58 lines
1.8 KiB
Groff
58 lines
1.8 KiB
Groff
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.SH NAME
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pwdauth \- password authentication program
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.SH SYNOPSIS
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.B /usr/lib/pwdauth
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.SH DESCRIPTION
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.B Pwdauth
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is a program that is used by the
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.BR crypt (3)
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function to do the hard work. It is a setuid root utility so that it is
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able to read the shadow password file.
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.PP
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.B Pwdauth
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expects on standard input two null terminated strings, the
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password typed by the user, and the salt. That is, the two arguments of
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the
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.B crypt
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function. The input read in a single read call must be 1024 characters or
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less including the nulls.
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.B Pwdauth
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takes one of two actions depending on the salt.
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.PP
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If the salt has the form "\fB##\fIuser\fR" then the
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.I user
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is used to index the shadow password file to obtain the encrypted password.
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The input password is encrypted with the one-way encryption function
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contained within
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.B pwdauth
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and compared to the encrypted password from the shadow password file. If
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equal then
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.B pwdauth
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returns the string "\fB##\fIuser\fR" with exit code 0, otherwise exit
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code 2 to signal failure. The string "\fB##\fIuser\fR" is also returned
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if both the shadow password and the input password are null strings to
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allow a password-less login.
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.PP
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If the salt is not of the form "\fB##\fIuser\fR" then the password is
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encrypted and the result of the encryption is returned. If salt and
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password are null strings then a null string is returned.
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.PP
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The return value is written to standard output as a null terminated string
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of 1024 characters or less including the null.
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.PP
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The exit code is 1 on any error.
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.SH "SEE ALSO"
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.BR crypt (3),
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.BR passwd (5).
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.SH NOTES
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A password must be checked like in this example:
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.PP
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.RS
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pw_ok = (strcmp(crypt(key, pw->pw_passwd), pw->pw_passwd) == 0);
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.RE
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.PP
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The second argument of crypt must be the entire encrypted password and
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not just the two character salt.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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