Block Cipher - Relation To Other Cryptographic Primitives

Relation To Other Cryptographic Primitives

Block ciphers can be used to build other cryptographic primitives, such as those below. For these other primitives to be cryptographically secure, care has to be taken to build them the right way.

• Stream ciphers can be built using block ciphers. OFB-mode and CTR mode are block modes that turn a block cipher into a stream cipher.

• Cryptographic hash functions can be built using block ciphers. See one-way compression function for descriptions of several such methods. The methods resemble the block cipher modes of operation usually used for encryption.

• Cryptographically secure pseudorandom number generators (CSPRNGs) can be built using block ciphers.

• Secure pseudorandom permutations of arbitrarily sized finite sets can be constructed with block ciphers; see Format-Preserving Encryption.

• Message authentication codes (MACs) are often built from block ciphers. CBC-MAC, OMAC and PMAC are such MACs.

• Authenticated encryption is also built from block ciphers. It means to both encrypt and MAC at the same time. That is to both provide confidentiality and authentication. CCM, EAX, GCM and OCB are such authenticated encryption modes.

Just as block ciphers can be used to build hash functions, hash functions can be used to build block ciphers. Examples of such block ciphers are SHACAL, BEAR and LION.