.\" $OpenBSD: skey.3,v 1.14 2015/09/10 17:55:21 schwarze Exp $
.\"
.\" Copyright (c) 2001 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: September 10 2015 $
.Dt SKEY 3
.Os
.Sh NAME
.Nm atob8 ,
.Nm backspace ,
.Nm btoa8 ,
.Nm btoe ,
.Nm etob ,
.Nm f ,
.Nm htoi ,
.Nm keycrunch ,
.Nm put8 ,
.Nm readpass ,
.Nm readskey ,
.Nm rip ,
.Nm sevenbit ,
.Nm skey_authenticate ,
.Nm skey_get_algorithm ,
.Nm skey_haskey ,
.Nm skey_keyinfo ,
.Nm skey_passcheck ,
.Nm skey_set_algorithm ,
.Nm skey_unlock ,
.Nm skeychallenge ,
.Nm skeychallenge2 ,
.Nm skeygetnext ,
.Nm skeylookup ,
.Nm skeyverify ,
.Nm skipspace
.Nd S/Key library functions
.Sh SYNOPSIS
.In skey.h
.Ft int
.Fn atob8 "char *out" "char *in"
.Ft void
.Fn backspace "char *buf"
.Ft int
.Fn btoa8 "char *out" "char *in"
.Ft char *
.Fn btoe "char *engout" "char *c"
.Ft int
.Fn etob "char *out" "char *e"
.Ft void
.Fn f "char *x"
.Ft int
.Fn htoi "int h"
.Ft int
.Fn keycrunch "char *result" "char *seed" "char *passwd"
.Ft char *
.Fn put8 "char *out" "char *s"
.Ft char *
.Fn readpass "char *buf" "int n"
.Ft char *
.Fn readskey "char *buf" "int n"
.Ft void
.Fn rip "char *buf"
.Ft void
.Fn sevenbit "char *s"
.Ft int
.Fn skey_authenticate "char *user"
.Ft const char *
.Fn skey_get_algorithm "void"
.Ft int
.Fn skey_haskey "char *user"
.Ft char *
.Fn skey_keyinfo "char *user"
.Ft int
.Fn skey_passcheck "char *user" "char *passwd"
.Ft char *
.Fn skey_set_algorithm "char *new"
.Ft int
.Fn skey_unlock "struct skey *rec"
.Ft int
.Fn skeychallenge "struct skey *rec" "char *user" "char *buf"
.Ft int
.Fn skeychallenge2 "int fd" "struct skey *rec" "char *user" "char *buf"
.Ft int
.Fn skeygetnext "struct skey *rec"
.Ft int
.Fn skeylookup "struct skey *rec" "char *user"
.Ft int
.Fn skeyverify "struct skey *rec" "char *response"
.Ft char *
.Fn skipspace "char *"
.Sh DESCRIPTION
These functions implement the S/Key one time password authentication
mechanism.
.Pp
The
.Fn atob8
function converts the 16-byte hex string
.Fa in
to an 8-byte binary array stored in
.Fa out .
The
.Fn atob8
function returns 0 on success and \-1 if an invalid hex character is encountered.
.Pp
The
.Fn backspace
function removes backspaced over characters from
.Fa buf .
Note that
.Fn backspace
assumes the actual backspace character is 0x8 (^H).
.Pp
The
.Fn btoa8
function converts the 8-byte binary array
.Fa in
to a 16-byte string of hex digits stored in
.Fa out ;
the caller must supply enough space (17 bytes including the final NUL).
The
.Fn btoa8
function returns 0 on success and \-1 if an error occurred.
.Pp
The
.Fn btoe
function encodes the 8 bytes in
.Fa c
into a string of 6 English words, stored in
.Fa engout .
The caller must supply enough space (30 bytes including the final NUL)
to store the words.
The
.Fn btoe
function returns
.Fa engout .
.Pp
The
.Fn etob
function converts the 6 English words in
.Fa e
into an 8-byte binary representation.
The
.Fn etob
function returns 1 if the words are all in the database and parity is correct,
0 if a word is not in the database, \-1 if the number of words is incorrect,
or \-2 if there is a parity error.
.Pp
The
.Fn f
function is a one-way hash that overwrites the 8-byte input buffer
.Fa x
with the hashed result.
.Pp
The
.Fn htoi
function converts a single hex digit
.Fa h
to an integer.
The
.Fn htoi
function returns the converted integer on success or \-1 if
.Fa h
not a valid hex digit.
.Pp
The
.Fn keycrunch
function concatenates the
.Fa seed
and
.Fa passwd ,
runs them through a hash function and collapses the
.Fa result
to 64 bits.
The
.Fn keycrunch
function returns 0 on success or \-1 if there is a memory allocation failure.
.Pp
The
.Fn put8
function converts the 8 bytes stored in
.Fa s
into a series of 4 16-bit hex digit stored in
.Fa out .
