Пакет: libxcrypt-devel

CRYPT(5)		    BSD File Formats Manual		      CRYPT(5)

NAME
     crypt — storage format for hashed passphrases and available hashing meth‐
     ods

DESCRIPTION
     The hashing methods implemented by crypt(3) are designed only to process
     user passphrases for storage and authentication; they are not suitable
     for use as general-purpose cryptographic hashes.

     Passphrase hashing is not a replacement for strong passphrases.  It is
     always possible for an attacker with access to the hashed passphrases to
     guess and check possible cleartext passphrases.  However, with a strong
     hashing method, guessing will be too slow for the attacker to discover a
     strong passphrase.

     Most of the hashing methods use a “salt” to perturb the hash function, so
     that the same passphrase may produce many possible hashes.	 Newer methods
     accept longer salt strings.  The salt should be chosen at random for each
     user.  Salt defeats a number of attacks:

     1.	  It is not possible to hash a passphrase once and then test it
	  against each account's stored hash; the hash calculation must be re‐
	  peated for each account.

     2.	  It is not possible to tell whether two accounts use the same
	  passphrase without successfully guessing one of the phrases.

     3.	  Tables of precalculated hashes of commonly used passphrases must
	  have an entry for each possible salt, which makes them impractically
	  large.

     Most of the hashing methods are also deliberately engineered to be slow;
     they use many iterations of an underlying cryptographic primitive to in‐
     crease the cost of each guess.  The newer hashing methods allow the num‐
     ber of iterations to be adjusted, using the “processing cost” parameter
     to crypt_gensalt(3).  For memory-hard hashing methods such as yescrypt,
     this parameter also adjusts the amount of memory needed to compute a
     hash.  Having this configurable makes it possible to keep password guess‐
     ing attacks against the hashes slow and costly as hardware improves.

FORMAT OF HASHED PASSPHRASES
     All of the hashing methods supported by crypt(3) produce a hashed
     passphrase which consists of four components: prefix, options, salt, and
     hash.  The prefix controls which hashing method is to be used, and is the
     appropriate string to pass to crypt_gensalt(3) to select that method.
     The contents of options, salt, and hash are up to the method.  Depending
     on the method, the prefix and options components may be empty.

     The setting argument to crypt(3) must begin with the first three compo‐
     nents of a valid hashed passphrase, but anything after that is ignored.
     This makes authentication simple: hash the input passphrase using the
     stored hashed passphrase as the setting, and then compare the result to
     the stored hashed passphrase.

     Hashed passphrases are always entirely printable ASCII, and do not con‐
     tain any whitespace or the characters ‘:’, ‘;’, ‘*’, ‘!’, or ‘\’.	(These
     characters are used as delimiters and special markers in the passwd(5)
     and shadow(5) files.)

     The syntax of each component of a hashed passphrase is up to the hashing
     method.  ‘$’ characters usually delimit components, and the salt and hash
     are usually encoded as numerals in base 64.  The details of this base-64
     encoding vary among hashing methods.  The common “base64” encoding speci‐
     fied by RFC 4648 is usually not used.

AVAILABLE HASHING METHODS
     This is a list of all the hashing methods supported by crypt(3), roughly
     in decreasing order of strength.  Many of the older methods are now con‐
     sidered too weak to use for new passphrases.  The hashed passphrase for‐
     mat is expressed with extended regular expressions (see regex(7)) and
     does not show the division into prefix, options, salt, and hash.

   yescrypt
     yescrypt is a scalable passphrase hashing scheme designed by Solar De‐
     signer, which is based on Colin Percival's scrypt.	 While yescrypt's
     strength against password guessing attacks comes from its algorithm de‐
     sign, its cryptographic security is guaranteed by its use of SHA-256 on
     the outer layer.  The SHA-256 hash function has been published by NIST in
     FIPS PUB 180-2 (and its subsequent revisions such as FIPS PUB 180-4) and
     by the IETF as RFC 4634 (and subsequently RFC 6234).  Recommended for new
     hashes.

     Prefix
	 "$y$"

     Hashed passphrase format
	 \$y\$[./A-Za-z0-9]+\$[./A-Za-z0-9]{,86}\$[./A-Za-z0-9]{43}

     Maximum passphrase length
	 unlimited

     Hash size
	 256 bits

     Salt size
	 up to 512 (128+ recommended) bits

     Processing cost parameter
	 1 to 11 (logarithmic, also affects memory usage)

   gost-yescrypt
     gost-yescrypt uses the output from yescrypt as an input message to HMAC
     with the GOST R 34.11-2012 (Streebog) hash function with a 256-bit di‐
     gest.  Thus, yescrypt's cryptographic properties are superseded by those
     of the GOST hash function.	 This hashing method is useful in applications
     that need modern passphrase hashing, but have to rely on GOST algorithms.
     The GOST R 34.11-2012 (Streebog) hash function has been published by the
     IETF as RFC 6986.	Acceptable for new hashes where required.

