Ciphers such as AES or DES are a symmetric key cipher operating on fixed-length groups of bits. They typically operate on large input data blocks i.e. 64 or more than 128, 256 bits. Some applications need smaller blocks, and possibly non-binary blocks. FNR is a flexible length small domain block cipher for encrypting objects that works without the need for padding. The encryption key length is not dependent on the input length and rather depends on underlying pseudo-random function (PRF)
Source: https://thehackernews.com/2014/06/encryption-small-domain-block-cipher.html