Adding upstream version 0.0~git20250502.5100632.

Signed-off-by: Daniel Baumann <daniel@debian.org>

sign.go

@@ -0,0 +1,169 @@
+// Modifications by 42wim
+//
+// Copyright 2021 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sshsig
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/sha512"
+	"errors"
+	"hash"
+	"io"
+
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
+)
+
+// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L81
+type MessageWrapper struct {
+	Namespace     string
+	Reserved      string
+	HashAlgorithm string
+	Hash          string
+}
+
+// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L34
+type WrappedSig struct {
+	MagicHeader   [6]byte
+	Version       uint32
+	PublicKey     string
+	Namespace     string
+	Reserved      string
+	HashAlgorithm string
+	Signature     string
+}
+
+const (
+	magicHeader          = "SSHSIG"
+	defaultHashAlgorithm = "sha512"
+)
+
+var supportedHashAlgorithms = map[string]func() hash.Hash{
+	"sha256": sha256.New,
+	"sha512": sha512.New,
+}
+
+func wrapData(m io.Reader, ns string) ([]byte, error) {
+	hf := sha512.New()
+	if _, err := io.Copy(hf, m); err != nil {
+		return nil, err
+	}
+	mh := hf.Sum(nil)
+
+	sp := MessageWrapper{
+		Namespace:     ns,
+		HashAlgorithm: defaultHashAlgorithm,
+		Hash:          string(mh),
+	}
+
+	dataMessageWrapper := ssh.Marshal(sp)
+	dataMessageWrapper = append([]byte(magicHeader), dataMessageWrapper...)
+
+	return dataMessageWrapper, nil
+}
+
+func sign(s ssh.AlgorithmSigner, m io.Reader, ns string) (*ssh.Signature, error) {
+	dataMessageWrapper, err := wrapData(m, ns)
+	if err != nil {
+		return nil, err
+	}
+	// ssh-rsa is not supported for RSA keys:
+	// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L71
+	// We can use the default value of "" for other key types though.
+	algo := ""
+	if s.PublicKey().Type() == ssh.KeyAlgoRSA {
+		algo = ssh.SigAlgoRSASHA2512
+	}
+
+	return s.SignWithAlgorithm(rand.Reader, dataMessageWrapper, algo)
+}
+
+func signAgent(pk ssh.PublicKey, ag agent.Agent, m io.Reader, ns string) (*ssh.Signature, error) {
+	dataMessageWrapper, err := wrapData(m, ns)
+	if err != nil {
+		return nil, err
+	}
+
+	var sigFlag agent.SignatureFlags
+	if pk.Type() == ssh.KeyAlgoRSA {
+		sigFlag = agent.SignatureFlagRsaSha512
+	}
+
+	agExt, ok := ag.(agent.ExtendedAgent)
+	if !ok {
+		return nil, errors.New("couldn't cast to ExtendedAgent")
+	}
+
+	return agExt.SignWithFlags(pk, dataMessageWrapper, sigFlag)
+}
+
+// SignWithAgent asks the ssh Agent to sign the data with the signer matching the given publicKey and returns an armored signature.
+// The purpose of the namespace value is to specify a unambiguous
+// interpretation domain for the signature, e.g. file signing.
+// This prevents cross-protocol attacks caused by signatures
+// intended for one intended domain being accepted in another.
+// If empty, the default is "file".
+// This can be compared with `ssh-keygen -Y sign -f keyfile -n namespace data`
+func SignWithAgent(publicKey []byte, ag agent.Agent, data io.Reader, namespace string) ([]byte, error) {
+	pk, _, _, _, err := ssh.ParseAuthorizedKey(publicKey)
+	if err != nil {
+		return nil, err
+	}
+
+	if namespace == "" {
+		namespace = defaultNamespace
+	}
+
+	sig, err := signAgent(pk, ag, data, namespace)
+	if err != nil {
+		return nil, err
+	}
+
+	armored := Armor(sig, pk, namespace)
+	return armored, nil
+}
+
+// Sign signs the data with the given private key in PEM format and returns an armored signature.
+// The purpose of the namespace value is to specify a unambiguous
+// interpretation domain for the signature, e.g. file signing.
+// This prevents cross-protocol attacks caused by signatures
+// intended for one intended domain being accepted in another.
+// If empty, the default is "file".
+// This can be compared with `ssh-keygen -Y sign -f keyfile -n namespace data`
+func Sign(pemBytes []byte, data io.Reader, namespace string) ([]byte, error) {
+	s, err := ssh.ParsePrivateKey(pemBytes)
+	if err != nil {
+		return nil, err
+	}
+
+	as, ok := s.(ssh.AlgorithmSigner)
+	if !ok {
+		return nil, err
+	}
+
+	if namespace == "" {
+		namespace = defaultNamespace
+	}
+
+	sig, err := sign(as, data, namespace)
+	if err != nil {
+		return nil, err
+	}
+
+	armored := Armor(sig, s.PublicKey(), namespace)
+	return armored, nil
+}