Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
MCRYPT(1)		    General Commands Manual		     MCRYPT(1)

NAME
       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  modifica-
       tion  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.

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	 algo-
       rithm,  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 re-
       dundancy	is removed). A drawback	is that	most compression programs will
       add  specific  headers in the compressed	file, thus making known	plain-
       text 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 supe-
       ruser priviledges it ensures that no important  data  (keys  etc.)  are
       written	to  disk,  as  swap etc.  Keep in mind that mcrypt was not de-
       signed 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
	      terminal,	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) en-
	      crypted 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 ap-
	      plied).

       -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 al-
	      gorithm. 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	speci-
	      fied  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.  Use-
	      full 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 encryp-
	      tion/decryption succeeds.	This is	not the	default	 in  order  to
	      use an external program to remove	sensitive data.

	--list
	      Lists all	the algorithms current supported.

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

	--list-hash
	      Lists all	the hash algorithms current 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 (\0)	and the	Newline	(\n) character
	      in the key.  A solution to this problem is to specify  the  key-
	      word 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  de-
	      fault.  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 pa-
	      rameter.

EXAMPLES
       For  mcrypt to be compatible with the solaris des(1), the following pa-
       rameters	are needed: "mcrypt -a des --keymode pkdes --bare --noiv file-
       name".

       For  mcrypt  to be compatible with the unix crypt(1), the following pa-
       rameters	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	 inse-
       cure), but note that only one key should	be used	in MCRYPT_KEY.

SEE ALSO
       crypt(1), des(1)	mcrypt(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 Mavroy-
       anopoulos (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)

NAME | SYNOPSIS | DESCRIPTION | HINTS | OPTIONS | EXAMPLES | ENVIRONMENT | SEE ALSO | DIAGNOSTICS | AUTHORS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=mcrypt&sektion=1&manpath=FreeBSD+13.0-RELEASE+and+Ports>

home | help