MCRYPT(1)                                                     General Commands Manual                                                    MCRYPT(1)

NAME

       crypt, mcrypt, mdecrypt - encrypt or decrypt files

SYNOPSIS

       mcrypt [ -dLFubhvrzp ] [-a algorithm] [-c config_file] [-m mode] [-s keysize] [-o keymode] [-k key1 key2 ...]  [-f keyfile] [ filename ...  ]

       mdecrypt [ -LFusbhvzp ] [-a algorithm] [-c config_file] [-m mode] [-s keysize] [-o keymode] [-k key1 key2 ...]  [-f keyfile] [ filename ...
       ]

DESCRIPTION

       Mcrypt is a simple crypting program, a replacement for the old unix crypt(1).  When encrypting or decrypting a file, a new file is  created
       with the extension .nc and mode 0600. The new file keeps the modification date of the original.  The original file may be deleted by speci-
       fying the -u parameter.  If no files are specified, the standard input is encrypted to the standard output.

       Mcrypt uses all the symmetric algorithms included in libmcrypt.

       crypt is a small shell wrapper around mcrypt to emulate the old unix crypt command.  For more information run crypt --help !

HINTS

       By default, mcrypt , when one of these algorithms is specified, prompts something like:
        Enter passphrase: ...
        You should then enter a passphrase long enough (512 characters is the maximum length). Now in order to encrypt the file, The passphrase is
       transformed  using  the specified (or the default) key generation algorithm, and a random salt. The produced value is then used as the key,
       which is fed to the algorithm.

       Algorithm Vulnerability: Most algorithms today are designed to resist in specific attacks.  None of them is proved not to be vulnerable  to
       some kind of attack not as yet known.

       Compression:  By  compressing your data before encryption you gain both in efficiency (faster encryption) and safety of your data (language
       redundancy is removed). A drawback is that most compression programs will add specific headers in the compressed file,  thus  making  known
       plaintext attacks easier.  Compression after encryption is useless and may result to compressed files with longer size than the original.

       Error  Recovery:  There  is some error recovery in mcrypt.  If bytes are removed or lost from the file or stream in ECB, CBC and OFB modes,
       are impossible to recover, although CFB mode will recover. If some bytes are altered then a full block of  plaintext  is  affected  in  ECB
       mode,  two  blocks  in CBC and CFB modes, but only the corresponding byte in OFB mode.  Mcrypt uses a 32 bit CRC to check for errors in the
       encrypted files.

       Extra security: For the very paranoid, if mcrypt is executed with superuser priviledges it ensures that no important data (keys  etc.)  are
       written to disk, as swap etc.  Keep in mind that mcrypt was not designed to be a setuid program, so you shouldn't make it one.

       Do not rely on the fact that an algorithm has a large key size, try to use long passphrases and try to make them unpredictable.

       All the block algorithms above support these modes of encryption:

       ECB: The Electronic CodeBook mode. It is the simplest mode to use with a block cipher. Encrypts each block independently.

       CBC:  The  Cipher  Block Chaining mode. It is better than ECB since the plaintext is XOR'ed with the previous ciphertext. A random block is
       placed as the first block so the same block or messages always encrypt to something different. (This is the default mode)

       CFB: The Cipher-Feedback Mode (in 8bit). This is a self-synchronizing stream cipher implemented from a block cipher.

       OFB: The Output-Feedback Mode (in 8bit). This is a synchronous stream cipher implemented from a block cipher. It is  intended  for  use  in
       noisy  lines,  because  corrupted  ciphertext  blocks  do not corrupt the plaintext blocks that follow. Insecure when used to encrypt large
       amounts of data, so I recommend against using it.

       nOFB: The Output-Feedback Mode (in nbit). n Is the size of the block of the algorithm. This is a synchronous stream cipher implemented from
       a block cipher. It is intended for use in noisy lines, because corrupted ciphertext blocks do not corrupt the plaintext blocks that follow.

       Encrypted files can be restored to their original form using mcrypt -d or mdecrypt

       mdecrypt  takes  a list of files on its command line and creates a new file for each file whose name ends with .nc by removing the ".nc" or
       by adding ".dc" to the end of the file name if .nc is not in the encrypted file's name.

OPTIONS

       -F --force
              Force output on standard output or input from stdin if that is a terminal.  By default mcrypt will not output encrypted data to ter-
              minal, nor read encrypted data from it.

       -z --gzip
              Use  gzip  (if  it  exists  in your system) to compress files before encryption.  If specified at decryption time it will decompress
              these files.

       -p --bzip2
              Use bzip2 (if it exists in your system) to compress files before encryption.  If specified at decryption  time  it  will  decompress
              these files.

        --openpgp-z INT
              This option will enable compression in OpenPGP (RFC2440) encrypted files.

       -d --decrypt
              Decrypt.

        --help
              Display a help screen and quit.

       -v --version
              Version. Display the version number and quit.

       -L --license
              Display the mcrypt's license and quit.

