gno/usr.man/man3/crypt.3

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.\"     @(#)crypt.3	8.2 (Berkeley) 12/11/93
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.TH CRYPT 3 "28 January 1997" GNO "Library Routines"
.SH NAME
.BR crypt ,
.BR setkey ,
.BR encrypt ,
\- simple encryption
.SH SYNOPSIS
#include <unistd.h>
.sp 1
char
*\fBcrypt\fR (const char *\fIkey\fR, const char *\fIsalt\fR);
.br
int
\fBsetkey\fR (char *\fIkey\fR);
.br
int
\fBencrypt\fR (char *\fIblock\fR, int \fIflag\fR);
.SH DESCRIPTION
The
.BR crypt 
function
performs password encryption.
It is derived from an algorithm given in 
.I "Computer Networks"
by Andy Tanenbaum.
.LP
The first argument to
.BR crypt
.RI ( key )
is a
.BR NULL -terminated
string (normally a password typed by a user).
The second,
.IR salt ,
is a two-character array that should be randomly generated by the caller
in the case of encrypting a new password, or should be taken as the
first two characters of the 
.BR /etc/passwd
password entry in the case of validating a password.
.LP
The
functions,
.BR encrypt
and
.BR setkey 
allow limited access to the encryption
algorithm itself.
The
.IR key
argument to
.BR setkey 
is a 64 character array of
binary values (numeric 0 or 1).
A 56-bit key is derived from this array by dividing the array
into groups of 8 and ignoring the last bit in each group.
.LP
The
.BR encrypt 
argument
.I block
is also a 64 character array of
binary values.
If the value of
.I flag
is 0,
the argument
.I block
is encrypted, otherwise it
is decrypted.
The encryption or decryption is returned in the original
array
.I block
after using the
key specified
by
.BR setkey 
to process it.
.LP
The function
.BR crypt 
returns a pointer to the encrypted value (which is formatted as 
printable ASCII characters) on success and NULL on failure.
The functions
.BR setkey 
and
.BR encrypt 
return 0 on success and 1 on failure.
.LP
Use of these routines requires linking with the 
.BR libcrypt
library.
.SH SEE ALSO
.BR login (1),
.BR passwd (1),
.BR getpass (3),
.BR passwd (5)
.sp
.RS
.I "Mathematical Cryptology for Computer Scientists and Mathematicians"
by
Wayne Patterson.
1987.
Volume ISBN 0-8476-7438-X.
.RE
.sp 1
.RS
.I "Password Security: A Case History"
by
R. Morris,
Ken Thompson.
.IR "Communications of the ACM" ,
vol. 22, pp. 594-597.  November 1979.
.RE
.sp 1
.RS
.I "DES will be Totally Insecure within Ten Years"
by
M.E. Hellman.
.IR "IEEE Spectrum" ,
vol. 16, pp. 32-39.  July 1979.
.RE
.SH BUGS
The
.BR crypt 
function leaves its result in an internal static object and returns
a pointer to that object.
Subsequent calls to
.BR crypt 
will modify the same object.