ssh

package
v2.0.16+incompatible Latest Latest
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This package is not in the latest version of its module.

 Go to latest Published: Sep 15, 2021 License: GPL-3.0, BSD-3-Clause Imports: 47 Imported by: 60

Documentation

Overview

Package ssh implements an SSH client and server.

SSH is a transport security protocol, an authentication protocol and a family of application protocols. The most typical application level protocol is a remote shell and this is specifically implemented. However, the multiplexed nature of SSH is exposed to users that wish to support others.

References: 

[PROTOCOL.certkeys]: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.certkeys?rev=HEAD
[SSH-PARAMETERS]:    http://www.iana.org/assignments/ssh-parameters/ssh-parameters.xml#ssh-parameters-1

This package does not fall under the stability promise of the Go language itself, so its API may be changed when pressing needs arise.

Index

Examples

Constants

View Source 
const (
	CertAlgoRSAv01      = "ssh-rsa-cert-v01@openssh.com"
	CertAlgoDSAv01      = "ssh-dss-cert-v01@openssh.com"
	CertAlgoECDSA256v01 = "ecdsa-sha2-nistp256-cert-v01@openssh.com"
	CertAlgoECDSA384v01 = "ecdsa-sha2-nistp384-cert-v01@openssh.com"
	CertAlgoECDSA521v01 = "ecdsa-sha2-nistp521-cert-v01@openssh.com"
	CertAlgoED25519v01  = "ssh-ed25519-cert-v01@openssh.com"
)

These constants from [PROTOCOL.certkeys] represent the algorithm names for certificate types supported by this package.

View Source 
const (
	UserCert = 1
	HostCert = 2
)

Certificate types distinguish between host and user certificates. The values can be set in the CertType field of Certificate.

View Source 
const (
	KeyAlgoRSA      = "ssh-rsa"
	KeyAlgoDSA      = "ssh-dss"
	KeyAlgoECDSA256 = "ecdsa-sha2-nistp256"
	KeyAlgoECDSA384 = "ecdsa-sha2-nistp384"
	KeyAlgoECDSA521 = "ecdsa-sha2-nistp521"
	KeyAlgoED25519  = "ssh-ed25519"
)

These constants represent the algorithm names for key types supported by this package.

View Source 
const (
	VINTR         = 1
	VQUIT         = 2
	VERASE        = 3
	VKILL         = 4
	VEOF          = 5
	VEOL          = 6
	VEOL2         = 7
	VSTART        = 8
	VSTOP         = 9
	VSUSP         = 10
	VDSUSP        = 11
	VREPRINT      = 12
	VWERASE       = 13
	VLNEXT        = 14
	VFLUSH        = 15
	VSWTCH        = 16
	VSTATUS       = 17
	VDISCARD      = 18
	IGNPAR        = 30
	PARMRK        = 31
	INPCK         = 32
	ISTRIP        = 33
	INLCR         = 34
	IGNCR         = 35
	ICRNL         = 36
	IUCLC         = 37
	IXON          = 38
	IXANY         = 39
	IXOFF         = 40
	IMAXBEL       = 41
	ISIG          = 50
	ICANON        = 51
	XCASE         = 52
	ECHO          = 53
	ECHOE         = 54
	ECHOK         = 55
	ECHONL        = 56
	NOFLSH        = 57
	TOSTOP        = 58
	IEXTEN        = 59
	ECHOCTL       = 60
	ECHOKE        = 61
	PENDIN        = 62
	OPOST         = 70
	OLCUC         = 71
	ONLCR         = 72
	OCRNL         = 73
	ONOCR         = 74
	ONLRET        = 75
	CS7           = 90
	CS8           = 91
	PARENB        = 92
	PARODD        = 93
	TTY_OP_ISPEED = 128
	TTY_OP_OSPEED = 129
)

POSIX terminal mode flags as listed in RFC 4254 Section 8.

View Source 
const CertTimeInfinity = 1<<64 - 1

CertTimeInfinity can be used for OpenSSHCertV01.ValidBefore to indicate that a certificate does not expire.

Variables

View Source 
var ErrNoAuth = errors.New("ssh: no auth passed yet")

ErrNoAuth is the error value returned if no authentication method has been passed yet. This happens as a normal part of the authentication loop, since the client first tries 'none' authentication to discover available methods. It is returned in ServerAuthError.Errors from NewServerConn.

