkeys. There are then a number of rounds in which the standard Blowfish keying algorithm is applied, using alternatively the salt and the password as the key, each round starting with the subkey state from the ...
In cryptography, scrypt (pronounced "ess crypt" [1]) is a password-based key derivation function created by Colin Percival in March 2009, originally for the Tarsnap online backup service. [ 2 ] [ 3 ] The algorithm was specifically designed to make it costly to perform large-scale custom hardware attacks by requiring large amounts of memory.
crypt is a POSIX C library function. It is typically used to compute the hash of user account passwords. The function outputs a text string which also encodes the salt (usually the first two characters are the salt itself and the rest is the hashed result), and identifies the hash algorithm used (defaulting to the "traditional" one explained below).