     Prefix
	 "$gy$"

     Hashed passphrase format
	 \$gy\$[./A-Za-z0-9]+\$[./A-Za-z0-9]{,86}\$[./A-Za-z0-9]{43}

     Maximum passphrase length
	 unlimited

     Hash size
	 256 bits

     Salt size
	 up to 512 (128+ recommended) bits

     Processing cost parameter
	 1 to 11 (logarithmic, also affects memory usage)

   scrypt
     scrypt is a password-based key derivation function created by Colin Per‐
     cival, originally for the Tarsnap online backup service.  The algorithm
     was specifically designed to make it costly to perform large-scale custom
     hardware attacks by requiring large amounts of memory.  In 2016, the
     scrypt algorithm was published by IETF as RFC 7914.

     Prefix
	 "$7$"

     Hashed passphrase format
	 \$7\$[./A-Za-z0-9]{11,97}\$[./A-Za-z0-9]{43}

     Maximum passphrase length
	 unlimited

     Hash size
	 256 bits

     Salt size
	 up to 512 (128+ recommended) bits

     Processing cost parameter
	 6 to 11 (logarithmic, also affects memory usage)

   bcrypt
     A hash based on the Blowfish block cipher, modified to have an extra-ex‐
     pensive key schedule.  Originally developed by Niels Provos and David
     Mazieres for OpenBSD and also supported on recent versions of FreeBSD and
     NetBSD, on Solaris 10 and newer, and on several GNU/*/Linux distribu‐
     tions.

     Prefix
	 "$2b$"

     Hashed passphrase format
	 \$2[abxy]\$[0-9]{2}\$[./A-Za-z0-9]{53}

     Maximum passphrase length
	 72 characters

     Hash size
	 184 bits

     Salt size
	 128 bits

     Processing cost parameter
	 4 to 31 (logarithmic)

     The alternative prefix "$2y$" is equivalent to "$2b$".  It exists for
     historical reasons only.  The alternative prefixes "$2a$" and "$2x$" pro‐
     vide bug-compatibility with crypt_blowfish 1.0.4 and earlier, which in‐
     correctly processed characters with the 8th bit set.

   sha512crypt
     A hash based on SHA-2 with 512-bit output, originally developed by Ulrich
     Drepper for GNU libc.  Supported on Linux but not common elsewhere.  Ac‐
     ceptable for new hashes.  The default processing cost parameter is 5000,
     which is too low for modern hardware.

     Prefix
	 "$6$"

     Hashed passphrase format
	 \$6\$(rounds=[1-9][0-9]+\$)?[^$:\n]{1,16}\$[./0-9A-Za-z]{86}

     Maximum passphrase length
	 unlimited

     Hash size
	 512 bits

     Salt size
	 6 to 96 bits

     Processing cost parameter
	 1000 to 999,999,999

   sha256crypt
     A hash based on SHA-2 with 256-bit output, originally developed by Ulrich
     Drepper for GNU libc.  Supported on Linux but not common elsewhere.  Ac‐
     ceptable for new hashes.  The default processing cost parameter is 5000,
     which is too low for modern hardware.

     Prefix
	 "$5$"

     Hashed passphrase format
	 \$5\$(rounds=[1-9][0-9]+\$)?[^$:\n]{1,16}\$[./0-9A-Za-z]{43}

     Maximum passphrase length
	 unlimited

     Hash size
	 256 bits

     Salt size
	 6 to 96 bits

     Processing cost parameter
	 1000 to 999,999,999

   sha1crypt
     A hash based on HMAC-SHA1.	 Originally developed by Simon Gerraty for
     NetBSD.  Not as weak as the DES-based hashes below, but SHA-1 is so cheap
     on modern hardware that it should not be used for new hashes.

     Prefix
	 "$sha1"

     Hashed passphrase format
	 \$sha1\$[1-9][0-9]+\$[./0-9A-Za-z]{1,64}\$[./0-9A-Za-z]{8,64}[./0-9A-
	 Za-z]{32}

     Maximum passphrase length
	 unlimited

     Hash size
	 160 bits

     Salt size
	 6 to 384 bits

     Processing cost parameter
	 4 to 4,294,967,295

   SunMD5
     A hash based on the MD5 algorithm, originally developed by Alec David
     Muffett for Solaris.  Not adopted elsewhere, to our knowledge.  Not as
     weak as the DES-based hashes below, but MD5 is so cheap on modern hard‐
     ware that it should not be used for new hashes.

