Patent ID: 8855296

Claim:
A method for encrypting a data string to produce a corresponding encrypted data string using a format-preserving block cipher on a data processing system, comprising: wherein the data string contains characters and has a format specifying a legal set of character values for each of the characters of the data string, wherein the data string contains a first string of characters that has a first format specifying a legal set of character values for each of the characters of the first string and contains a second string of characters that has a second format specifying a legal set of character values of each of the characters of the second string; with a format-preserving combining operation, combining a first subkey with the first string of characters while preserving the first format of the first string of characters; and with the format-preserving combining operation, combining a second subkey with the second string of characters while preserving the second format of the second string of characters.