       -o --keymode MODE
              MODE  may be one of the keymodes listed by the --list-keymodes parameter.  It actually is the convertion to the key before it is fed
              to the algorithm.  It is recommended to leave it as is, if you do not know what it is.  However  if  you  still  want  to  use  this
              option, you might want to use the 'hex' mode which allows you to specify the key in hex (and no convertion will by applied).

       -h --hash HASH_ALGORITHM
              HASH_ALGORITHM  may  be  one of the algorithms listed by the --list-hash parameter.  This is the digest that will be appended to the
              file to be encrypted, in order to detect file corruption. The default is the CRC32 checksum.

       -s --keysize SIZE
              SIZE is the algorithm's key size in bytes (not the size of the passphrase). It defaults to the maximum key supported  by  the  algo-
              rithm. The maximum key sizes of the algorithms may be obtained by the --list parameter. It is safe not to touch this.

       -g --openpgp
              This  option will make mcrypt to use the OpenPGP (RFC2440) file format for encrypted files. This will make files encrypted by mcrypt
              accessible from any OpenPGP compliant application.

       -b --bare
              No important information like the algorithm, mode, the bit mode and the crc32 of the original file  are  written  in  the  encrypted
              file.   The  security  lies  on  the  algorithm  not  on obscurity so this is NOT the default. This flag must also be specified when
              decrypting a bare encrypted file.  When the bare flag is specified decryption and encryption are faster. This may  be  usefull  when
              using mcrypt to encrypt a link or something like that.

       --flush
              Flushes the output (ciphertext or plaintext) immediately. Usefull if mcrypt is used with pipes.

       --time Prints some timing information (encryption speed etc.)

       --nodelete
              When  this  option  is  specified  mcrypt does not delete the output file, even if decryption failed. This is usefull if you want to
              decrypt a corrupted file.

       -q --quiet
              Suppress some not critical warnings.

       -u --unlink
              Unlink (delete) the input file if the whole process of encryption/decryption succeeds. This is not the default in order  to  use  an
              external program to remove sensitive data.

        --list
              Lists all the algorithms currently supported.

        --list-keymodes
              Lists all the key modes currently supported.

        --list-hash
              Lists all the hash algorithms currently supported.

       -r --random
              Use  /dev/(s)random instead of /dev/urandom. This may need some key input or mouse move to proceed.  If your system does not support
              /dev/random or /dev/urandom, a random gatherer will be used.

       -k --key KEY1 KEY2 ...
              Enter the keyword(s) via the command line. The KEY(s) is/are then used as keyword instead of prompting for them. Keep in  mind  that
              someone may see the command you are executing and so your keyword(s).

       -c --config FILE
              Use  the  specified configuration file. The default is .mcryptrc in your home directory. The format of the configuration file is the
              same as the parameters. An example file is:
               algorithm safer+
               mode cbc
               key a_very_secret_one

       -f --keyfile FILE
              Enter the keyword(s) via a file. One keyword is read per line.  The first keyword read is used for the first file,  the  second  for
              the  second  file etc. If the keywords are less than the files then the last keyword is used for the remaining. A limitation is that
              you cannot use the NULL () and the Newline (
) character in the key.  A solution to this problem is to specify the keyword in hex
              mode.

       -m --mode MODE
              Mode  of  encryption  and  decryption. These modes are currently supported: ECB, CFB, OFB, nOFB, CBC and STREAM. CBC is the default.
              Unless the bare flag is specified there is no need to specify these modes for decryption.  For stream algorithms  (like  WAKE)  mode
              should be STREAM.

       -a --algorithm ALGORITHM
              The algorithm used to encrypt and decrypt. Unless the bare flag is specified there is no need to specify these for decryption.

              The algorithms currently supported are shown with the --list parameter.

EXAMPLES

       For  mcrypt  to  be  compatible  with the solaris des(1), the following parameters are needed: "mcrypt -a des --keymode pkdes --bare --noiv
       filename".

       For mcrypt to be compatible with the unix crypt(1), the following parameters are needed: "mcrypt -a enigma --keymode  scrypt  --bare  file-
       name".

       To encrypt a file using a stream algorithm (eg. Arcfour), the following parameters are needed: "mcrypt -a arcfour --mode stream filename".

ENVIRONMENT

       Mcrypt uses the following environment variables:

       MCRYPT_KEY: to specify the key

       MCRYPT_ALGO: to specify the algorithm

       MCRYPT_MODE: to specify the algorithm's mode

       MCRYPT_KEY_MODE: to specify the key mode

       You can use these instead of using the command line (which is insecure), but note that only one key should be used in MCRYPT_KEY.

SEE ALSO

       des_crypt(3)

DIAGNOSTICS

       Exit status is normally 0; if an error occurs, exit status is something other than 0.

       Usage: mcrypt [-dLFubhvrzp] [-f keyfile] [-k key1 key2 ...] [-m mode] [-o keymode] [-a algorithm] [-c config_file] [filename ...]

AUTHORS

       Version 2.6.0 Copyright (C) 1998,1999,2000,2001,2002 Nikos Mavroyanopoulos (nmav@gnutls.org).

       Thanks to all the people who reported problems and suggested various improvements for mcrypt; who are too numerous to cite here.

local                                                               03 May 2003                                                          MCRYPT(1)