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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 ...
These examples assume that a consumer CPU can do about 65,000 SHA-1 hashes in one second. Thus, a program that uses key stretching can use 65,000 rounds of hashes and delay the user for at most one second. Testing a trial password or passphrase typically requires one hash operation.
PBKDF2 applies a pseudorandom function, such as hash-based message authentication code (HMAC), to the input password or passphrase along with a salt value and repeats the process many times to produce a derived key, which can then be used as a cryptographic key in subsequent operations.
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.
More generally, k-independent hashing functions provide a secure message authentication code as long as the key is used less than k times for k-ways independent hashing functions. Message authentication codes and data origin authentication have been also discussed in the framework of quantum cryptography.
Source: [4] Function Argon2 Inputs: password (P): Bytes (0..2 32-1) Password (or message) to be hashed salt (S): Bytes (8..2 32-1) Salt (16 bytes recommended for password hashing) parallelism (p): Number (1..2 24-1) Degree of parallelism (i.e. number of threads) tagLength (T): Number (4..2 32-1) Desired number of returned bytes memorySizeKB (m): Number (8p..2 32-1) Amount of memory (in ...
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.
The Whirlpool hash function is a Merkle–Damgård construction based on an AES-like block cipher W in Miyaguchi–Preneel mode. [2] The block cipher W consists of an 8×8 state matrix of bytes, for a total of 512 bits. The encryption process consists of updating the state with four round functions over 10 rounds.