A format-preserving cipher including an encryption and a decryption scheme supporting non-linear access to input data by allowing the selection of portions of data from a potentially larger dataset to be encrypted, thus avoiding a necessarily sequential access into the input plaintext data. The cipher first defines a forward mapping from the allowable ciphertext values to an integer set of the number of such allowable ciphertext values, and a corresponding reverse mapping. It also supports exclusion of a certain set of characters from the ciphering process. Further, the encryption algorithm can encrypt the input plaintext data while preserving its original format and length and a corresponding decryption algorithm. The cipher advantageously embodies the encryption and decryption of multi-byte values or strings of data, thus fitting a variety of industrial needs.