A portable C implementation of ipcrypt, a 32-bit block cipher that can be used to "anonymize" IP addresses in log files.
The cipher was designed by Jean-Philippe Aumasson.
Reference implementation in Python: ipcrypt.
Usage:
encrypt [key]
Encrypts all ip adresses found in stdin with [key]. If no key is provided a random 16 character key is used.
decrypt key
Decrypts all ip adresses found in stdin using key