615 lines
15 KiB
Go
Executable file
615 lines
15 KiB
Go
Executable file
// 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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/*
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Package agent implements a client to an ssh-agent daemon.
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References:
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[PROTOCOL.agent]: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.agent?rev=HEAD
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*/
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package 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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"github.com/gogits/gogs/modules/crypto/ssh"
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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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// 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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}
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// See [PROTOCOL.agent], section 3.
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const (
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agentRequestV1Identities = 1
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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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)
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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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// 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, but is not
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// implemented for agent keys.
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func (k *Key) Verify(data []byte, sig *ssh.Signature) error {
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return errors.New("agent: agent key does not know how to verify")
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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) Agent {
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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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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(err)
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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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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, err
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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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req := ssh.Marshal(signRequestAgentMsg{
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KeyBlob: key.Marshal(),
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Data: data,
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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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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"`
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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"`
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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"`
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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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// 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,
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Constraints: constraints,
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})
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case *ecdsa.PrivateKey:
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nistID := fmt.Sprintf("nistp%d", k.Params().BitSize)
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req = ssh.Marshal(ecdsaKeyMsg{
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Type: "ecdsa-sha2-" + nistID,
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Curve: nistID,
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KeyBytes: elliptic.Marshal(k.Curve, k.X, k.Y),
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D: k.D,
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Comments: comment,
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Constraints: constraints,
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})
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default:
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return fmt.Errorf("agent: unsupported key type %T", s)
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}
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// if constraints are present then the message type needs to be changed.
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if len(constraints) != 0 {
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req[0] = agentAddIdConstrained
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}
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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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type rsaCertMsg struct {
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Type string `sshtype:"17"`
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CertBytes []byte
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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 dsaCertMsg struct {
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Type string `sshtype:"17"`
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CertBytes []byte
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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 ecdsaCertMsg struct {
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Type string `sshtype:"17"`
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CertBytes []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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// Insert adds a private key to the agent. If a certificate is given,
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// that certificate is added instead as public key.
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func (c *client) Add(key AddedKey) error {
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var constraints []byte
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if secs := key.LifetimeSecs; secs != 0 {
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constraints = append(constraints, agentConstrainLifetime)
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var secsBytes [4]byte
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binary.BigEndian.PutUint32(secsBytes[:], secs)
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constraints = append(constraints, secsBytes[:]...)
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}
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if key.ConfirmBeforeUse {
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constraints = append(constraints, agentConstrainConfirm)
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}
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if cert := key.Certificate; cert == nil {
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return c.insertKey(key.PrivateKey, key.Comment, constraints)
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} else {
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return c.insertCert(key.PrivateKey, cert, key.Comment, constraints)
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}
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}
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func (c *client) insertCert(s interface{}, cert *ssh.Certificate, 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(rsaCertMsg{
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Type: cert.Type(),
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CertBytes: cert.Marshal(),
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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(dsaCertMsg{
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Type: cert.Type(),
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CertBytes: cert.Marshal(),
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X: k.X,
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Comments: comment,
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})
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case *ecdsa.PrivateKey:
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req = ssh.Marshal(ecdsaCertMsg{
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Type: cert.Type(),
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CertBytes: cert.Marshal(),
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D: k.D,
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Comments: comment,
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})
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default:
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return fmt.Errorf("agent: unsupported key type %T", s)
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}
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// if constraints are present then the message type needs to be changed.
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if len(constraints) != 0 {
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req[0] = agentAddIdConstrained
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}
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signer, err := ssh.NewSignerFromKey(s)
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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)
|
|
}
|