Functions

func DiscardRequests 

func DiscardRequests(in <-chan *Request)

DiscardRequests consumes and rejects all requests from the passed-in channel.

func FingerprintLegacyMD5 

func FingerprintLegacyMD5(pubKey PublicKey) string

FingerprintLegacyMD5 returns the user presentation of the key's fingerprint as described by RFC 4716 section 4.

func FingerprintSHA256 

func FingerprintSHA256(pubKey PublicKey) string

FingerprintSHA256 returns the user presentation of the key's fingerprint as unpadded base64 encoded sha256 hash. This format was introduced from OpenSSH 6.8. https://www.openssh.com/txt/release-6.8 https://tools.ietf.org/html/rfc4648#section-3.2 (unpadded base64 encoding)

func Marshal 

func Marshal(msg interface{}) []byte

Marshal serializes the message in msg to SSH wire format. The msg argument should be a struct or pointer to struct. If the first member has the "sshtype" tag set to a number in decimal, that number is prepended to the result. If the last of member has the "ssh" tag set to "rest", its contents are appended to the output.

func MarshalAuthorizedKey 

func MarshalAuthorizedKey(key PublicKey) []byte

MarshalAuthorizedKey serializes key for inclusion in an OpenSSH authorized_keys file. The return value ends with newline.

func ParseDSAPrivateKey 

func ParseDSAPrivateKey(der []byte) (*dsa.PrivateKey, error)

ParseDSAPrivateKey returns a DSA private key from its ASN.1 DER encoding, as specified by the OpenSSL DSA man page.

func ParseRawPrivateKey 

func ParseRawPrivateKey(pemBytes []byte) (interface{}, error)

ParseRawPrivateKey returns a private key from a PEM encoded private key. It supports RSA (PKCS#1), PKCS#8, DSA (OpenSSL), and ECDSA private keys.

func ParseRawPrivateKeyWithPassphrase 

func ParseRawPrivateKeyWithPassphrase(pemBytes, passPhrase []byte) (interface{}, error)

ParseRawPrivateKeyWithPassphrase returns a private key decrypted with passphrase from a PEM encoded private key. If wrong passphrase, return x509.IncorrectPasswordError.

func Unmarshal 

func Unmarshal(data []byte, out interface{}) error

Unmarshal parses data in SSH wire format into a structure. The out argument should be a pointer to struct. If the first member of the struct has the "sshtype" tag set to a '|'-separated set of numbers in decimal, the packet must start with one of those numbers. In case of error, Unmarshal returns a ParseError or UnexpectedMessageError.

Types

type AuthMethod 

type AuthMethod interface {
	// contains filtered or unexported methods
}

An AuthMethod represents an instance of an RFC 4252 authentication method.

func KeyboardInteractive 

func KeyboardInteractive(challenge KeyboardInteractiveChallenge) AuthMethod

KeyboardInteractive returns an AuthMethod using a prompt/response sequence controlled by the server.

func Password 

func Password(secret string) AuthMethod

Password returns an AuthMethod using the given password.

func PasswordCallback 

func PasswordCallback(prompt func() (secret string, err error)) AuthMethod

PasswordCallback returns an AuthMethod that uses a callback for fetching a password.

func PublicKeys 

func PublicKeys(signers ...Signer) AuthMethod

PublicKeys returns an AuthMethod that uses the given key pairs.

Example 
package main

import (
	"io/ioutil"
	"log"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
)

func main() {
	var hostKey ssh.PublicKey
	// A public key may be used to authenticate against the remote
	// server by using an unencrypted PEM-encoded private key file.
	//
	// If you have an encrypted private key, the crypto/x509 package
	// can be used to decrypt it.
	key, err := ioutil.ReadFile("/home/user/.ssh/id_rsa")
	if err != nil {
		log.Fatalf("unable to read private key: %v", err)
	}

	// Create the Signer for this private key.
	signer, err := ssh.ParsePrivateKey(key)
	if err != nil {
		log.Fatalf("unable to parse private key: %v", err)
	}

	config := &ssh.ClientConfig{
		User: "user",
		Auth: []ssh.AuthMethod{
			// Use the PublicKeys method for remote authentication.
			ssh.PublicKeys(signer),
		},
		HostKeyCallback: ssh.FixedHostKey(hostKey),
	}

