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134 lines
4.7 KiB
Bash
134 lines
4.7 KiB
Bash
# $OpenBSD: limit-keytype.sh,v 1.10 2021/02/25 03:27:34 djm Exp $
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# Placed in the Public Domain.
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tid="restrict pubkey type"
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# XXX sk-* keys aren't actually tested ATM.
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rm -f $OBJ/authorized_keys_$USER $OBJ/user_ca_key* $OBJ/user_key*
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rm -f $OBJ/authorized_principals_$USER $OBJ/cert_user_key*
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mv $OBJ/sshd_proxy $OBJ/sshd_proxy.orig
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mv $OBJ/ssh_proxy $OBJ/ssh_proxy.orig
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ktype1=ed25519; ktype2=ed25519; ktype3=ed25519;
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ktype4=ed25519; ktype5=ed25519; ktype6=ed25519;
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for t in $SSH_KEYTYPES ; do
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case "$t" in
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ssh-rsa) ktype2=rsa ;;
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ecdsa*) ktype3=ecdsa ;; # unused
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ssh-dss) ktype4=dsa ;;
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sk-ssh-ed25519@openssh.com) ktype5=ed25519-sk ;;
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sk-ecdsa-sha2-nistp256@openssh.com) ktype6=ecdsa-sk ;;
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esac
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done
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# Create a CA key
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${SSHKEYGEN} -q -N '' -t $ktype1 -f $OBJ/user_ca_key ||\
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fatal "ssh-keygen failed"
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# Make some keys and a certificate.
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${SSHKEYGEN} -q -N '' -t $ktype1 -f $OBJ/user_key1 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -N '' -t $ktype2 -f $OBJ/user_key2 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -N '' -t $ktype2 -f $OBJ/user_key3 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -N '' -t $ktype4 -f $OBJ/user_key4 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -N '' -t $ktype5 -f $OBJ/user_key5 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -N '' -t $ktype6 -f $OBJ/user_key6 || \
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fatal "ssh-keygen failed"
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${SSHKEYGEN} -q -s $OBJ/user_ca_key -I "regress user key for $USER" \
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-z $$ -n ${USER},mekmitasdigoat $OBJ/user_key3 ||
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fatal "couldn't sign user_key1"
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# Copy the private key alongside the cert to allow better control of when
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# it is offered.
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mv $OBJ/user_key3-cert.pub $OBJ/cert_user_key3.pub
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grep -v IdentityFile $OBJ/ssh_proxy.orig > $OBJ/ssh_proxy
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opts="-oProtocol=2 -F $OBJ/ssh_proxy -oIdentitiesOnly=yes"
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certopts="$opts -i $OBJ/user_key3 -oCertificateFile=$OBJ/cert_user_key3.pub"
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echo mekmitasdigoat > $OBJ/authorized_principals_$USER
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cat $OBJ/user_key1.pub > $OBJ/authorized_keys_$USER
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cat $OBJ/user_key2.pub >> $OBJ/authorized_keys_$USER
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prepare_config() {
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(
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grep -v "Protocol" $OBJ/sshd_proxy.orig
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echo "Protocol 2"
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echo "AuthenticationMethods publickey"
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echo "TrustedUserCAKeys $OBJ/user_ca_key.pub"
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echo "AuthorizedPrincipalsFile $OBJ/authorized_principals_%u"
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for x in "$@" ; do
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echo "$x"
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done
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) > $OBJ/sshd_proxy
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}
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# Return the required parameter for PubkeyAcceptedAlgorithms corresponding to
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# the supplied key type.
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keytype() {
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case "$1" in
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ecdsa) printf "ecdsa-sha2-*" ;;
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ed25519) printf "ssh-ed25519" ;;
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dsa) printf "ssh-dss" ;;
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rsa) printf "rsa-sha2-256,rsa-sha2-512,ssh-rsa" ;;
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sk-ecdsa) printf "sk-ecdsa-*" ;;
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sk-ssh-ed25519) printf "sk-ssh-ed25519-*" ;;
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esac
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}
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prepare_config
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# Check we can log in with all key types.
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${SSH} $certopts proxy true || fatal "cert failed"
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${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed"
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${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed"
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# Allow plain Ed25519 and RSA. The certificate should fail.
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verbose "allow $ktype2,$ktype1"
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prepare_config \
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"PubkeyAcceptedAlgorithms `keytype $ktype2`,`keytype $ktype1`"
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${SSH} $certopts proxy true && fatal "cert succeeded"
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${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed"
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${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed"
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# Allow Ed25519 only.
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verbose "allow $ktype1"
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prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype1`"
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${SSH} $certopts proxy true && fatal "cert succeeded"
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${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed"
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if [ "$ktype1" != "$ktype2" ]; then
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${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded"
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fi
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# Allow all certs. Plain keys should fail.
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verbose "allow cert only"
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prepare_config "PubkeyAcceptedAlgorithms *-cert-v01@openssh.com"
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${SSH} $certopts proxy true || fatal "cert failed"
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${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded"
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${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded"
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# Allow RSA in main config, Ed25519 for non-existent user.
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verbose "match w/ no match"
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prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype2`" \
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"Match user x$USER" "PubkeyAcceptedAlgorithms +`keytype $ktype1`"
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${SSH} $certopts proxy true && fatal "cert succeeded"
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if [ "$ktype1" != "$ktype2" ]; then
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${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded"
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fi
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${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed"
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# Allow only DSA in main config, Ed25519 for user.
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verbose "match w/ matching"
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prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype4`" \
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"Match user $USER" "PubkeyAcceptedAlgorithms +`keytype $ktype1`"
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${SSH} $certopts proxy true || fatal "cert failed"
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${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed"
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${SSH} $opts -i $OBJ/user_key4 proxy true && fatal "key4 succeeded"
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