Here is a list of ciphers which are currently supported by the mcrypt extension. For a complete list of supported ciphers, see the defines at the end of mcrypt.h. The general rule with the mcrypt-2.2.x API is that you can access the cipher from PHP with MCRYPT_ciphername. With the libmcrypt-2.4.x and libmcrypt-2.5.x API these constants also work, but it is possible to specify the name of the cipher as a string with a call to mcrypt_module_open().
You must (in CFB and OFB mode)
or can (in CBC mode) supply an
initialization vector (IV) to the respective cipher function. The
IV must be unique and must be the same when
decrypting/encrypting. With data which is stored encrypted, you
can take the output of a function of the index under which the
data is stored (e.g. the MD5 key of the filename).
Alternatively, you can transmit the IV together with the encrypted
data (see chapter 9.3 of Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a
discussion of this topic).
Mark (2012-10-29 14:13:49)
Note, these are not the names you use in the function mcrypt_module_open to specify the algorithm.
Use mcrypt_list_algorithms to get the right names to stick in there
robin (2010-12-17 09:41:57)
The MCRYPT_TWOFISH constant when defined by mcrypt version 2.4.x and later is the 256 bit version of Twofish; it uses a 1-32 byte key, a 16 byte IV, and outputs 16 byte blocks in CBC mode.