xref: /openbsd-src/lib/libc/crypt/crypt.3 (revision f0e1d4849b87db33ce0be414511d728bb1f5c71e)

.\" $OpenBSD: crypt.3,v 1.46 2025/01/09 23:18:08 jsg Exp $
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.\" FreeSec: libcrypt
.\"
.\" Copyright (c) 1994 David Burren
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.\" Manual page, using -mandoc macros
.\"
.Dd $Mdocdate: January 9 2025 $
.Dt CRYPT 3
.Os
.Sh NAME
.Nm crypt ,
.Nm bcrypt_gensalt ,
.Nm bcrypt
.Nd password hashing
.Sh SYNOPSIS
.In stdlib.h
.Pp
.In unistd.h
.Ft char *
.Fn crypt "const char *key" "const char *setting"
.In pwd.h
.Ft char *
.Fn bcrypt_gensalt "u_int8_t log_rounds"
.Ft char *
.Fn bcrypt "const char *key" "const char *salt"
.Sh DESCRIPTION
These functions are deprecated in favor of
.Xr crypt_checkpass 3
and
.Xr crypt_newhash 3 .
.Pp
The
.Fn crypt
function performs password hashing.
Additional code has been added to deter key search attempts and to use
stronger hashing algorithms.
.Pp
The first argument to
.Fn crypt
is a NUL-terminated
string
.Fa key ,
typically a user's typed password.
The second,
.Fa setting ,
currently supports a single form.
If it begins
with a string character
.Pq Ql $
and a number then a different algorithm is used depending on the number.
At the moment
.Ql $2
chooses Blowfish hashing; see below for more information.
.Ss Blowfish crypt
The Blowfish version of crypt has 128 bits of
.Fa salt
in order to make building dictionaries of common passwords space consuming.
The initial state of the
Blowfish cipher is expanded using the
.Fa salt
and the
.Fa password
repeating the process a variable number of rounds, which is encoded in
the password string.
The maximum password length is 72.
The final Blowfish password entry is created by encrypting the string
.Pp
.Dq OrpheanBeholderScryDoubt
.Pp
with the Blowfish state 64 times.
.Pp
The version number, the logarithm of the number of rounds and
the concatenation of salt and hashed password are separated by the
.Ql $
character.
An encoded
.Sq 8
would specify 256 rounds.
A valid Blowfish password looks like this:
.Pp
.Dq $2b$12$FPWWO2RJ3CK4FINTw0Hi8OiPKJcX653gzSS.jqltHFMxyDmmQ0Hqq .
.Pp
The whole Blowfish password string is passed as
.Fa setting
for interpretation.
.Sh RETURN VALUES
The function
.Fn crypt
returns a pointer to the encrypted value on success, and
.Dv NULL
on failure.
.Sh SEE ALSO
.Xr encrypt 1 ,
.Xr login 1 ,
.Xr passwd 1 ,
.Xr blowfish 3 ,
.Xr crypt_checkpass 3 ,
.Xr getpass 3 ,
.Xr passwd 5
.Sh HISTORY
An M-209 based
.Fn crypt
function appeared in
.At v3 .
A DES-based
.Fn crypt
first appeared in
.At v7 .
.Fn bcrypt
first appeared in
.Ox 2.1 .
.Sh BUGS
The
.Fn crypt
function returns a pointer to static data, and subsequent calls to
.Fn crypt
will modify the same object.