1# $OpenBSD: limit-keytype.sh,v 1.10 2021/02/25 03:27:34 djm Exp $ 2# Placed in the Public Domain. 3 4tid="restrict pubkey type" 5 6# XXX sk-* keys aren't actually tested ATM. 7 8rm -f $OBJ/authorized_keys_$USER $OBJ/user_ca_key* $OBJ/user_key* 9rm -f $OBJ/authorized_principals_$USER $OBJ/cert_user_key* 10 11mv $OBJ/sshd_proxy $OBJ/sshd_proxy.orig 12mv $OBJ/ssh_proxy $OBJ/ssh_proxy.orig 13 14ktype1=ed25519; ktype2=ed25519; ktype3=ed25519; 15ktype4=ed25519; ktype5=ed25519; ktype6=ed25519; 16for t in $SSH_KEYTYPES ; do 17 case "$t" in 18 ssh-rsa) ktype2=rsa ;; 19 ecdsa*) ktype3=ecdsa ;; # unused 20 ssh-dss) ktype4=dsa ;; 21 sk-ssh-ed25519@openssh.com) ktype5=ed25519-sk ;; 22 sk-ecdsa-sha2-nistp256@openssh.com) ktype6=ecdsa-sk ;; 23 esac 24done 25 26# Create a CA key 27${SSHKEYGEN} -q -N '' -t $ktype1 -f $OBJ/user_ca_key ||\ 28 fatal "ssh-keygen failed" 29 30# Make some keys and a certificate. 31${SSHKEYGEN} -q -N '' -t $ktype1 -f $OBJ/user_key1 || \ 32 fatal "ssh-keygen failed" 33${SSHKEYGEN} -q -N '' -t $ktype2 -f $OBJ/user_key2 || \ 34 fatal "ssh-keygen failed" 35${SSHKEYGEN} -q -N '' -t $ktype2 -f $OBJ/user_key3 || \ 36 fatal "ssh-keygen failed" 37${SSHKEYGEN} -q -N '' -t $ktype4 -f $OBJ/user_key4 || \ 38 fatal "ssh-keygen failed" 39${SSHKEYGEN} -q -N '' -t $ktype5 -f $OBJ/user_key5 || \ 40 fatal "ssh-keygen failed" 41${SSHKEYGEN} -q -N '' -t $ktype6 -f $OBJ/user_key6 || \ 42 fatal "ssh-keygen failed" 43${SSHKEYGEN} -q -s $OBJ/user_ca_key -I "regress user key for $USER" \ 44 -z $$ -n ${USER},mekmitasdigoat $OBJ/user_key3 || 45 fatal "couldn't sign user_key1" 46# Copy the private key alongside the cert to allow better control of when 47# it is offered. 48mv $OBJ/user_key3-cert.pub $OBJ/cert_user_key3.pub 49 50grep -v IdentityFile $OBJ/ssh_proxy.orig > $OBJ/ssh_proxy 51 52opts="-oProtocol=2 -F $OBJ/ssh_proxy -oIdentitiesOnly=yes" 53certopts="$opts -i $OBJ/user_key3 -oCertificateFile=$OBJ/cert_user_key3.pub" 54 55echo mekmitasdigoat > $OBJ/authorized_principals_$USER 56cat $OBJ/user_key1.pub > $OBJ/authorized_keys_$USER 57cat $OBJ/user_key2.pub >> $OBJ/authorized_keys_$USER 58 59prepare_config() { 60 ( 61 grep -v "Protocol" $OBJ/sshd_proxy.orig 62 echo "Protocol 2" 63 echo "AuthenticationMethods publickey" 64 echo "TrustedUserCAKeys $OBJ/user_ca_key.pub" 65 echo "AuthorizedPrincipalsFile $OBJ/authorized_principals_%u" 66 for x in "$@" ; do 67 echo "$x" 68 done 69 ) > $OBJ/sshd_proxy 70} 71 72# Return the required parameter for PubkeyAcceptedAlgorithms corresponding to 73# the supplied key type. 74keytype() { 75 case "$1" in 76 ecdsa) printf "ecdsa-sha2-*" ;; 77 ed25519) printf "ssh-ed25519" ;; 78 dsa) printf "ssh-dss" ;; 79 rsa) printf "rsa-sha2-256,rsa-sha2-512,ssh-rsa" ;; 80 sk-ecdsa) printf "sk-ecdsa-*" ;; 81 sk-ssh-ed25519) printf "sk-ssh-ed25519-*" ;; 82 esac 83} 84 85prepare_config 86 87# Check we can log in with all key types. 88${SSH} $certopts proxy true || fatal "cert failed" 89${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" 90${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" 91 92# Allow plain Ed25519 and RSA. The certificate should fail. 93verbose "allow $ktype2,$ktype1" 94prepare_config \ 95 "PubkeyAcceptedAlgorithms `keytype $ktype2`,`keytype $ktype1`" 96${SSH} $certopts proxy true && fatal "cert succeeded" 97${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" 98${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" 99 100# Allow Ed25519 only. 101verbose "allow $ktype1" 102prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype1`" 103${SSH} $certopts proxy true && fatal "cert succeeded" 104${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" 105if [ "$ktype1" != "$ktype2" ]; then 106 ${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded" 107fi 108 109# Allow all certs. Plain keys should fail. 110verbose "allow cert only" 111prepare_config "PubkeyAcceptedAlgorithms *-cert-v01@openssh.com" 112${SSH} $certopts proxy true || fatal "cert failed" 113${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded" 114${SSH} $opts -i $OBJ/user_key2 proxy true && fatal "key2 succeeded" 115 116# Allow RSA in main config, Ed25519 for non-existent user. 117verbose "match w/ no match" 118prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype2`" \ 119 "Match user x$USER" "PubkeyAcceptedAlgorithms +`keytype $ktype1`" 120${SSH} $certopts proxy true && fatal "cert succeeded" 121if [ "$ktype1" != "$ktype2" ]; then 122 ${SSH} $opts -i $OBJ/user_key1 proxy true && fatal "key1 succeeded" 123fi 124${SSH} $opts -i $OBJ/user_key2 proxy true || fatal "key2 failed" 125 126# Allow only DSA in main config, Ed25519 for user. 127verbose "match w/ matching" 128prepare_config "PubkeyAcceptedAlgorithms `keytype $ktype4`" \ 129 "Match user $USER" "PubkeyAcceptedAlgorithms +`keytype $ktype1`" 130${SSH} $certopts proxy true || fatal "cert failed" 131${SSH} $opts -i $OBJ/user_key1 proxy true || fatal "key1 failed" 132${SSH} $opts -i $OBJ/user_key4 proxy true && fatal "key4 succeeded" 133 134