mirror of
https://github.com/go-gitea/gitea.git
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790 lines
21 KiB
Go
790 lines
21 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package agent implements the ssh-agent protocol, and provides both
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// a client and a server. The client can talk to a standard ssh-agent
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// that uses UNIX sockets, and one could implement an alternative
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// ssh-agent process using the sample server.
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//
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// References:
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// [PROTOCOL.agent]: https://tools.ietf.org/html/draft-miller-ssh-agent-00
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package agent // import "golang.org/x/crypto/ssh/agent"
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import (
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"bytes"
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"crypto/dsa"
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"crypto/ecdsa"
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"crypto/elliptic"
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"crypto/rsa"
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"encoding/base64"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"math/big"
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"sync"
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"crypto"
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"golang.org/x/crypto/ed25519"
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"golang.org/x/crypto/ssh"
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)
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// SignatureFlags represent additional flags that can be passed to the signature
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// requests an defined in [PROTOCOL.agent] section 4.5.1.
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type SignatureFlags uint32
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// SignatureFlag values as defined in [PROTOCOL.agent] section 5.3.
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const (
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SignatureFlagReserved SignatureFlags = 1 << iota
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SignatureFlagRsaSha256
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SignatureFlagRsaSha512
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)
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// Agent represents the capabilities of an ssh-agent.
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type Agent interface {
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// List returns the identities known to the agent.
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List() ([]*Key, error)
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// Sign has the agent sign the data using a protocol 2 key as defined
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// in [PROTOCOL.agent] section 2.6.2.
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Sign(key ssh.PublicKey, data []byte) (*ssh.Signature, error)
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// Add adds a private key to the agent.
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Add(key AddedKey) error
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// Remove removes all identities with the given public key.
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Remove(key ssh.PublicKey) error
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// RemoveAll removes all identities.
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RemoveAll() error
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// Lock locks the agent. Sign and Remove will fail, and List will empty an empty list.
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Lock(passphrase []byte) error
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// Unlock undoes the effect of Lock
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Unlock(passphrase []byte) error
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// Signers returns signers for all the known keys.
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Signers() ([]ssh.Signer, error)
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}
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type ExtendedAgent interface {
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Agent
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// SignWithFlags signs like Sign, but allows for additional flags to be sent/received
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SignWithFlags(key ssh.PublicKey, data []byte, flags SignatureFlags) (*ssh.Signature, error)
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// Extension processes a custom extension request. Standard-compliant agents are not
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// required to support any extensions, but this method allows agents to implement
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// vendor-specific methods or add experimental features. See [PROTOCOL.agent] section 4.7.
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// If agent extensions are unsupported entirely this method MUST return an
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// ErrExtensionUnsupported error. Similarly, if just the specific extensionType in
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// the request is unsupported by the agent then ErrExtensionUnsupported MUST be
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// returned.
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//
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// In the case of success, since [PROTOCOL.agent] section 4.7 specifies that the contents
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// of the response are unspecified (including the type of the message), the complete
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// response will be returned as a []byte slice, including the "type" byte of the message.
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Extension(extensionType string, contents []byte) ([]byte, error)
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}
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// ConstraintExtension describes an optional constraint defined by users.
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type ConstraintExtension struct {
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// ExtensionName consist of a UTF-8 string suffixed by the
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// implementation domain following the naming scheme defined
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// in Section 4.2 of [RFC4251], e.g. "foo@example.com".
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ExtensionName string
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// ExtensionDetails contains the actual content of the extended
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// constraint.
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ExtensionDetails []byte
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}
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// AddedKey describes an SSH key to be added to an Agent.
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type AddedKey struct {
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// PrivateKey must be a *rsa.PrivateKey, *dsa.PrivateKey or
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// *ecdsa.PrivateKey, which will be inserted into the agent.
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PrivateKey interface{}
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// Certificate, if not nil, is communicated to the agent and will be
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// stored with the key.
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Certificate *ssh.Certificate
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// Comment is an optional, free-form string.
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Comment string
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// LifetimeSecs, if not zero, is the number of seconds that the
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// agent will store the key for.
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LifetimeSecs uint32
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// ConfirmBeforeUse, if true, requests that the agent confirm with the
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// user before each use of this key.