	// Connect to the remote server and perform the SSH handshake.
	client, err := ssh.Dial("tcp", "host.com:22", config)
	if err != nil {
		log.Fatalf("unable to connect: %v", err)
	}
	defer client.Close()
}

Output:

func PublicKeysCallback 

func PublicKeysCallback(getSigners func() (signers []Signer, err error)) AuthMethod

PublicKeysCallback returns an AuthMethod that runs the given function to obtain a list of key pairs.

func RetryableAuthMethod 

func RetryableAuthMethod(auth AuthMethod, maxTries int) AuthMethod

RetryableAuthMethod is a decorator for other auth methods enabling them to be retried up to maxTries before considering that AuthMethod itself failed. If maxTries is <= 0, will retry indefinitely

This is useful for interactive clients using challenge/response type authentication (e.g. Keyboard-Interactive, Password, etc) where the user could mistype their response resulting in the server issuing a SSH_MSG_USERAUTH_FAILURE (rfc4252 #8 [password] and rfc4256 #3.4 [keyboard-interactive]); Without this decorator, the non-retryable AuthMethod would be removed from future consideration, and never tried again (and so the user would never be able to retry their entry).

type BannerCallback added in v1.0.9 

type BannerCallback func(message string) error

BannerCallback is the function type used for treat the banner sent by the server. A BannerCallback receives the message sent by the remote server.

func BannerDisplayStderr added in v1.0.9 

func BannerDisplayStderr() BannerCallback

BannerDisplayStderr returns a function that can be used for ClientConfig.BannerCallback to display banners on os.Stderr.

type CertChecker 

type CertChecker struct {
	// SupportedCriticalOptions lists the CriticalOptions that the
	// server application layer understands. These are only used
	// for user certificates.
	SupportedCriticalOptions []string

	// IsUserAuthority should return true if the key is recognized as an
	// authority for the given user certificate. This allows for
	// certificates to be signed by other certificates. This must be set
	// if this CertChecker will be checking user certificates.
	IsUserAuthority func(auth PublicKey) bool

	// IsHostAuthority should report whether the key is recognized as
	// an authority for this host. This allows for certificates to be
	// signed by other keys, and for those other keys to only be valid
	// signers for particular hostnames. This must be set if this
	// CertChecker will be checking host certificates.
	IsHostAuthority func(auth PublicKey, address string) bool

	// Clock is used for verifying time stamps. If nil, time.Now
	// is used.
	Clock func() time.Time

	// UserKeyFallback is called when CertChecker.Authenticate encounters a
	// public key that is not a certificate. It must implement validation
	// of user keys or else, if nil, all such keys are rejected.
	UserKeyFallback func(conn ConnMetadata, key PublicKey) (*Permissions, error)

	// HostKeyFallback is called when CertChecker.CheckHostKey encounters a
	// public key that is not a certificate. It must implement host key
	// validation or else, if nil, all such keys are rejected.
	HostKeyFallback HostKeyCallback

	// IsRevoked is called for each certificate so that revocation checking
	// can be implemented. It should return true if the given certificate
	// is revoked and false otherwise. If nil, no certificates are
	// considered to have been revoked.
	IsRevoked func(cert *Certificate) bool
}

CertChecker does the work of verifying a certificate. Its methods can be plugged into ClientConfig.HostKeyCallback and ServerConfig.PublicKeyCallback. For the CertChecker to work, minimally, the IsAuthority callback should be set.

func (*CertChecker) Authenticate 

func (c *CertChecker) Authenticate(conn ConnMetadata, pubKey PublicKey) (*Permissions, error)

Authenticate checks a user certificate. Authenticate can be used as a value for ServerConfig.PublicKeyCallback.

func (*CertChecker) CheckCert 

func (c *CertChecker) CheckCert(principal string, cert *Certificate) error

CheckCert checks CriticalOptions, ValidPrincipals, revocation, timestamp and the signature of the certificate.

func (*CertChecker) CheckHostKey 

func (c *CertChecker) CheckHostKey(addr string, remote net.Addr, key PublicKey) error

