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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package agent
import (
"crypto/dsa"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rsa"
"encoding/binary"
"errors"
"fmt"
"io"
"log"
"math/big"
"golang.org/x/crypto/ed25519"
"golang.org/x/crypto/ssh"
)
// Server wraps an Agent and uses it to implement the agent side of
// the SSH-agent, wire protocol.
type server struct {
agent Agent
}
func (s *server) processRequestBytes(reqData []byte) []byte {
rep, err := s.processRequest(reqData)
if err != nil {
if err != errLocked {
// TODO(hanwen): provide better logging interface?
log.Printf("agent %d: %v", reqData[0], err)
}
return []byte{agentFailure}
}
if err == nil && rep == nil {
return []byte{agentSuccess}
}
return ssh.Marshal(rep)
}
func marshalKey(k *Key) []byte {
var record struct {
Blob []byte
Comment string
}
record.Blob = k.Marshal()
record.Comment = k.Comment
return ssh.Marshal(&record)
}
// See [PROTOCOL.agent], section 2.5.1.
const agentV1IdentitiesAnswer = 2
type agentV1IdentityMsg struct {
Numkeys uint32 `sshtype:"2"`
}
type agentRemoveIdentityMsg struct {
KeyBlob []byte `sshtype:"18"`
}
type agentLockMsg struct {
Passphrase []byte `sshtype:"22"`
}
type agentUnlockMsg struct {
Passphrase []byte `sshtype:"23"`
}
func (s *server) processRequest(data []byte) (interface{}, error) {
switch data[0] {
case agentRequestV1Identities:
return &agentV1IdentityMsg{0}, nil
case agentRemoveAllV1Identities:
return nil, nil
case agentRemoveIdentity:
var req agentRemoveIdentityMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
var wk wireKey
if err := ssh.Unmarshal(req.KeyBlob, &wk); err != nil {
return nil, err
}
return nil, s.agent.Remove(&Key{Format: wk.Format, Blob: req.KeyBlob})
case agentRemoveAllIdentities:
return nil, s.agent.RemoveAll()
case agentLock:
var req agentLockMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
return nil, s.agent.Lock(req.Passphrase)
case agentUnlock:
var req agentUnlockMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
return nil, s.agent.Unlock(req.Passphrase)
case agentSignRequest:
var req signRequestAgentMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
var wk wireKey
if err := ssh.Unmarshal(req.KeyBlob, &wk); err != nil {
return nil, err
}
k := &Key{
Format: wk.Format,
Blob: req.KeyBlob,
}
var sig *ssh.Signature
var err error
if extendedAgent, ok := s.agent.(ExtendedAgent); ok {
sig, err = extendedAgent.SignWithFlags(k, req.Data, SignatureFlags(req.Flags))
} else {
sig, err = s.agent.Sign(k, req.Data)
}
if err != nil {
return nil, err
}
return &signResponseAgentMsg{SigBlob: ssh.Marshal(sig)}, nil
case agentRequestIdentities:
keys, err := s.agent.List()
if err != nil {
return nil, err
}
rep := identitiesAnswerAgentMsg{
NumKeys: uint32(len(keys)),
}
for _, k := range keys {
rep.Keys = append(rep.Keys, marshalKey(k)...)
}
return rep, nil
case agentAddIDConstrained, agentAddIdentity:
return nil, s.insertIdentity(data)
case agentExtension:
// Return a stub object where the whole contents of the response gets marshaled.
var responseStub struct {
Rest []byte `ssh:"rest"`
}
if extendedAgent, ok := s.agent.(ExtendedAgent); !ok {
// If this agent doesn't implement extensions, [PROTOCOL.agent] section 4.7
// requires that we return a standard SSH_AGENT_FAILURE message.
responseStub.Rest = []byte{agentFailure}
} else {
var req extensionAgentMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
res, err := extendedAgent.Extension(req.ExtensionType, req.Contents)
if err != nil {
// If agent extensions are unsupported, return a standard SSH_AGENT_FAILURE
// message as required by [PROTOCOL.agent] section 4.7.
if err == ErrExtensionUnsupported {
responseStub.Rest = []byte{agentFailure}
} else {
// As the result of any other error processing an extension request,
// [PROTOCOL.agent] section 4.7 requires that we return a
// SSH_AGENT_EXTENSION_FAILURE code.
