Crypt::HCE_SHA is a Perl extension implementing one way hash chaining encryption using SHA.
$hce_sha = Crypt::HCE_SHA->new("SharedSecret", "Random01,39j309ad");
$crypted = $hce_sha->hce_block_encrypt("Encrypt this information");
$info = $hce_sha->hce_block_decrypt($crypted);
$mime_crypted = $hce_sha->hce_block_encode_mime("Encrypt and Base64 this information");
$info = $hce_sha->hce_block_decode_mime($mime_crypted);
This module implements a chaining block cipher using a one way hash. This method of encryption is the same that is used by radius (RFC2138) and is also described in Applied Cryptography.
Two interfaces are provided in the module. The first is straight block encryption/decryption the second does base64 mime encoding/decoding of the encrypted/decrypted blocks.
The idea is the the two sides have a shared secret that supplies one of the keys and a randomly generated block of bytes provides the second key. The random key is passed in cleartext between the two sides.
An example client and server are packaged as modules with this module. They are used in the tests. They can be found in the examples directory.
Thanks to Jake Angerman for the bug report on the bug in key generation for the chaining portion of the algorithm.