Runtime Configuration
The behaviour of these functions is affected by settings
in php.ini.
Table 1. Mcrypt configuration options
Name Default Changeable
mcrypt.algorithms_dir NULL PHP_INI_ALL
mcrypt.modes_dir NULL PHP_INI_ALL
For further details and definition of the PHP_INI_* constants
see ini_set().
Resource Types
This extension has no resource types defined.
Predefined Constants
The constants below are defined by this extension, and will
only be available when the extension has either been compiled
into PHP or dynamically loaded at runtime.
Mcrypt can operate in four block cipher modes (CBC, OFB,
CFB, and ECB). If linked against libmcrypt-2.4.x or higher
the functions can also operate in the block cipher mode
nOFB and in STREAM mode. Below you find a list with all
supported encryption modes together with the constants that
are defines for the encryption mode. For a more complete
reference and discussion see Applied Cryptography by Schneier
(ISBN 0-471-11709-9).
MCRYPT_MODE_ECB (electronic codebook) is suitable for random
data, such as encrypting other keys. Since data there is
short and random, the disadvantages of ECB have a favorable
negative effect.
MCRYPT_MODE_CBC (cipher block chaining) is especially suitable
for encrypting files where the security is increased over
ECB significantly.
MCRYPT_MODE_CFB (cipher feedback) is the best mode for
encrypting byte streams where single bytes must be encrypted.
MCRYPT_MODE_OFB (output feedback, in 8bit) is comparable
to CFB, but can be used in applications where error propagation
cannot be tolerated. It's insecure (because it operates
in 8bit mode) so it is not recommended to use it.
MCRYPT_MODE_NOFB (output feedback, in nbit) is comparable
to OFB, but more secure because it operates on the block
size of the algorithm.
MCRYPT_MODE_STREAM is an extra mode to include some stream
algorithms like WAKE or RC4.
Some other mode and random device constants:
MCRYPT_ENCRYPT (integer)
MCRYPT_DECRYPT (integer)
MCRYPT_DEV_RANDOM (integer)
MCRYPT_DEV_URANDOM (integer)
MCRYPT_RAND (integer)