responseStub.Rest = []byte{agentExtensionFailure}
}
} else {
if len(res) == 0 {
return nil, nil
}
responseStub.Rest = res
}
}
return responseStub, nil
}
return nil, fmt.Errorf("unknown opcode %d", data[0])
}
func parseConstraints(constraints []byte) (lifetimeSecs uint32, confirmBeforeUse bool, extensions []ConstraintExtension, err error) {
for len(constraints) != 0 {
switch constraints[0] {
case agentConstrainLifetime:
lifetimeSecs = binary.BigEndian.Uint32(constraints[1:5])
constraints = constraints[5:]
case agentConstrainConfirm:
confirmBeforeUse = true
constraints = constraints[1:]
case agentConstrainExtension:
var msg constrainExtensionAgentMsg
if err = ssh.Unmarshal(constraints, &msg); err != nil {
return 0, false, nil, err
}
extensions = append(extensions, ConstraintExtension{
ExtensionName: msg.ExtensionName,
ExtensionDetails: msg.ExtensionDetails,
})
constraints = msg.Rest
default:
return 0, false, nil, fmt.Errorf("unknown constraint type: %d", constraints[0])
}
}
return
}
func setConstraints(key *AddedKey, constraintBytes []byte) error {
lifetimeSecs, confirmBeforeUse, constraintExtensions, err := parseConstraints(constraintBytes)
if err != nil {
return err
}
key.LifetimeSecs = lifetimeSecs
key.ConfirmBeforeUse = confirmBeforeUse
key.ConstraintExtensions = constraintExtensions
return nil
}
func parseRSAKey(req []byte) (*AddedKey, error) {
var k rsaKeyMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
if k.E.BitLen() > 30 {
return nil, errors.New("agent: RSA public exponent too large")
}
priv := &rsa.PrivateKey{
PublicKey: rsa.PublicKey{
E: int(k.E.Int64()),
N: k.N,
},
D: k.D,
Primes: []*big.Int{k.P, k.Q},
}
priv.Precompute()
addedKey := &AddedKey{PrivateKey: priv, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseEd25519Key(req []byte) (*AddedKey, error) {
var k ed25519KeyMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
priv := ed25519.PrivateKey(k.Priv)
addedKey := &AddedKey{PrivateKey: &priv, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseDSAKey(req []byte) (*AddedKey, error) {
var k dsaKeyMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
priv := &dsa.PrivateKey{
PublicKey: dsa.PublicKey{
Parameters: dsa.Parameters{
P: k.P,
Q: k.Q,
G: k.G,
},
Y: k.Y,
},
X: k.X,
}
addedKey := &AddedKey{PrivateKey: priv, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func unmarshalECDSA(curveName string, keyBytes []byte, privScalar *big.Int) (priv *ecdsa.PrivateKey, err error) {
priv = &ecdsa.PrivateKey{
D: privScalar,
}
switch curveName {
case "nistp256":
priv.Curve = elliptic.P256()
case "nistp384":
priv.Curve = elliptic.P384()
case "nistp521":
priv.Curve = elliptic.P521()
default:
return nil, fmt.Errorf("agent: unknown curve %q", curveName)
}
priv.X, priv.Y = elliptic.Unmarshal(priv.Curve, keyBytes)
if priv.X == nil || priv.Y == nil {
return nil, errors.New("agent: point not on curve")
}
return priv, nil
}
func parseEd25519Cert(req []byte) (*AddedKey, error) {
var k ed25519CertMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
pubKey, err := ssh.ParsePublicKey(k.CertBytes)
if err != nil {
return nil, err
}
priv := ed25519.PrivateKey(k.Priv)
cert, ok := pubKey.(*ssh.Certificate)
if !ok {
return nil, errors.New("agent: bad ED25519 certificate")
}
addedKey := &AddedKey{PrivateKey: &priv, Certificate: cert, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseECDSAKey(req []byte) (*AddedKey, error) {
var k ecdsaKeyMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
priv, err := unmarshalECDSA(k.Curve, k.KeyBytes, k.D)
if err != nil {
return nil, err
}
addedKey := &AddedKey{PrivateKey: priv, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseRSACert(req []byte) (*AddedKey, error) {
var k rsaCertMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
pubKey, err := ssh.ParsePublicKey(k.CertBytes)
if err != nil {
return nil, err
}
cert, ok := pubKey.(*ssh.Certificate)
if !ok {
return nil, errors.New("agent: bad RSA certificate")
}
// An RSA publickey as marshaled by rsaPublicKey.Marshal() in keys.go
