x/crypto/openpgp: ReadEntity doesn't support V3 signatures

[emersion]

What version of Go are you using (go version)?

1.11

Does this issue reproduce with the latest release?

Aye.

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/simon/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/simon/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build609952039=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Try to use openpgp.ReadEntity on a keyring containing V3 signatures (for instance http://keyserver.mattrude.com/dump/current/sks-dump-0000.pgp).

package main

import (
	"io"
	"log"
	"os"

	"golang.org/x/crypto/openpgp"
	"golang.org/x/crypto/openpgp/packet"
)

func main() {
	pr := packet.NewReader(os.Stdin)
	for {
		_, err := openpgp.ReadEntity(pr)
		if err == io.EOF {
			break
		} else if err != nil {
			log.Fatal(err)
		}
	}
}

What did you expect to see?

No error.

What did you see instead?

openpgp: invalid data: subkey packet not followed by signature

This happens because of this line: https://github.com/golang/crypto/blob/master/openpgp/keys.go#L442

• We should at least provide a sensible error message if it's a *packet.SignatureV3 ("V3 signatures not supported by Entity").
• We could add a SignatureV3 field alongside Signature fields (just like MessageDetails)

What do you think?

[FiloSottile]

Per the accepted #44226 proposal and due to lack of maintenance, the golang.org/x/crypto/openpgp package is now frozen and deprecated. No new changes will be accepted except for security fixes. The package will not be removed.

If this is a security issue, please email security@golang.org and we will assess it and provide a fix.

If you're looking for alternatives, consider the crypto/ed25519 package for simple signatures, golang.org/x/mod/sumdb/note for inline signatures, or filippo.io/age for encryption. You can read a summary of OpenPGP issues and alternatives here.

If you are required to interoperate with OpenPGP systems and need a maintained package, we suggest considering one of multiple community forks of golang.org/x/crypto/openpgp. We don't endorse any specific one.