Format-Transforming Encryption (FTE) is a cryptographic primitive explored in the paper Protocol Misidentiﬁcation Made Easy with Format-Transforming Encryption . FTE allows a user to specify the format of their ouput ciphertexts using regular expressions. The libfte library implements the primitive presented in .
If you are interested in the proxy system that uses FTE to bypass DPI systems, please see fteproxy (https://github.com/kpdyer/fteproxy).
 Protocol Misidentification Made Easy with Format-Transforming Encryption, Kevin P. Dyer, Scott E. Coull, Thomas Ristenpart and Thomas Shrimpton, https://kpdyer.com/publications/ccs2013-fte.pdf