CheckHostKey checks a host key certificate. This method can be plugged into ClientConfig.HostKeyCallback.

type Certificate 

type Certificate struct {
	Nonce           []byte
	Key             PublicKey
	Serial          uint64
	CertType        uint32
	KeyId           string
	ValidPrincipals []string
	ValidAfter      uint64
	ValidBefore     uint64
	Permissions
	Reserved     []byte
	SignatureKey PublicKey
	Signature    *Signature
}

An Certificate represents an OpenSSH certificate as defined in [PROTOCOL.certkeys]?rev=1.8. The Certificate type implements the PublicKey interface, so it can be unmarshaled using ParsePublicKey.

func (*Certificate) Marshal 

func (c *Certificate) Marshal() []byte

Marshal serializes c into OpenSSH's wire format. It is part of the PublicKey interface.

func (*Certificate) SignCert 

func (c *Certificate) SignCert(rand io.Reader, authority Signer) error

SignCert sets c.SignatureKey to the authority's public key and stores a Signature, by authority, in the certificate.

func (*Certificate) Type 

func (c *Certificate) Type() string

Type returns the key name. It is part of the PublicKey interface.

func (*Certificate) Verify 

func (c *Certificate) Verify(data []byte, sig *Signature) error

Verify verifies a signature against the certificate's public key. It is part of the PublicKey interface.

type Channel 

type Channel interface {
	// Read reads up to len(data) bytes from the channel.
	Read(data []byte) (int, error)

	// Write writes len(data) bytes to the channel.
	Write(data []byte) (int, error)

	// Close signals end of channel use. No data may be sent after this
	// call.
	Close() error

	// CloseWrite signals the end of sending in-band
	// data. Requests may still be sent, and the other side may
	// still send data
	CloseWrite() error

	// SendRequest sends a channel request.  If wantReply is true,
	// it will wait for a reply and return the result as a
	// boolean, otherwise the return value will be false. Channel
	// requests are out-of-band messages so they may be sent even
	// if the data stream is closed or blocked by flow control.
	// If the channel is closed before a reply is returned, io.EOF
	// is returned.
	SendRequest(name string, wantReply bool, payload []byte) (bool, error)

	// Stderr returns an io.ReadWriter that writes to this channel
	// with the extended data type set to stderr. Stderr may
	// safely be read and written from a different goroutine than
	// Read and Write respectively.
	Stderr() io.ReadWriter
}

A Channel is an ordered, reliable, flow-controlled, duplex stream that is multiplexed over an SSH connection.

type Client 

type Client struct {
	Conn
	// contains filtered or unexported fields
}

Client implements a traditional SSH client that supports shells, subprocesses, TCP port/streamlocal forwarding and tunneled dialing.

func Dial 

func Dial(network, addr string, config *ClientConfig) (*Client, error)

Dial starts a client connection to the given SSH server. It is a convenience function that connects to the given network address, initiates the SSH handshake, and then sets up a Client. For access to incoming channels and requests, use net.Dial with NewClientConn instead.

Example 
package main

import (
	"bytes"
	"fmt"
	"log"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
)

func main() {
	var hostKey ssh.PublicKey
	// An SSH client is represented with a ClientConn.
	//
	// To authenticate with the remote server you must pass at least one
	// implementation of AuthMethod via the Auth field in ClientConfig,
	// and provide a HostKeyCallback.
	config := &ssh.ClientConfig{
		User: "username",
		Auth: []ssh.AuthMethod{
			ssh.Password("yourpassword"),
		},
		HostKeyCallback: ssh.FixedHostKey(hostKey),
	}
	client, err := ssh.Dial("tcp", "yourserver.com:22", config)
	if err != nil {
		log.Fatal("Failed to dial: ", err)
	}

	// Each ClientConn can support multiple interactive sessions,
	// represented by a Session.
	session, err := client.NewSession()
	if err != nil {
		log.Fatal("Failed to create session: ", err)
	}
	defer session.Close()

	// Once a Session is created, you can execute a single command on
	// the remote side using the Run method.
	var b bytes.Buffer
	session.Stdout = &b
	if err := session.Run("/usr/bin/whoami"); err != nil {
		log.Fatal("Failed to run: " + err.Error())
	}
	fmt.Println(b.String())
}