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ConfirmBeforeUse bool
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// ConstraintExtensions are the experimental or private-use constraints
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// defined by users.
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ConstraintExtensions []ConstraintExtension
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}
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// See [PROTOCOL.agent], section 3.
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const (
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agentRequestV1Identities = 1
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agentRemoveAllV1Identities = 9
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// 3.2 Requests from client to agent for protocol 2 key operations
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agentAddIdentity = 17
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agentRemoveIdentity = 18
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agentRemoveAllIdentities = 19
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agentAddIDConstrained = 25
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// 3.3 Key-type independent requests from client to agent
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agentAddSmartcardKey = 20
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agentRemoveSmartcardKey = 21
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agentLock = 22
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agentUnlock = 23
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agentAddSmartcardKeyConstrained = 26
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// 3.7 Key constraint identifiers
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agentConstrainLifetime = 1
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agentConstrainConfirm = 2
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agentConstrainExtension = 3
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)
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// maxAgentResponseBytes is the maximum agent reply size that is accepted. This
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// is a sanity check, not a limit in the spec.
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const maxAgentResponseBytes = 16 << 20
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// Agent messages:
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// These structures mirror the wire format of the corresponding ssh agent
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// messages found in [PROTOCOL.agent].
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// 3.4 Generic replies from agent to client
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const agentFailure = 5
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type failureAgentMsg struct{}
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const agentSuccess = 6
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type successAgentMsg struct{}
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// See [PROTOCOL.agent], section 2.5.2.
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const agentRequestIdentities = 11
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type requestIdentitiesAgentMsg struct{}
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// See [PROTOCOL.agent], section 2.5.2.
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const agentIdentitiesAnswer = 12
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type identitiesAnswerAgentMsg struct {
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NumKeys uint32 `sshtype:"12"`
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Keys []byte `ssh:"rest"`
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}
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// See [PROTOCOL.agent], section 2.6.2.
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const agentSignRequest = 13
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type signRequestAgentMsg struct {
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KeyBlob []byte `sshtype:"13"`
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Data []byte
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Flags uint32
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}
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// See [PROTOCOL.agent], section 2.6.2.
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// 3.6 Replies from agent to client for protocol 2 key operations
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const agentSignResponse = 14
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type signResponseAgentMsg struct {
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SigBlob []byte `sshtype:"14"`
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}
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type publicKey struct {
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Format string
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Rest []byte `ssh:"rest"`
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}
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// 3.7 Key constraint identifiers
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type constrainLifetimeAgentMsg struct {
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LifetimeSecs uint32 `sshtype:"1"`
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}
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type constrainExtensionAgentMsg struct {
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ExtensionName string `sshtype:"3"`
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ExtensionDetails []byte
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// Rest is a field used for parsing, not part of message
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Rest []byte `ssh:"rest"`
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}
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// See [PROTOCOL.agent], section 4.7
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const agentExtension = 27
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const agentExtensionFailure = 28
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// ErrExtensionUnsupported indicates that an extension defined in
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// [PROTOCOL.agent] section 4.7 is unsupported by the agent. Specifically this
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// error indicates that the agent returned a standard SSH_AGENT_FAILURE message
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// as the result of a SSH_AGENTC_EXTENSION request. Note that the protocol
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// specification (and therefore this error) does not distinguish between a
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// specific extension being unsupported and extensions being unsupported entirely.
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var ErrExtensionUnsupported = errors.New("agent: extension unsupported")
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type extensionAgentMsg struct {
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ExtensionType string `sshtype:"27"`
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Contents []byte
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}
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// Key represents a protocol 2 public key as defined in
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// [PROTOCOL.agent], section 2.5.2.
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type Key struct {
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Format string
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Blob []byte
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Comment string
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}
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func clientErr(err error) error {
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return fmt.Errorf("agent: client error: %v", err)
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}
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// String returns the storage form of an agent key with the format, base64
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// encoded serialized key, and the comment if it is not empty.
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func (k *Key) String() string {
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s := string(k.Format) + " " + base64.StdEncoding.EncodeToString(k.Blob)
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if k.Comment != "" {
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s += " " + k.Comment
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}
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return s
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}
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// Type returns the public key type.
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func (k *Key) Type() string {
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return k.Format
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}
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// Marshal returns key blob to satisfy the ssh.PublicKey interface.
