BS ISO/IEC 10116:2015 pdf download-Information technology — Security techniques — Modes of operation for an n-bit block cipher.
5 Requirements For all of the described modes, a block cipher has to be selected (see ISO/IEC 1 8033-3 and ISO/IEC 291 92-2). For the Electronic Codebook (ECB) mode there are no additional parameter values that need to be selected. For the Cipher Block Chaining (CBC) mode of operation (see clause 7), one parameter m needs to be selected. For the Cipher Feedback (CFB) mode of operation (see clause 8), three parameters r, j and k need to be selected. For the Output Feedback (OFB) mode of operation (see clause 9) and the Counter (CTR) mode of operation (see clause 1 0), one parameter j needs to be selected. When one of these modes of operation is used the same parameter value(s) need to be chosen and used by all communicating parties. These parameters need not be kept secret. All modes of operation specified in this International Standard require the parties encrypting and decrypting a data string to share a secret key K for the block cipher in use. All modes of operation apart from the electronic Codebook (ECB) mode also require the parties to share a starting variable SV, where the length of SV will depend on the mode in use. The value of the starting variable should normally be different for every data string encrypted using a particular key (see also Annex B). How keys and starting variables are managed and distributed is outside the scope of this International Standard. The encrypter and all potential decrypters must agree on a padding method, unless messages to be encrypted are always a multiple of m bits (m = n for ECB and CBC modes, m = j for CFB, OFB and CTR modes) in length or unless the mode does not require padding. Such a padding method must take a (non-empty) bit string P of arbitrary length as input, and give a sequence of m-bit plaintext blocks as output.