Output:

func NewClient 

func NewClient(c Conn, chans <-chan NewChannel, reqs <-chan *Request) *Client

NewClient creates a Client on top of the given connection.

func (*Client) Dial 

func (c *Client) Dial(n, addr string) (net.Conn, error)

Dial initiates a connection to the addr from the remote host. The resulting connection has a zero LocalAddr() and RemoteAddr().

func (*Client) DialTCP 

func (c *Client) DialTCP(n string, laddr, raddr *net.TCPAddr) (net.Conn, error)

DialTCP connects to the remote address raddr on the network net, which must be "tcp", "tcp4", or "tcp6". If laddr is not nil, it is used as the local address for the connection.

func (*Client) HandleChannelOpen 

func (c *Client) HandleChannelOpen(channelType string) <-chan NewChannel

HandleChannelOpen returns a channel on which NewChannel requests for the given type are sent. If the type already is being handled, nil is returned. The channel is closed when the connection is closed.

func (*Client) Listen 

func (c *Client) Listen(n, addr string) (net.Listener, error)

Listen requests the remote peer open a listening socket on addr. Incoming connections will be available by calling Accept on the returned net.Listener. The listener must be serviced, or the SSH connection may hang. N must be "tcp", "tcp4", "tcp6", or "unix".

Example 
package main

import (
	"fmt"
	"log"
	"net/http"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
)

func main() {
	var hostKey ssh.PublicKey
	config := &ssh.ClientConfig{
		User: "username",
		Auth: []ssh.AuthMethod{
			ssh.Password("password"),
		},
		HostKeyCallback: ssh.FixedHostKey(hostKey),
	}
	// Dial your ssh server.
	conn, err := ssh.Dial("tcp", "localhost:22", config)
	if err != nil {
		log.Fatal("unable to connect: ", err)
	}
	defer conn.Close()

	// Request the remote side to open port 8080 on all interfaces.
	l, err := conn.Listen("tcp", "0.0.0.0:8080")
	if err != nil {
		log.Fatal("unable to register tcp forward: ", err)
	}
	defer l.Close()

	// Serve HTTP with your SSH server acting as a reverse proxy.
	http.Serve(l, http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
		fmt.Fprintf(resp, "Hello world!\n")
	}))
}

Output:

func (*Client) ListenTCP 

func (c *Client) ListenTCP(laddr *net.TCPAddr) (net.Listener, error)

ListenTCP requests the remote peer open a listening socket on laddr. Incoming connections will be available by calling Accept on the returned net.Listener.

func (*Client) ListenUnix 

func (c *Client) ListenUnix(socketPath string) (net.Listener, error)

ListenUnix is similar to ListenTCP but uses a Unix domain socket.

func (*Client) NewSession 

func (c *Client) NewSession() (*Session, error)

NewSession opens a new Session for this client. (A session is a remote execution of a program.)

type ClientConfig 

type ClientConfig struct {
	// Config contains configuration that is shared between clients and
	// servers.
	Config

	// User contains the username to authenticate as.
	User string

	// Auth contains possible authentication methods to use with the
	// server. Only the first instance of a particular RFC 4252 method will
	// be used during authentication.
	Auth []AuthMethod

	// HostKeyCallback is called during the cryptographic
	// handshake to validate the server's host key. The client
	// configuration must supply this callback for the connection
	// to succeed. The functions InsecureIgnoreHostKey or
	// FixedHostKey can be used for simplistic host key checks.
	HostKeyCallback HostKeyCallback

	// BannerCallback is called during the SSH dance to display a custom
	// server's message. The client configuration can supply this callback to
	// handle it as wished. The function BannerDisplayStderr can be used for
	// simplistic display on Stderr.
	BannerCallback BannerCallback

	// ClientVersion contains the version identification string that will
	// be used for the connection. If empty, a reasonable default is used.
	ClientVersion string

	// HostKeyAlgorithms lists the key types that the client will
	// accept from the server as host key, in order of
	// preference. If empty, a reasonable default is used. Any
	// string returned from PublicKey.Type method may be used, or
	// any of the CertAlgoXxxx and KeyAlgoXxxx constants.
	HostKeyAlgorithms []string

	// Timeout is the maximum amount of time for the TCP connection to establish.
	//
	// A Timeout of zero means no timeout.
	Timeout time.Duration
}

