A format-preserving cipher including encryption and decryption schemes supporting non-linear access to input data by allowing the selection of portions of data from a potentially larger dataset to be encrypted. 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. An encryption algorithm is provided that encrypts the input plaintext data while preserving its original format and length, and a corresponding decryption algorithm is provided. The cipher advantageously embodies the encryption and decryption of multi-byte values, composite datasets, credit card numbers and discontinuous datasets, thus fitting a variety of industrial needs.