Symmetric-key algorithm

Symmetric-key algorithms are a chic of algorithms for cryptography that use trivially related, generally identical, cryptographic keys for both encryption of plaintext and decryption of ciphertext. The encryption key is trivially accompanying to the decryption key, in that they may be identical or there is a simple transformation to go amid the two keys. The keys, in practice, represent a aggregate abstruse amid two or added parties that can be acclimated to advance a clandestine advice link. Other agreement for symmetric-key encryption are secret-key, single-key, shared-key, one-key, and private-key encryption. Use of the aftermost and aboriginal agreement can actualize ambiguity with agnate analogue acclimated in public-key cryptography. Symmetric-key cryptography is to be assorted with asymmetric-key cryptography.

Types of symmetric-key algorithms

Symmetric-key encryption can use either beck ciphers or block ciphers

.

Stream ciphers encrypt the $.25 of a bulletin one at a time

.

Block ciphers booty a cardinal of $.25 and encrypt them as a distinct unit. Blocks of 64 $.25 accept been frequently used. The Advanced Encryption Standard (AES) algorithm accustomed by NIST in December 2001 uses 128-bit blocks.

Cryptographic primitives based on symmetric ciphers

Symmetric ciphers are generally acclimated

to accomplish added cryptographic primitives than aloof encryption

.

Encrypting a bulletin does not agreement that this bulletin is not afflicted while encrypted. Hence generally a bulletin affidavit cipher is added to a ciphertext to ensure that changes to the ciphertext will be acclaimed by the receiver. Bulletin affidavit codes can be complete from symmetric ciphers (e.g. CBC-MAC

).

However, symmetric ciphers additionally can be

acclimated for non-repudiation purposes by ISO 13888-2 standard.

Another appliance is to body assortment functions from block ciphers. See one-way compression action for descriptions of several such methods.

Construction of symmetric ciphers

Many avant-garde block ciphers are based on a architecture proposed by Horst Feistel. Feistel's architecture makes it accessible to body invertible functions from added functions that are themselves not invertible.

Security of symmetric ciphers

Symmetric ciphers accept historically been affected to known-plaintext attacks, called plaintext attacks, cogwheel cryptanalysis and beeline cryptanalysis. Careful architecture of the functions for anniversary annular can abundantly abate the affairs of a acknowledged attack.

Key generation

When acclimated with agee ciphers for key transfer, pseudorandom key generators are about consistently acclimated to accomplish the symmetric blank affair keys. However, abridgement of randomness in those generators or in their initialization vectors is adverse and has led to cryptanalytic break in the past. Therefore, it is capital that an accomplishing uses a antecedent of aerial anarchy for its initialization.