A ClientConfig structure is used to configure a Client. It must not be modified after having been passed to an SSH function.

type Config 

type Config struct {
	// Rand provides the source of entropy for cryptographic
	// primitives. If Rand is nil, the cryptographic random reader
	// in package crypto/rand will be used.
	Rand io.Reader

	// The maximum number of bytes sent or received after which a
	// new key is negotiated. It must be at least 256. If
	// unspecified, a size suitable for the chosen cipher is used.
	RekeyThreshold uint64

	// The allowed key exchanges algorithms. If unspecified then a
	// default set of algorithms is used.
	KeyExchanges []string

	// The allowed cipher algorithms. If unspecified then a sensible
	// default is used.
	Ciphers []string

	// The allowed MAC algorithms. If unspecified then a sensible default
	// is used.
	MACs []string

	// NoEncryptThenMACHash is used to disable Encrypt-then-MAC hash
	// algorithms.
	NoEncryptThenMACHash bool

	// KEXPRNGSeed is used for KEX randomization and replay.
	KEXPRNGSeed *prng.Seed

	// PeerKEXPRNGSeed is used to predict KEX randomization and make
	// adjustments to ensure negotiation succeeds.
	PeerKEXPRNGSeed *prng.Seed
}

Config contains configuration data common to both ServerConfig and ClientConfig.

func (*Config) SetDefaults 

func (c *Config) SetDefaults()

SetDefaults sets sensible values for unset fields in config. This is exported for testing: Configs passed to SSH functions are copied and have default values set automatically.

type Conn 

type Conn interface {
	ConnMetadata

	// SendRequest sends a global request, and returns the
	// reply. If wantReply is true, it returns the response status
	// and payload. See also RFC4254, section 4.
	SendRequest(name string, wantReply bool, payload []byte) (bool, []byte, error)

	// OpenChannel tries to open an channel. If the request is
	// rejected, it returns *OpenChannelError. On success it returns
	// the SSH Channel and a Go channel for incoming, out-of-band
	// requests. The Go channel must be serviced, or the
	// connection will hang.
	OpenChannel(name string, data []byte) (Channel, <-chan *Request, error)

	// Close closes the underlying network connection
	Close() error

	// Wait blocks until the connection has shut down, and returns the
	// error causing the shutdown.
	Wait() error
}

Conn represents an SSH connection for both server and client roles. Conn is the basis for implementing an application layer, such as ClientConn, which implements the traditional shell access for clients.

func NewClientConn 

func NewClientConn(c net.Conn, addr string, config *ClientConfig) (Conn, <-chan NewChannel, <-chan *Request, error)

NewClientConn establishes an authenticated SSH connection using c as the underlying transport. The Request and NewChannel channels must be serviced or the connection will hang.

type ConnMetadata 

type ConnMetadata interface {
	// User returns the user ID for this connection.
	User() string

	// SessionID returns the session hash, also denoted by H.
	SessionID() []byte

	// ClientVersion returns the client's version string as hashed
	// into the session ID.
	ClientVersion() []byte

	// ServerVersion returns the server's version string as hashed
	// into the session ID.
	ServerVersion() []byte

	// RemoteAddr returns the remote address for this connection.
	RemoteAddr() net.Addr

	// LocalAddr returns the local address for this connection.
	LocalAddr() net.Addr
}

ConnMetadata holds metadata for the connection.

type CryptoPublicKey 

type CryptoPublicKey interface {
	CryptoPublicKey() crypto.PublicKey
}

CryptoPublicKey, if implemented by a PublicKey, returns the underlying crypto.PublicKey form of the key.

type ExitError 

type ExitError struct {
	Waitmsg
}

An ExitError reports unsuccessful completion of a remote command.

func (*ExitError) Error 

func (e *ExitError) Error() string

type ExitMissingError 

type ExitMissingError struct{}

ExitMissingError is returned if a session is torn down cleanly, but the server sends no confirmation of the exit status.

func (*ExitMissingError) Error 

func (e *ExitMissingError) Error() string

type HostKeyCallback 

type HostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error

HostKeyCallback is the function type used for verifying server keys. A HostKeyCallback must return nil if the host key is OK, or an error to reject it. It receives the hostname as passed to Dial or NewClientConn. The remote address is the RemoteAddr of the net.Conn underlying the the SSH connection.

