PHP 7.1.20 Released

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 defined 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 a block cipher mode that is generally unsuitable for most purposes. The use of this mode is not recommended.
  • MCRYPT_MODE_CBC (cipher block chaining) is a block cipher mode that is significantly more secure than ECB mode.
  • MCRYPT_MODE_CFB (cipher feedback, in 8-bit mode) is a stream cipher mode. It is recommended to use NCFB mode rather than CFB mode.
  • MCRYPT_MODE_OFB (output feedback, in 8-bit mode) is a stream cipher mode comparable to CFB, but can be used in applications where error propagation cannot be tolerated. It is recommended to use NOFB mode rather than OFB mode.
  • MCRYPT_MODE_NOFB (output feedback, in n-bit mode) is comparable to OFB mode, but operates on the full block size of the algorithm.
  • MCRYPT_MODE_STREAM is an extra mode to include some stream algorithms like "WAKE" or "RC4".

Mcrypt supports some other modes of operation for which there are no predefined constants. They can be utilised by passing a string in place of the missing constants.

  • "ctr" (counter mode) is a stream cipher mode.
  • "ncfb" (cipher feedback, in n-bit mode) is comparable to CFB mode, but operates on the full block size of the algorithm.

Some other mode and random device constants:

MCRYPT_ENCRYPT (integer)
MCRYPT_DECRYPT (integer)
MCRYPT_DEV_RANDOM (integer)
MCRYPT_DEV_URANDOM (integer)
MCRYPT_RAND (integer)

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User Contributed Notes 2 notes

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5
gordon at vixo dot com
5 years ago
These constants don't cover all the possible options.

There are two constants:
MCRYPT_MODE_OFB
MCRYPT_MODE_NOFB

These relate to using OFB mode in 8-bit feedback mode and using the same feedback length as the key

There is one constant
MCRYPT_MODE_CFB which uses 8-bit feedback mode

There ought to be a constant
MCRYPT_MODE_NCFB which uses the same feedback length as the key.

In fact you can just use the option 'ncfb' in mycrypt
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-10
Andrey Andreev
4 years ago
You can just use strings instead of the constants ... they are useless and lacking for other modes that are fully supported. Here's a list:

cbc
ecb
ofb
nofb
cfb
ncfb
ctr
stream
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