Format-Preserving Encryption

Recommendation for Block Cipher Modes of Operation: Methods for Format-Preserving Encryption

Implemention

https://sourceforge.net/projects/format-preserving-encryption/
https://github.com/capitalone/fpe

https://en.wikipedia.org/wiki/Format-preserving_encryption
http://dx.doi.org/10.6028/NIST.SP.800-38G