There must be at least 20 bytes (including the NUL) in the output buffer,
.Fa out .
The
.Fn put8
function returns
.Fa out .
.Pp
The
.Fn readpass
function reads up to
.Fa n
characters from standard input with echo turned off, converting the
resulting string to 7 bits, storing the result in
.Fa buf .
The
.Fn readpass
function returns
.Fa buf .
.Pp
The
.Fn readskey
function reads up to
.Fa n
characters from standard input with echo turned on, converting the
resulting string to 7 bits, storing the result in
.Fa buf .
The
.Fn readskey
function returns
.Fa buf .
.Pp
The
.Fn rip
function strips trailing linefeeds and carriage returns from
.Fa buf .
.Pp
The
.Fn sevenbit
function strips the high bit from each character in
.Fa s ,
converting the characters to seven bit ASCII.
.Pp
The
.Fn skey_authenticate
function presents the
.Fa user
with an S/Key challenge and authenticates the response.
The
.Fn skey_authenticate
function returns 0 if authentication is successful or \-1 if not.
.Pp
The
.Fn skey_get_algorithm
function returns a string corresponding to the hash algorithm for
the current user.
The default algorithm is
.Dq md5 .
.Pp
The
.Fn skey_haskey
function returns 0 if the
.Fa user
exists in the S/Key database, 1 if the user does not exist, or \-1
if there was an error reading the database.
.Pp
The
.Fn skey_keyinfo
function returns a string containing the current sequence number and seed for
.Fa user .
The returned string points to internal static storage that will be
overwritten by subsequent calls to
.Fn skey_keyinfo .
.Pp
The
.Fn skey_passcheck
function checks a
.Fa user
and
.Fa passwd
pair against the S/Key database.
It returns 0 on successful authentication or \-1 on failure.
.Pp
The
.Fn skey_set_algorithm
function sets the user's hash algorithm based on the string
.Fa new .
The
.Fn skey_set_algorithm
function returns the specified algorithm if it is supported,
or the null pointer if the hash algorithm is not supported.
.Pp
The
.Fn skey_unlock
function unlocks the record in the S/Key database specified by
.Fa rec .
The
.Fn skey_unlock
function returns 0 on success or \-1 on failure.
Either way, the S/Key database is not closed nor is the database
file pointer affected.
.Pp
The
.Fn skeychallenge
function stores the (potentially fake) S/Key challenge for
.Fa user
in
.Fa buf ,
which is at least SKEY_MAX_CHALLENGE bytes long.
It also fills in the skey struct
.Fa rec
and locks the user's record in the S/Key database.
The
.Fn skeychallenge
function returns 0 on success or \-1 on failure.
On success the S/Key database remains open and the read/write file
pointer is set to the beginning of the record.
.Pp
The
.Fn skeychallenge2
function is identical to
.Fn skeychallenge
except that instead of opening the user's entry in the S/Key database,
the open file referenced by
.Ar fd
is used instead.
When
.Ar fd
is \-1, the behavior is equivalent to
.Fn skeychallenge .
.Pp
The
.Fn skeygetnext
function stores the next record in the S/Key database in
.Fa rec
and locks that record in the S/Key database.
The
.Fn skeygetnext
function returns 0 on success, 1 if there are no more entries,
or \-1 if there was an error accessing the S/Key database.
The S/Key database remains open after a call to
.Fn skeygetnext .
If no error was encountered accessing the S/Key database, the read/write
file pointer is set to the beginning of the record or at EOF if
there are no more records.
.br
Because it exposes other users' S/Key records, only the superuser may use
.Fn skeygetnext .
.Pp
The
.Fn skeylookup
function looks up the specified
.Fa user
in the S/Key database then fills in the skey struct
.Fa rec
and locks the user's record in the database.
The
.Fn skeylookup
function returns 0 on success, 1 if
.Fa user
was not found, or \-1 if there was an error accessing the S/Key database.
If no error was encountered accessing the S/Key database, the read/write
file pointer is set to the beginning of the record.
.Pp
The
.Fn skeyverify
function verifies the user's
.Fa response
based on the S/Key record
.Fa rec .
It returns 0 on success (updating the database), 1 on failure, or
\-1 if there was an error accessing the database.
The database is always closed by a call to
.Fn skeyverify .
.Sh SEE ALSO
.Xr skey 1 ,
.Xr skeyinit 1
.Sh STANDARDS
There is no standard API for S/Key.
The de facto standard is the free S/Key distribution released by Bellcore.
.Pp
The following functions are extensions and do not appear in
the original Bellcore S/Key distribution:
.Fn readskey ,
.Fn skey_authenticate ,
.Fn skey_get_algorithm ,
.Fn skey_haskey ,
.Fn skey_keyinfo ,
.Fn skey_passcheck ,
.Fn skey_set_algorithm ,
.Fn skey_unlock .
.Pp
S/Key is a Trademark of Bellcore.