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func (k *Key) Marshal() []byte {
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return k.Blob
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}
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// Verify satisfies the ssh.PublicKey interface.
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func (k *Key) Verify(data []byte, sig *ssh.Signature) error {
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pubKey, err := ssh.ParsePublicKey(k.Blob)
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if err != nil {
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return fmt.Errorf("agent: bad public key: %v", err)
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}
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return pubKey.Verify(data, sig)
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}
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type wireKey struct {
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Format string
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Rest []byte `ssh:"rest"`
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}
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func parseKey(in []byte) (out *Key, rest []byte, err error) {
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var record struct {
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Blob []byte
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Comment string
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Rest []byte `ssh:"rest"`
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}
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if err := ssh.Unmarshal(in, &record); err != nil {
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return nil, nil, err
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}
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var wk wireKey
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if err := ssh.Unmarshal(record.Blob, &wk); err != nil {
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return nil, nil, err
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}
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return &Key{
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Format: wk.Format,
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Blob: record.Blob,
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Comment: record.Comment,
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}, record.Rest, nil
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}
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// client is a client for an ssh-agent process.
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type client struct {
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// conn is typically a *net.UnixConn
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conn io.ReadWriter
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// mu is used to prevent concurrent access to the agent
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mu sync.Mutex
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}
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// NewClient returns an Agent that talks to an ssh-agent process over
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// the given connection.
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func NewClient(rw io.ReadWriter) ExtendedAgent {
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return &client{conn: rw}
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}
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// call sends an RPC to the agent. On success, the reply is
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// unmarshaled into reply and replyType is set to the first byte of
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// the reply, which contains the type of the message.
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func (c *client) call(req []byte) (reply interface{}, err error) {
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buf, err := c.callRaw(req)
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if err != nil {
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return nil, err
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}
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reply, err = unmarshal(buf)
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if err != nil {
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return nil, clientErr(err)
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}
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return reply, nil
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}
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// callRaw sends an RPC to the agent. On success, the raw
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// bytes of the response are returned; no unmarshalling is
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// performed on the response.
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func (c *client) callRaw(req []byte) (reply []byte, err error) {
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c.mu.Lock()
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defer c.mu.Unlock()
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msg := make([]byte, 4+len(req))
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binary.BigEndian.PutUint32(msg, uint32(len(req)))
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copy(msg[4:], req)
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if _, err = c.conn.Write(msg); err != nil {
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return nil, clientErr(err)
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}
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var respSizeBuf [4]byte
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if _, err = io.ReadFull(c.conn, respSizeBuf[:]); err != nil {
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return nil, clientErr(err)
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}
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respSize := binary.BigEndian.Uint32(respSizeBuf[:])
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if respSize > maxAgentResponseBytes {
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return nil, clientErr(errors.New("response too large"))
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}
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buf := make([]byte, respSize)
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if _, err = io.ReadFull(c.conn, buf); err != nil {
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return nil, clientErr(err)
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}
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return buf, nil
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}
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func (c *client) simpleCall(req []byte) error {
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resp, err := c.call(req)
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if err != nil {
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return err
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}
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if _, ok := resp.(*successAgentMsg); ok {
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return nil
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}
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return errors.New("agent: failure")
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}
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func (c *client) RemoveAll() error {
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return c.simpleCall([]byte{agentRemoveAllIdentities})
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}
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func (c *client) Remove(key ssh.PublicKey) error {
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req := ssh.Marshal(&agentRemoveIdentityMsg{
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KeyBlob: key.Marshal(),
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})
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return c.simpleCall(req)
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}
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func (c *client) Lock(passphrase []byte) error {
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req := ssh.Marshal(&agentLockMsg{
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Passphrase: passphrase,
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})
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return c.simpleCall(req)
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}
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func (c *client) Unlock(passphrase []byte) error {
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req := ssh.Marshal(&agentUnlockMsg{
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Passphrase: passphrase,
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})
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return c.simpleCall(req)
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}
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// List returns the identities known to the agent.
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func (c *client) List() ([]*Key, error) {
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// see [PROTOCOL.agent] section 2.5.2.
