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When someone requests access, the password they submit is hashed and compared with the stored value. If the database is stolen (an all-too-frequent occurrence [28]), the thief will only have the hash values, not the passwords. Passwords may still be retrieved by an attacker from the hashes, because most people choose passwords in predictable ways.
Example of a Key Derivation Function chain as used in the Signal Protocol.The output of one KDF function is the input to the next KDF function in the chain. In cryptography, a key derivation function (KDF) is a cryptographic algorithm that derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudorandom function (which typically uses a ...
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.
A universal hashing scheme is a randomized algorithm that selects a hash function h among a family of such functions, in such a way that the probability of a collision of any two distinct keys is 1/m, where m is the number of distinct hash values desired—independently of the two keys. Universal hashing ensures (in a probabilistic sense) that ...
In 2013, the Password Hashing Competition (PHC) was held to develop a more resistant approach. On 20 July 2015 Argon2 was selected as the final PHC winner, with special recognition given to four other password hashing schemes: Catena, Lyra2, yescrypt and Makwa. [14] Another alternative is Balloon hashing, which is recommended in NIST password ...
For example, bcrypt cannot be used to derive a 512-bit key from a password. At the same time, algorithms like pbkdf2, scrypt, and argon2 are password-based key derivation functions - where the output is then used for the purpose of password hashing rather than just key derivation. Password hashing generally needs to complete < 1000 ms.
A common example is the use of hashes to store password validation data. Rather than store the plaintext of user passwords, an access control system typically stores a hash of the password. When a person requests access, the password they submit is hashed and compared with the stored value.
The pass the hash technique was originally published by Paul Ashton in 1997 [6] and consisted of a modified Samba SMB client that accepted user password hashes instead of cleartext passwords. Later versions of Samba and other third-party implementations of the SMB and NTLM protocols also included the functionality.