CryptologyII.3 Modes of Operation of Block Ciphers |
|
The complete Section II.3 as an PDF file.
A bitblock encryption function f : F2n → F2n is primarily defined on blocks of fixed length n. To encrypt longer (or shorter) bit sequences the sender must
Then each block is encrypted by f, but in general one uses some sort of »chaining«. Four chaining procedures, called »modes of operation« were standardized together with DES:
The official web site for these standards is
https://csrc.nist.gov/projects/block-cipher-techniques
For a description of the modes a suitable general framework is a »block alphabet« Σ, with F2n as most important example, equipped with a group composition *.
Furthermore we fix an encryption function
f : Σ → Σ.
The dependence on the key doesn't matter in this context and therefore is dropped in the notation.