72 lines
1.8 KiB
Groff
72 lines
1.8 KiB
Groff
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.TH CRYPT 3
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.SH NAME
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crypt \- one-way password encryption function
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.SH SYNOPSIS
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.ft B
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.nf
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#define _MINIX_SOURCE 1
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#include <unistd.h>
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char *crypt(const char *\fIkey\fP, const char *\fIsalt\fP)
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.fi
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.ft P
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.SH DESCRIPTION
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The first use of
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.B crypt()
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is to encrypt a password. Its second use is to authenticate a shadow
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password. In both cases
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.B crypt()
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calls
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.BR pwdauth (8)
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to do the real work.
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.PP
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.B Crypt()
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encrypts a password if called with a user typed key, and a salt
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whose first two characters are in the set [./0-9A-Za-z]. The result is a
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character string in the [./0-9A-Za-z] alphabet of which the first two
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characters are equal to the salt, and the rest is the result of encrypting
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the key and the salt.
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.PP
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If
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.B crypt()
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is called with a salt that has the form
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.BI "##" user
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then the key is encrypted and compared to the encrypted password of
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.I user
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in the shadow password file. If they are equal then
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.B crypt()
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returns the
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.BI "##" user
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argument, if not then some other string is returned. This trick assures
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that the normal way to authenticate a password still works:
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.PP
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.RS
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.nf
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if (strcmp(pw->pw_passwd, crypt(key, pw->pw_passwd))) ...
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.fi
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.RE
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.PP
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If
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.I key
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is a null string, and the shadow password is a null string or the salt is a
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null string then the result equals
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.IR salt .
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(This is because the caller can't tell if a password field is empty in the
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shadow password file.)
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.PP
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The key and salt are limited to 1024 bytes total including the null bytes.
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.SH FILES
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.TP 25
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/usr/lib/pwdauth
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The password authentication program
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.SH "SEE ALSO"
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.BR getpass (3),
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.BR getpwent (3),
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.BR passwd (5),
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.BR pwdauth (8).
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.SH NOTES
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The result of an encryption is returned in a static array that is
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overwritten by each call. The return value should not be modified.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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