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PBKDF2 is for generating an encryption key from a password, and not necessarily for password authentication. PBKDF2 can be used for both if the number of output bits is less than or equal to the internal hashing algorithm used in PBKDF2, which is usually SHA-2 (up to 512 bits), or used as an encryption key to encrypt static data.
In one application Blowfish's slow key changing is actually a benefit: the password-hashing method (crypt $2, i.e. bcrypt) used in OpenBSD uses an algorithm derived from Blowfish that makes use of the slow key schedule; the idea is that the extra computational effort required gives protection against dictionary attacks. See key stretching.
General-purpose ciphers tend to have different design goals. In particular, AES has key and block sizes that make it nontrivial to use to generate long hash values; AES encryption becomes less efficient when the key changes each block; and related-key attacks make it potentially less secure for use in a hash function than for encryption.
Current [when?] collision-resistant hash algorithms that have provable security reductions are too inefficient to be used in practice. In comparison to classical hash functions, they tend to be relatively slow and do not always meet all of criteria traditionally expected of cryptographic hashes. Very smooth hash is an example.
SHA-3 (Secure Hash Algorithm 3) is the latest [4] member of the Secure Hash Algorithm family of standards, released by NIST on August 5, 2015. [ 5 ] [ 6 ] [ 7 ] Although part of the same series of standards, SHA-3 is internally different from the MD5 -like structure of SHA-1 and SHA-2 .
It starts off with subkeys in a standard state, then uses this state to perform a block encryption using part of the key, and uses the result of that encryption (which is more accurate at hashing) to replace some of the subkeys. Then it uses this modified state to encrypt another part of the key, and uses the result to replace more of the subkeys.
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 ...
ChaCha20-Poly1305 is an authenticated encryption with associated data (AEAD) algorithm, that combines the ChaCha20 stream cipher with the Poly1305 message authentication code. [1] It has fast software performance, and without hardware acceleration, is usually faster than AES-GCM .