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req := []byte{agentRequestIdentities}
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msg, err := c.call(req)
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if err != nil {
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return nil, err
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}
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switch msg := msg.(type) {
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case *identitiesAnswerAgentMsg:
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if msg.NumKeys > maxAgentResponseBytes/8 {
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return nil, errors.New("agent: too many keys in agent reply")
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}
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keys := make([]*Key, msg.NumKeys)
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data := msg.Keys
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for i := uint32(0); i < msg.NumKeys; i++ {
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var key *Key
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var err error
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if key, data, err = parseKey(data); err != nil {
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return nil, err
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}
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keys[i] = key
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}
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return keys, nil
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case *failureAgentMsg:
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return nil, errors.New("agent: failed to list keys")
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}
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panic("unreachable")
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}
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// Sign has the agent sign the data using a protocol 2 key as defined
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// in [PROTOCOL.agent] section 2.6.2.
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func (c *client) Sign(key ssh.PublicKey, data []byte) (*ssh.Signature, error) {
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return c.SignWithFlags(key, data, 0)
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}
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func (c *client) SignWithFlags(key ssh.PublicKey, data []byte, flags SignatureFlags) (*ssh.Signature, error) {
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req := ssh.Marshal(signRequestAgentMsg{
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KeyBlob: key.Marshal(),
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Data: data,
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Flags: uint32(flags),
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})
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msg, err := c.call(req)
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if err != nil {
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return nil, err
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}
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switch msg := msg.(type) {
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case *signResponseAgentMsg:
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var sig ssh.Signature
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if err := ssh.Unmarshal(msg.SigBlob, &sig); err != nil {
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return nil, err
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}
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return &sig, nil
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case *failureAgentMsg:
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return nil, errors.New("agent: failed to sign challenge")
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}
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panic("unreachable")
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}
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// unmarshal parses an agent message in packet, returning the parsed
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// form and the message type of packet.
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func unmarshal(packet []byte) (interface{}, error) {
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if len(packet) < 1 {
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return nil, errors.New("agent: empty packet")
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}
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var msg interface{}
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switch packet[0] {
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case agentFailure:
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return new(failureAgentMsg), nil
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case agentSuccess:
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return new(successAgentMsg), nil
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case agentIdentitiesAnswer:
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msg = new(identitiesAnswerAgentMsg)
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case agentSignResponse:
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msg = new(signResponseAgentMsg)
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case agentV1IdentitiesAnswer:
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msg = new(agentV1IdentityMsg)
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default:
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return nil, fmt.Errorf("agent: unknown type tag %d", packet[0])
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}
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if err := ssh.Unmarshal(packet, msg); err != nil {
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return nil, err
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}
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return msg, nil
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}
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type rsaKeyMsg struct {
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Type string `sshtype:"17|25"`
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N *big.Int
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E *big.Int
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D *big.Int
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Iqmp *big.Int // IQMP = Inverse Q Mod P
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P *big.Int
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Q *big.Int
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Comments string
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Constraints []byte `ssh:"rest"`
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}
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type dsaKeyMsg struct {
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Type string `sshtype:"17|25"`
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P *big.Int
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Q *big.Int
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G *big.Int
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Y *big.Int
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X *big.Int
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Comments string
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Constraints []byte `ssh:"rest"`
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}
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type ecdsaKeyMsg struct {
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Type string `sshtype:"17|25"`
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Curve string
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KeyBytes []byte
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D *big.Int
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Comments string
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Constraints []byte `ssh:"rest"`
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}
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type ed25519KeyMsg struct {
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Type string `sshtype:"17|25"`
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Pub []byte
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Priv []byte
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Comments string
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Constraints []byte `ssh:"rest"`
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}
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// Insert adds a private key to the agent.
