.\" $OpenBSD: skey.3,v 1.6 2002/05/24 21:32:40 deraadt Exp $
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.\" Copyright (c) 2001 Todd C. Miller <Todd.Miller@courtesan.com>
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.Dd June 21, 2001
.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 skeygetnext,
.Nm skeylookup,
.Nm skeyverify,
.Nm skipspace
.Nd S/Key library functions
.Sh SYNOPSIS
.Fd #include <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 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
.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
.Tn 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 check 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 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.