var rsaPub struct {
Name string
E *big.Int
N *big.Int
}
if err := ssh.Unmarshal(cert.Key.Marshal(), &rsaPub); err != nil {
return nil, fmt.Errorf("agent: Unmarshal failed to parse public key: %v", err)
}
if rsaPub.E.BitLen() > 30 {
return nil, errors.New("agent: RSA public exponent too large")
}
priv := rsa.PrivateKey{
PublicKey: rsa.PublicKey{
E: int(rsaPub.E.Int64()),
N: rsaPub.N,
},
D: k.D,
Primes: []*big.Int{k.Q, k.P},
}
priv.Precompute()
addedKey := &AddedKey{PrivateKey: &priv, Certificate: cert, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseDSACert(req []byte) (*AddedKey, error) {
var k dsaCertMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
pubKey, err := ssh.ParsePublicKey(k.CertBytes)
if err != nil {
return nil, err
}
cert, ok := pubKey.(*ssh.Certificate)
if !ok {
return nil, errors.New("agent: bad DSA certificate")
}
// A DSA publickey as marshaled by dsaPublicKey.Marshal() in keys.go
var w struct {
Name string
P, Q, G, Y *big.Int
}
if err := ssh.Unmarshal(cert.Key.Marshal(), &w); err != nil {
return nil, fmt.Errorf("agent: Unmarshal failed to parse public key: %v", err)
}
priv := &dsa.PrivateKey{
PublicKey: dsa.PublicKey{
Parameters: dsa.Parameters{
P: w.P,
Q: w.Q,
G: w.G,
},
Y: w.Y,
},
X: k.X,
}
addedKey := &AddedKey{PrivateKey: priv, Certificate: cert, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func parseECDSACert(req []byte) (*AddedKey, error) {
var k ecdsaCertMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
pubKey, err := ssh.ParsePublicKey(k.CertBytes)
if err != nil {
return nil, err
}
cert, ok := pubKey.(*ssh.Certificate)
if !ok {
return nil, errors.New("agent: bad ECDSA certificate")
}
// An ECDSA publickey as marshaled by ecdsaPublicKey.Marshal() in keys.go
var ecdsaPub struct {
Name string
ID string
Key []byte
}
if err := ssh.Unmarshal(cert.Key.Marshal(), &ecdsaPub); err != nil {
return nil, err
}
priv, err := unmarshalECDSA(ecdsaPub.ID, ecdsaPub.Key, k.D)
if err != nil {
return nil, err
}
addedKey := &AddedKey{PrivateKey: priv, Certificate: cert, Comment: k.Comments}
if err := setConstraints(addedKey, k.Constraints); err != nil {
return nil, err
}
return addedKey, nil
}
func (s *server) insertIdentity(req []byte) error {
var record struct {
Type string `sshtype:"17|25"`
Rest []byte `ssh:"rest"`
}
if err := ssh.Unmarshal(req, &record); err != nil {
return err
}
var addedKey *AddedKey
var err error
switch record.Type {
case ssh.KeyAlgoRSA:
addedKey, err = parseRSAKey(req)
case ssh.KeyAlgoDSA:
addedKey, err = parseDSAKey(req)
case ssh.KeyAlgoECDSA256, ssh.KeyAlgoECDSA384, ssh.KeyAlgoECDSA521:
addedKey, err = parseECDSAKey(req)
case ssh.KeyAlgoED25519:
addedKey, err = parseEd25519Key(req)
case ssh.CertAlgoRSAv01:
addedKey, err = parseRSACert(req)
case ssh.CertAlgoDSAv01:
addedKey, err = parseDSACert(req)
case ssh.CertAlgoECDSA256v01, ssh.CertAlgoECDSA384v01, ssh.CertAlgoECDSA521v01:
addedKey, err = parseECDSACert(req)
case ssh.CertAlgoED25519v01:
addedKey, err = parseEd25519Cert(req)
default:
return fmt.Errorf("agent: not implemented: %q", record.Type)
}
if err != nil {
return err
}
return s.agent.Add(*addedKey)
}
// ServeAgent serves the agent protocol on the given connection. It
// returns when an I/O error occurs.
func ServeAgent(agent Agent, c io.ReadWriter) error {
s := &server{agent}
var length [4]byte
for {
if _, err := io.ReadFull(c, length[:]); err != nil {
return err
}
l := binary.BigEndian.Uint32(length[:])
if l == 0 {
return fmt.Errorf("agent: request size is 0")
}
if l > maxAgentResponseBytes {
// We also cap requests.
return fmt.Errorf("agent: request too large: %d", l)
}
req := make([]byte, l)
if _, err := io.ReadFull(c, req); err != nil {
return err
}
repData := s.processRequestBytes(req)
if len(repData) > maxAgentResponseBytes {
return fmt.Errorf("agent: reply too large: %d bytes", len(repData))
}
binary.BigEndian.PutUint32(length[:], uint32(len(repData)))
if _, err := c.Write(length[:]); err != nil {
return err
}
if _, err := c.Write(repData); err != nil {
return err
}
}
}