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func (c *client) insertKey(s interface{}, comment string, constraints []byte) error {
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var req []byte
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switch k := s.(type) {
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case *rsa.PrivateKey:
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if len(k.Primes) != 2 {
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return fmt.Errorf("agent: unsupported RSA key with %d primes", len(k.Primes))
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}
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k.Precompute()
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req = ssh.Marshal(rsaKeyMsg{
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Type: ssh.KeyAlgoRSA,
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N: k.N,
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E: big.NewInt(int64(k.E)),
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D: k.D,
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Iqmp: k.Precomputed.Qinv,
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P: k.Primes[0],
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Q: k.Primes[1],
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Comments: comment,
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Constraints: constraints,
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})
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case *dsa.PrivateKey:
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req = ssh.Marshal(dsaKeyMsg{
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Type: ssh.KeyAlgoDSA,
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P: k.P,
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Q: k.Q,
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G: k.G,
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Y: k.Y,
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X: k.X,
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Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
case *ecdsa.PrivateKey:
|
|
nistID := fmt.Sprintf("nistp%d", k.Params().BitSize)
|
|
req = ssh.Marshal(ecdsaKeyMsg{
|
|
Type: "ecdsa-sha2-" + nistID,
|
|
Curve: nistID,
|
|
KeyBytes: elliptic.Marshal(k.Curve, k.X, k.Y),
|
|
D: k.D,
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
case *ed25519.PrivateKey:
|
|
req = ssh.Marshal(ed25519KeyMsg{
|
|
Type: ssh.KeyAlgoED25519,
|
|
Pub: []byte(*k)[32:],
|
|
Priv: []byte(*k),
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
default:
|
|
return fmt.Errorf("agent: unsupported key type %T", s)
|
|
}
|
|
|
|
// if constraints are present then the message type needs to be changed.
|
|
if len(constraints) != 0 {
|
|
req[0] = agentAddIDConstrained
|
|
}
|
|
|
|
resp, err := c.call(req)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if _, ok := resp.(*successAgentMsg); ok {
|
|
return nil
|
|
}
|
|
return errors.New("agent: failure")
|
|
}
|
|
|
|
type rsaCertMsg struct {
|
|
Type string `sshtype:"17|25"`
|
|
CertBytes []byte
|
|
D *big.Int
|
|
Iqmp *big.Int // IQMP = Inverse Q Mod P
|
|
P *big.Int
|
|
Q *big.Int
|
|
Comments string
|
|
Constraints []byte `ssh:"rest"`
|
|
}
|
|
|
|
type dsaCertMsg struct {
|
|
Type string `sshtype:"17|25"`
|
|
CertBytes []byte
|
|
X *big.Int
|
|
Comments string
|
|
Constraints []byte `ssh:"rest"`
|
|
}
|
|
|
|
type ecdsaCertMsg struct {
|
|
Type string `sshtype:"17|25"`
|
|
CertBytes []byte
|
|
D *big.Int
|
|
Comments string
|
|
Constraints []byte `ssh:"rest"`
|
|
}
|
|
|
|
type ed25519CertMsg struct {
|
|
Type string `sshtype:"17|25"`
|
|
CertBytes []byte
|
|
Pub []byte
|
|
Priv []byte
|
|
Comments string
|
|
Constraints []byte `ssh:"rest"`
|
|
}
|
|
|
|
// Add adds a private key to the agent. If a certificate is given,
|
|
// that certificate is added instead as public key.
|
|
func (c *client) Add(key AddedKey) error {
|
|
var constraints []byte
|
|
|
|
if secs := key.LifetimeSecs; secs != 0 {
|
|
constraints = append(constraints, ssh.Marshal(constrainLifetimeAgentMsg{secs})...)
|
|
}
|
|
|
|
if key.ConfirmBeforeUse {
|
|
constraints = append(constraints, agentConstrainConfirm)
|
|
}
|
|
|
|
cert := key.Certificate
|
|
if cert == nil {
|
|
return c.insertKey(key.PrivateKey, key.Comment, constraints)
|
|
}
|
|
return c.insertCert(key.PrivateKey, cert, key.Comment, constraints)
|
|
}
|
|
|
|
func (c *client) insertCert(s interface{}, cert *ssh.Certificate, comment string, constraints []byte) error {
|
|
var req []byte
|
|
switch k := s.(type) {
|
|
case *rsa.PrivateKey:
|
|
if len(k.Primes) != 2 {
|
|
return fmt.Errorf("agent: unsupported RSA key with %d primes", len(k.Primes))
|
|
}
|
|
k.Precompute()
|
|
req = ssh.Marshal(rsaCertMsg{
|
|
Type: cert.Type(),
|
|
CertBytes: cert.Marshal(),
|
|
D: k.D,
|
|
Iqmp: k.Precomputed.Qinv,
|
|
P: k.Primes[0],
|
|
Q: k.Primes[1],
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
case *dsa.PrivateKey:
|
|
req = ssh.Marshal(dsaCertMsg{
|
|
Type: cert.Type(),
|
|
CertBytes: cert.Marshal(),
|
|
X: k.X,
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
case *ecdsa.PrivateKey:
|
|
req = ssh.Marshal(ecdsaCertMsg{
|
|
Type: cert.Type(),
|
|
CertBytes: cert.Marshal(),
|
|
D: k.D,
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
case *ed25519.PrivateKey:
|
|
req = ssh.Marshal(ed25519CertMsg{
|
|
Type: cert.Type(),
|
|
CertBytes: cert.Marshal(),
|
|
Pub: []byte(*k)[32:],
|
|
Priv: []byte(*k),
|
|
Comments: comment,
|
|
Constraints: constraints,
|
|
})
|
|
default:
|
|
return fmt.Errorf("agent: unsupported key type %T", s)
|
|
}
|
|
|
|
// if constraints are present then the message type needs to be changed.
