This relates to:
x/crypto/ssh: publicKeyCallback cannot handshake using ssh-rsa keys signed using the ssh-rsa-sha2-256 algorithm #39885
I decided to create a new issue even though this is mentioned in the comments for that issue because this is more specifically for server-sig-algs and RFC 8308 support.
What version of Go are you using (go version)?
$ go version
go version go1.16.3 linux/amd64
Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (go env)?
go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/kdavidson/.cache/go-build"
GOENV="/home/kdavidson/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/kdavidson/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/kdavidson/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.3"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4051208766=/tmp/go-build -gno-record-gcc-switches"
What did you do?
Recently, OpenSSH 8.8 deprecated support for ssh-rsa host keys and ssh-rsa pubkey auth as a default value. If users try to connect to a Go x/crypto/ssh server using OpenSSH 8.8 with ssh-rsa for pubkey auth, the client will fail to find a mutual algorithm and not even attempt to send a client's ssh-rsa pubkey auth, likely to avoid any auth penalties.
What did you expect to see?
I would expect the SSH server to send an SSH_MSG_EXT_INFO containing valid pubkey auth algorithms using the server-sig-algs extension, as defined in RFC 8308.
What did you see instead?
The x/crypto SSH server does not send any pubkey auth algorithms, so a client may end up not sending a potentially valid pubkey auth to avoid penalties.
This relates to:
x/crypto/ssh: publicKeyCallback cannot handshake using ssh-rsa keys signed using the ssh-rsa-sha2-256 algorithm #39885
I decided to create a new issue even though this is mentioned in the comments for that issue because this is more specifically for
server-sig-algsand RFC 8308 support.What version of Go are you using (
go version)?Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (
go env)?go envOutputWhat did you do?
Recently, OpenSSH 8.8 deprecated support for
ssh-rsahost keys andssh-rsapubkey auth as a default value. If users try to connect to a Gox/crypto/sshserver using OpenSSH 8.8 withssh-rsafor pubkey auth, the client will fail to find a mutual algorithm and not even attempt to send a client'sssh-rsapubkey auth, likely to avoid any auth penalties.What did you expect to see?
I would expect the SSH server to send an
SSH_MSG_EXT_INFOcontaining valid pubkey auth algorithms using theserver-sig-algsextension, as defined in RFC 8308.What did you see instead?
The
x/cryptoSSH server does not send any pubkey auth algorithms, so a client may end up not sending a potentially valid pubkey auth to avoid penalties.