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