|
|
if len(constraints) != 0 {
|
|
req[0] = agentAddIDConstrained
|
|
}
|
|
|
|
signer, err := ssh.NewSignerFromKey(s)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if bytes.Compare(cert.Key.Marshal(), signer.PublicKey().Marshal()) != 0 {
|
|
return errors.New("agent: signer and cert have different public key")
|
|
}
|
|
|
|
resp, err := c.call(req)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if _, ok := resp.(*successAgentMsg); ok {
|
|
return nil
|
|
}
|
|
return errors.New("agent: failure")
|
|
}
|
|
|
|
// Signers provides a callback for client authentication.
|
|
func (c *client) Signers() ([]ssh.Signer, error) {
|
|
keys, err := c.List()
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
var result []ssh.Signer
|
|
for _, k := range keys {
|
|
result = append(result, &agentKeyringSigner{c, k})
|
|
}
|
|
return result, nil
|
|
}
|
|
|
|
type agentKeyringSigner struct {
|
|
agent *client
|
|
pub ssh.PublicKey
|
|
}
|
|
|
|
func (s *agentKeyringSigner) PublicKey() ssh.PublicKey {
|
|
return s.pub
|
|
}
|
|
|
|
func (s *agentKeyringSigner) Sign(rand io.Reader, data []byte) (*ssh.Signature, error) {
|
|
// The agent has its own entropy source, so the rand argument is ignored.
|
|
return s.agent.Sign(s.pub, data)
|
|
}
|
|
|
|
func (s *agentKeyringSigner) SignWithOpts(rand io.Reader, data []byte, opts crypto.SignerOpts) (*ssh.Signature, error) {
|
|
var flags SignatureFlags
|
|
if opts != nil {
|
|
switch opts.HashFunc() {
|
|
case crypto.SHA256:
|
|
flags = SignatureFlagRsaSha256
|
|
case crypto.SHA512:
|
|
flags = SignatureFlagRsaSha512
|
|
}
|
|
}
|
|
return s.agent.SignWithFlags(s.pub, data, flags)
|
|
}
|
|
|
|
// Calls an extension method. It is up to the agent implementation as to whether or not
|
|
// any particular extension is supported and may always return an error. Because the
|
|
// type of the response is up to the implementation, this returns the bytes of the
|
|
// response and does not attempt any type of unmarshalling.
|
|
func (c *client) Extension(extensionType string, contents []byte) ([]byte, error) {
|
|
req := ssh.Marshal(extensionAgentMsg{
|
|
ExtensionType: extensionType,
|
|
Contents: contents,
|
|
})
|
|
buf, err := c.callRaw(req)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
if len(buf) == 0 {
|
|
return nil, errors.New("agent: failure; empty response")
|
|
}
|
|
// [PROTOCOL.agent] section 4.7 indicates that an SSH_AGENT_FAILURE message
|
|
// represents an agent that does not support the extension
|
|
if buf[0] == agentFailure {
|
|
return nil, ErrExtensionUnsupported
|
|
}
|
|
if buf[0] == agentExtensionFailure {
|
|
return nil, errors.New("agent: generic extension failure")
|
|
}
|
|
|
|
return buf, nil
|
|
}
|