Are Block Ciphers Pseudorandom functions? [duplicate]

Question

I am reading this page on wikipedia on Key derivation function here where it states:

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 main key, a password, or a passphrase using a pseudorandom function (which typically uses a cryptographic hash function or block cipher)

I am curious about the part that states: using a pseudorandom function (which typically uses a cryptographic hash function or block cipher)

This kind of implies that PRFs could be block cipher. Is this correct? As I assumed that PRP (pseudorandom permutations) are the ones that could be block ciphers.

Is my understanding wrong? Or the Wiki entry wrong?

Answer 1

Are Block Ciphers Pseudorandom functions?

PseudoRandom Permutations (PRP, when keyed) are synonymous with block ciphers.

This kind of implies that PRFs could be block cipher. Is this correct? block ciphers.

No, PRFs are not block ciphers. Of course, we can use them for encryption as in CTR mode.

• We can construct PRF's from hash functions.
• Hash functions can be built from PRP as in MD construction ( the one-way compression function)
• PRF can be built from PRP with Luby and Rackoff's construction.

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 main key, a password, or a passphrase using a pseudorandom function (which typically uses a cryptographic hash function or block cipher)

Or the Wiki entry wrong?

• Bcrypt is one example that uses Blowfish block cipher to derive keys from passwords.

• BPKDF2 uses SHA-1, Argon2 uses Blake2 hash function.

• HKDF uses HMAC_SHA256 and HMAC is built for PRF.

• KDF1 and KDF2 use hash functions in a simple construction ( sometimes called poor man's key derivation function)

Therefore, the entity in Wikipedia is correct.

Answer 2

Pseudo-Random Generators -> generate sequences from bits which "look" like random -> a small sequence of really random bits.

• Stream ciphers
• Block ciphers, eg in Counter Mode
• Hash function with feedback

Block cipher modes

• ECB – Electronic Code Book mode
• CBC – Cipher Block Chaining
• OFB – Output Feedback Mode (stream cipher pseudorandom generator...)
• CFB – Cipher Feedback Mode