# $OpenBSD: limit-keytype.sh,v 1.4 2015/10/29 08:05:17 djm Exp $ # Placed in the Public Domain. tid="restrict pubkey type" rm -f $OBJ/authorized_keys_$USER $OBJ/user_ca_key* $OBJ/user_key* rm -f $OBJ/authorized_principals_$USER $OBJ/cert_user_key* mv $OBJ/sshd_proxy $OBJ/sshd_proxy.orig mv $OBJ/ssh_proxy $OBJ/ssh_proxy.orig # Create a CA key ${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_ca_key ||\ fatal "ssh-keygen failed" # Make some keys and a certificate. ${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_key1 || \ fatal "ssh-keygen failed" ${SSHKEYGEN} -q -N '' -t rsa -f $OBJ/user_key2 || \ fatal "ssh-keygen failed" ${SSHKEYGEN} -q -N '' -t rsa -f $OBJ/user_key3 || \ fatal "ssh-keygen failed" ${SSHKEYGEN} -q -N '' -t dsa -f $OBJ/user_key4 || \ fatal "ssh-keygen failed" ${SSHKEYGEN} -q -s $OBJ/user_ca_key -I "regress user key for $USER" \ -z $$ -n ${USER},mekmitasdigoat $OBJ/user_key3 || fatal "couldn't sign user_key1" # Copy the private key alongside the cert to allow better control of when # it is offered. mv $OBJ/user_key3-cert.pub $OBJ/cert_user_key3.pub grep -v IdentityFile $OBJ/ssh_proxy.orig > $OBJ/ssh_proxy opts="-oProtocol=2 -F $OBJ/ssh_proxy -oIdentitiesOnly=yes" certopts="$opts -i $OBJ/user_key3 -oCertificateFile=$OBJ/cert_user_key3.pub" echo mekmitasdigoat > $OBJ/authorized_principals_$USER cat $OBJ/user_key1.pub > $OBJ/authorized_keys_$USER cat $OBJ/user_key2.pub >> $OBJ/authorized_keys_$USER prepare_config() { ( grep -v "Protocol" $OBJ/sshd_proxy.orig echo "Protocol 2" echo "AuthenticationMethods publickey" echo "TrustedUserCAKeys $OBJ/user_ca_key.pub" echo "AuthorizedPrincipalsFile $OBJ/authorized_principals_%u" for x in "$@" ; do echo "$x" done ) > $OBJ/sshd_proxy } prepare_config # Check we can log in with all key types. ${SSH} $certopts proxy true || fatal "cert failed" ${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" ${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" # Allow plain Ed25519 and RSA. The certificate should fail. verbose "allow rsa,ed25519" prepare_config "PubkeyAcceptedKeyTypes ssh-rsa,ssh-ed25519" ${SSH} $certopts proxy true && fatal "cert succeeded" ${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" ${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" # Allow Ed25519 only. verbose "allow ed25519" prepare_config "PubkeyAcceptedKeyTypes ssh-ed25519" ${SSH} $certopts proxy true && fatal "cert succeeded" ${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" ${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded" # Allow all certs. Plain keys should fail. verbose "allow cert only" prepare_config "PubkeyAcceptedKeyTypes ssh-*-cert-v01@openssh.com" ${SSH} $certopts proxy true || fatal "cert failed" ${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded" ${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded" # Allow RSA in main config, Ed25519 for non-existent user. verbose "match w/ no match" prepare_config "PubkeyAcceptedKeyTypes ssh-rsa" \ "Match user x$USER" "PubkeyAcceptedKeyTypes +ssh-ed25519" ${SSH} $certopts proxy true && fatal "cert succeeded" ${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded" ${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" # Allow only DSA in main config, Ed25519 for user. verbose "match w/ matching" prepare_config "PubkeyAcceptedKeyTypes ssh-dss" \ "Match user $USER" "PubkeyAcceptedKeyTypes +ssh-ed25519" ${SSH} $certopts proxy true || fatal "cert failed" ${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" ${SSH} $opts -i $OBJ/user_key4 proxy true && fatal "key4 succeeded"