     Prefix
	 "$md5"

     Hashed passphrase format
	 \$md5(,rounds=[1-9][0-9]+)?\$[./0-9A-Za-z]{8}\${1,2}[./0-9A-Za-z]{22}


     Maximum passphrase length
	 unlimited

     Hash size
	 128 bits

     Salt size
	 48 bits

     Processing cost parameter
	 4096 to 4,294,963,199

   md5crypt
     A hash based on the MD5 algorithm, originally developed by Poul-Henning
     Kamp for FreeBSD.	Supported on most free Unixes and newer versions of
     Solaris.  Not as weak as the DES-based hashes below, but MD5 is so cheap
     on modern hardware that it should not be used for new hashes.  Processing
     cost is not adjustable.

     Prefix
	 "$1$"

     Hashed passphrase format
	 \$1\$[^$:\n]{1,8}\$[./0-9A-Za-z]{22}

     Maximum passphrase length
	 unlimited

     Hash size
	 128 bits

     Salt size
	 6 to 48 bits

     Processing cost parameter
	 1000

   bsdicrypt (BSDI extended DES)
     An extension of traditional DES, which eliminates the length limit, in‐
     creases the salt size, and makes the time cost tunable.  It originates
     with BSDI BSD/OS and is also available on at least NetBSD, OpenBSD, and
     FreeBSD due to the use of David Burren's FreeSec library.	It is much
     better than traditional DES and bigcrypt, but still should not be used
     for new hashes.

     Prefix
	 "_"

     Hashed passphrase format
	 _[./0-9A-Za-z]{19}

     Maximum passphrase length
	 unlimited (ignores 8th bit)

     Hash size
	 64 bits

     Effective key size
	 up to 56 bits

     Salt size
	 24 bits

     Processing cost parameter
	 1 to 16,777,215 (must be odd)

   descrypt (Traditional DES)
     The original hashing method from Unix V7, based on the DES block cipher.
     Because DES is cheap on modern hardware, because there are only 4096 pos‐
     sible salts and 2**56 distinct passphrases, which it truncates to 8 char‐
     acters, it is feasible to discover any passphrase hashed with this
     method.  It should only be used if you absolutely have to generate hashes
     that will work on an old operating system that supports nothing else.

     Prefix
	 "" (empty string)

     Hashed passphrase format
	 [./0-9A-Za-z]{13}

     Maximum passphrase length
	 8 characters (ignores 8th bit)

     Hash size
	 64 bits

     Effective key size
	 up to 56 bits

     Salt size
	 12 bits

     Processing cost parameter
	 25

   bigcrypt
     A weak extension of traditional DES, available on some commercial Unixes.
     All it does is raise the length limit from 8 to 128 characters, and it
     does this in a crude way that allows attackers to guess chunks of a long
     passphrase separately and in parallel, which may make guessing even eas‐
     ier than for traditional DES above.  It should not be used for new
     hashes.

     Prefix
	 "" (empty string)

     Hashed passphrase format
	 [./0-9A-Za-z]{13,178}

     Maximum passphrase length
	 128 characters (ignores 8th bit)

     Hash size
	 up to 1024 bits

     Effective key size
	 up to 56 bits

     Salt size
	 12 bits

     Processing cost parameter
	 25

   NT
     The hashing method used for network authentication in some versions of
     the SMB/CIFS protocol.  Available, for cross-compatibility's sake, on
     FreeBSD.  Based on MD4.  Has no salt or tunable cost parameter.  It is so
     weak that almost any human-chosen passphrase hashed with this method is
     guessable.	 It should only be used if you absolutely have to generate
     hashes that will work on an old operating system that supports nothing
     else.

     Prefix
	 "$3$"

     Hashed passphrase format
	 \$3\$\$[0-9a-f]{32}

     Maximum passphrase length
	 unlimited

     Hash size
	 256 bits

     Salt size
	 0 bits

     Processing cost parameter
	 1

SEE ALSO
     crypt(3), crypt_gensalt(3), getpwent(3), passwd(5), shadow(5), pam(8)

     Niels Provos and David Mazieres, “A Future-Adaptable Password Scheme”,
     Proceedings of the 1999 USENIX Annual Technical Conference,
     https://www.usenix.org/events/usenix99/provos.html, June 1999.

     Robert Morris and Ken Thompson, “Password Security: A Case History”,
     Communications of the ACM, 11, 22,
     http://wolfram.schneider.org/bsd/7thEdManVol2/password/password.pdf,
     1979.

Openwall Project		March 27, 2024		      Openwall Project