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# cassh - Manager for an OpenSSH Certification Authority
#
# Written in 2022 by Lucas
#
# To the extent possible under law, the author(s) have dedicated all
# copyright and related and neighboring rights to this software to the
# public domain worldwide. This software is distributed without any
# warranty.
#
# You should have received a copy of the CC0 Public Domain Dedication
# along with this software. If not, see
# <http://creativecommons.org/publicdomain/zero/1.0/>.
.POSIX:
.SUFFIXES:
.SUFFIXES: .sh
.sh:
cp $< $@
chmod a+x $@
P = cassh
V = 0
PREFIX = /usr/local
MANPREFIX = ${PREFIX}/man
BIN = cassh
MAN1 = ${BIN:=.1}
SRC = ${BIN:=.sh} ${MAN1}
DIST = ${SRC} COPYING Makefile README
all: ${BIN}
test: all
prove -p
clean:
rm -f ${BIN} ${P}-${V}.tgz
dist: clean
pax -ws ',^,${P}-${V}/,' ${DIST} | gzip >${P}-${V}.tgz
install: all
mkdir -p ${PREFIX}/bin
cp -f ${BIN} ${PREFIX}/bin
cd ${PREFIX}/bin && chmod 555 ${BIN}
mkdir -p ${MANPREFIX}/man1
cp -f ${MAN1} ${MANPREFIX}/man1
cd ${MANPREFIX}/man1 && chmod 444 ${MAN1}
uninstall:
cd ${PREFIX}/bin && rm -f ${BIN}
cd ${MANPREFIX}/man1 && rm -f ${MAN1}

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cassh
=====
Manager for an OpenSSH Certification Authority.

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.\" cassh - Manager for an OpenSSH Certification Authority
.\"
.\" Written in 2022 by Lucas
.\"
.\" To the extent possible under law, the author(s) have dedicated all
.\" copyright and related and neighboring rights to this software to the
.\" public domain worldwide. This software is distributed without any
.\" warranty.
.\"
.\" You should have received a copy of the CC0 Public Domain Dedication
.\" along with this software. If not, see
.\" <http://creativecommons.org/publicdomain/zero/1.0/>.
.\"
.Dd March 01, 2022
.Dt CASSH 1
.Os
.Sh NAME
.Nm cassh
.Nd Manager for an OpenSSH Certification Authority
.Sh SYNOPSIS
.Nm
.Bk -words
.Cm issue
.Op Fl hqv
.Op Fl I Ar key_id
.Op Fl n Ar principals
.Op Fl V Ar validity_interval
.Ek
.Nm
.Bk -words
.Cm mkfile
.Ic authorized_keys
.Op options
.Ek
.Nm
.Bk -words
.Cm mkfile
.Ic known_hosts
.Op hostnames
.Ek
.Sh DESCRIPTION
.Nm
is a small utility for issuing and revoking OpenSSH Certificates.
It relies on a simple filesystem structure and a running
.Xr ssh-agent 1
instance that is in charge of performing all signing operations.
Additionally,
.Nm
can generate
.Pa authorized_keys
and
.Pa known_hosts
files based on the active Certification Authority.
.Pp
A Certification Authority directory consists of a
.Pa ca.pub
file corresponding to the public key of it, a
.Pa pubkeys/
directory which holds the public keys to be signed, and an optional
.Pa serial.txt
file holding the current serial number for the issued certificates.
.Pp
The following commands are available to
.Xr cassh 1 :
.Bl -tag -width Ds
.It Xo
.Cm issue
.Op Fl hqv
.Op Fl I Ar key_id
.Op Fl n Ar principals
.Op Fl V Ar validity_interval
.Xc
Issue certificates for all the public keys inside the
.Pa pubkeys/
directory.
Token expansion is performed on arguments
.Ar key_id
and
.Ar principals .
The recognized tokens are:
.Pp
.Bl -tag -width XXXX -offset indent -compact
.It %%
A literal
.Sq % .
.It \&%C
The Certification Authority private key comment.
.It %f
The basename of the public key being signed.
.El
.Pp
.Ar key_id
accepts the tokens %%, %C, and %f.
.Pp
.Ar principals
accepts the tokens %% and %f.
.Pp
After token expansion, all recognized options are passed down to
.Xr ssh-keygen 1
process.
.It Cm mkfile Ic authorized_keys Op Ar options
Write an
.Ic authorized_keys
file on standard output corresponding to the current Certification
Authority.
.Ar options
is copied verbatim to the output, and
.Cm cert-authority
is always added.
.It Cm mkfile Ic known_hosts Op Ar hostnames
Write a
.Ic known_hosts
file on standard output corresponding to the current Certification
Authority.
.Ar hostnames is copied verbatim to the output.
.El
.Sh ENVIRONMENT
TBD
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
TBD
.Sh SEE ALSO
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1
.Sh AUTHORS
.An Lucas
.Sh LICENSE
.Nm
is in the public domain.
.Pp
To the extent possible under law, the author(s) have dedicated all
copyright and related and neighboring rights to this software to the
public domain worldwide.
.Pp
.Lk http://creativecommons.org/publicdomain/zero/1.0/

