VAES3 scheme for FFX

VAES stands for variable AES. VAES3 is the third generation format-preserving encryption algorithm that was developed in a report [4] simultaneously with the comprehensive paper on FPE [1] and subsequently updated slightly to be in concert with the FFX standard proposal. The standard proposal of FFX includes, in an appendix, example instantiations called A2 and A10. A follow on addendum [3] includes an instantiation called FFX[radix] . The stated intent of FFX is that it is a framework under which many implementations are compliant. The VAES3 scheme is compliant to those requirements. VAES3 was designed to meet security goals and requirements beyond the original example instantiations, and its design goals are slightly different than those of FFX[radix]. One of the unique features of VAES3 is a subkey step that enhances security and lengthens the lifetime of the key.