Some were proven faulty, and some were considered for further investigation. During these workshops a few other modes were proposed. To help with the analysis of AES, two NIST workshops were dedicated to the study of various block cipher modes (see ). We do not attempt to be thorough in our description, as there are various materials (which will be mentioned throughout) devoted to this subject. In addition, there are some modes that are not yet standardized, like the GMC mode proposed by McGrew and Viega. 81), and CTR mode (specified in SP 800-38A). The modes in SP 800-38A are updated versions of the ECB, CBC, CFB, OFB modes (all specified in FIPS Pub.

In NIST’s Special Publication 800-38A, five confidentiality modes are specified for use with any approved block cipher, like the AES algorithm. There are four modes more often used (ECB, CBC, OFB, CFB). Cusick, Pantelimon Stănică, in Cryptographic Boolean Functions and Applications, 2009 7.3 Block Ciphers’ Modes of Operation 7.3.1 Confidentiality modesĪny block cipher can be operated in several modes. As a reflection of the advance in computer speeds, the minimum acceptable key length for AES was chosen to be 128 bits. This led to the approval of AES as the new government standard in 2002. Variants of DES with a longer key length can be employed, but the government decided to seek a completely new cipher via public competition. The original key size for DES was 56 bits, but by 2000 this had become too small to give security against a simple keyspace search attack. The first such block cipher to achieve widespread use was DES, which became the government approved standard for electronic banking applications in the mid 1970s. Most modern block ciphers are made up of a fixed number of rounds, where each round involves applying a sequence of operations to a block of plaintext that has been modified in the preceding rounds. The cipher maps an n bit plaintext to an n bit ciphertext, using a secret key of some fixed size the mapping function must be invertible, so decryption is accomplished by simply applying the inverse map to the ciphertext. Cusick Professor of Mathematics, Pantelimon Stanica Professor of Mathematics, in Cryptographic Boolean Functions and Applications (Second Edition), 2017 AbstractĪ block cipher typically operates on a plaintext which is broken into separate blocks of fixed length.

Block cipher