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#!/bin/sh
# cassh - Manager for an OpenSSH Certification Authority
#
# Written in 2022 by Lucas
#
# To the extent possible under law, the author(s) have dedicated all
# copyright and related and neighboring rights to this software to the
# public domain worldwide. This software is distributed without any
# warranty.
# You should have received a copy of the CC0 Public Domain Dedication
# along with this software. If not, see
# <http://creativecommons.org/publicdomain/zero/1.0/>.
usage()
{
cat - <<EOF >&2
Usage:
${0##*/} issue [-hqv] [-I key_id] [-n principals]
[-V validity_interval]
${0##*/} mkfile [-n principals] authorized_keys | known_hosts
EOF
exit 1
}
err()
{
printf "%s: %s\n" "${0##*/}" "$*" >&2
exit 1
}
strip_leading_zeros()
{
_s=$1
if [ -z "$_s" ]; then
return
fi
while [ X"${_s#0}" != X"$_s" ]; do
_s=${_s#0}
done
echo "${_s:-0}"
}
strcmp()
{
_r=$(expr "X$1" "$2" "X$3")
[ "${_r:-0}" -eq 1 ]
}
# Returns comment from the ssh-agent if any is returned, otherwise it
# returns the public key's fingerprint.
get_ca_comment_from_sk()
{
ssh-keygen -lf "$1" | {
read -r pk_sz pk_fp pk_extra
_comment=$(ssh-add -l | while read -r sk_sz sk_fp sk_extra; do
if [ "X$sk_fp" = "X$pk_fp" ]; then
echo "${sk_extra% (*)}"
break
fi
done)
echo "${_comment:-${pk_fp#*:}}"
}
}
_template_fmt()
{
_allowed_chars=$1
_char=$2
if [ "X$_char" = X% ]; then
echo %
return $?
fi
case $_char in
[$_allowed_chars])
;;
*)
return 1
;;
esac
_v=$(eval echo '${_template_fmt_'"$_char"':-}')
if [ -z "$_v" ]; then
return 1
fi
echo "$_v"
}
template()
{
_allowed=$1
_s=$2
_out=
while [ "${_s#*%}" != "$_s" ]; do
_t=${_s#*%}
_out=$_out${_s%"%"$_t}
_s=$_t
_c=${_s%${_s#?}}
_t=$(_template_fmt "$_allowed" "$_c")
if [ $? -ne 0 ]; then
return 1
fi
_out=$_out$_t
_s=${_s#$_c}
done
_out=$_out$_s
echo "$_out"
}
main_issue()
{
hflag=
key_id_fmt=%C/%f
nflag=false
principals_fmt=
qflag=
validity_interval=always:forever
vflag=
while getopts hI:n:qV:v flag; do
case $flag in
h) hflag=-h ;;
I) key_id_fmt=$OPTARG ;;
n) nflag=true principals_fmt=$OPTARG ;;
q) qflag=-q ;;
V) validity_interval=$OPTARG ;;
v) vflag=${vflag:--}v ;;
*) usage ;;
esac
done
shift $(($OPTIND - 1))
if [ $# -ne 0 ]; then
usage
fi
if [ ! -f ca.pub ]; then
err "no ca.pub found"
fi
if ! ssh-add $qflag $vflag -T ca.pub; then
err "can't use CA key"
fi
if [ ! -d pubkeys/ ]; then
err "no pubkeys directory found"
fi
if [ ! -f serial.txt ]; then
date -u +%Y%m%d000000000 >serial.txt
fi
read -r serial <serial.txt
# Remove NNNNNNNNN suffix
serial_date=${serial%?????????}
current_date=$(date -u +%Y%m%d)
if strcmp "$current_date" ">" "$serial_date"; then
serial_date=$current_date
serial_counter=0
else
# Remove YYYYmmdd prefix and leading
serial_counter=$(strip_leading_zeros "${serial#????????}")
fi
serial=$(printf "%s%09u\n" "$serial_date" "$serial_counter")
_template_fmt_C=$(get_ca_comment_from_sk ca.pub)
find pubkeys/ -type f -name '*.pub' ! -name '*-cert.pub' | {
rc=0
while read -r pk; do
pkname=${pk%.pub}
pkname=${pkname#pubkeys/}
_template_fmt_f=$pkname
id=$(template Cf "$key_id_fmt")
set -- -I "$id" -Us ca.pub $hflag $qflag $vflag \
-V "$validity_interval" -z "$serial"
if $nflag; then
principals=$(template f "$principals_fmt")
ssh-keygen "$@" -n "$principals" "$pk"
else
ssh-keygen "$@" "$pk"
fi || rc=1
serial_counter=$(($serial_counter + 1))
if [ $serial_counter -ge 1000000000 ]; then
err "can't issue more certificates today"
fi
serial=$(printf "%s%09u\n" "$serial_date" \
"$serial_counter" | tee serial.txt)
if [ $rc -ne 0 ]; then
break
fi
done
return $rc
}
}
main_mkfile()
{
while getopts : flag; do
case $flag in
*) usage ;;
esac
done
shift $(($OPTIND - 1))
if [ $# -lt 1 ]; then
usage
fi
file=$1
shift
if [ ! -f ca.pub ]; then
err "no ca.pub found"
fi
case $file in
authorized_keys)
if [ $# -gt 1 ]; then
usage
fi
options=cert-authority${1:+,$1}
printf "%s " "$options"
;;
known_hosts)
if [ $# -gt 1 ]; then
usage
fi
hostnames=${1:-}
if [ -n "$hostnames" ]; then
printf "@cert-authority %s " "$hostnames"
else
printf "@cert-authority "
fi
;;
*)
err "unknown file \"$file\""
;;
esac
cat ca.pub
}
set -u
if [ $# -lt 1 ]; then
usage
fi
cmd=$1
shift
case $cmd in
issue) main_issue "$@" ;;
mkfile) main_mkfile "$@" ;;
*) usage ;;
esac