func FixedHostKey 

func FixedHostKey(key PublicKey) HostKeyCallback

FixedHostKey returns a function for use in ClientConfig.HostKeyCallback to accept only a specific host key.

func InsecureIgnoreHostKey 

func InsecureIgnoreHostKey() HostKeyCallback

InsecureIgnoreHostKey returns a function that can be used for ClientConfig.HostKeyCallback to accept any host key. It should not be used for production code.

type KeyboardInteractiveChallenge 

type KeyboardInteractiveChallenge func(user, instruction string, questions []string, echos []bool) (answers []string, err error)

KeyboardInteractiveChallenge should print questions, optionally disabling echoing (e.g. for passwords), and return all the answers. Challenge may be called multiple times in a single session. After successful authentication, the server may send a challenge with no questions, for which the user and instruction messages should be printed. RFC 4256 section 3.3 details how the UI should behave for both CLI and GUI environments.

type NewChannel 

type NewChannel interface {
	// Accept accepts the channel creation request. It returns the Channel
	// and a Go channel containing SSH requests. The Go channel must be
	// serviced otherwise the Channel will hang.
	Accept() (Channel, <-chan *Request, error)

	// Reject rejects the channel creation request. After calling
	// this, no other methods on the Channel may be called.
	Reject(reason RejectionReason, message string) error

	// ChannelType returns the type of the channel, as supplied by the
	// client.
	ChannelType() string

	// ExtraData returns the arbitrary payload for this channel, as supplied
	// by the client. This data is specific to the channel type.
	ExtraData() []byte
}

NewChannel represents an incoming request to a channel. It must either be accepted for use by calling Accept, or rejected by calling Reject.

type OpenChannelError 

type OpenChannelError struct {
	Reason  RejectionReason
	Message string
}

OpenChannelError is returned if the other side rejects an OpenChannel request.

func (*OpenChannelError) Error 

func (e *OpenChannelError) Error() string

type Permissions 

type Permissions struct {
	// CriticalOptions indicate restrictions to the default
	// permissions, and are typically used in conjunction with
	// user certificates. The standard for SSH certificates
	// defines "force-command" (only allow the given command to
	// execute) and "source-address" (only allow connections from
	// the given address). The SSH package currently only enforces
	// the "source-address" critical option. It is up to server
	// implementations to enforce other critical options, such as
	// "force-command", by checking them after the SSH handshake
	// is successful. In general, SSH servers should reject
	// connections that specify critical options that are unknown
	// or not supported.
	CriticalOptions map[string]string

	// Extensions are extra functionality that the server may
	// offer on authenticated connections. Lack of support for an
	// extension does not preclude authenticating a user. Common
	// extensions are "permit-agent-forwarding",
	// "permit-X11-forwarding". The Go SSH library currently does
	// not act on any extension, and it is up to server
	// implementations to honor them. Extensions can be used to
	// pass data from the authentication callbacks to the server
	// application layer.
	Extensions map[string]string
}

The Permissions type holds fine-grained permissions that are specific to a user or a specific authentication method for a user. The Permissions value for a successful authentication attempt is available in ServerConn, so it can be used to pass information from the user-authentication phase to the application layer.

type PublicKey 

type PublicKey interface {
	// Type returns the key's type, e.g. "ssh-rsa".
	Type() string

	// Marshal returns the serialized key data in SSH wire format,
	// with the name prefix. To unmarshal the returned data, use
	// the ParsePublicKey function.
	Marshal() []byte

	// Verify that sig is a signature on the given data using this
	// key. This function will hash the data appropriately first.
	Verify(data []byte, sig *Signature) error
}

PublicKey is an abstraction of different types of public keys.

func NewPublicKey 

func NewPublicKey(key interface{}) (PublicKey, error)

NewPublicKey takes an *rsa.PublicKey, *dsa.PublicKey, *ecdsa.PublicKey, or ed25519.PublicKey returns a corresponding PublicKey instance. ECDSA keys must use P-256, P-384 or P-521.

func ParseAuthorizedKey 

func ParseAuthorizedKey(in []byte) (out PublicKey, comment string, options []string, rest []byte, err error)

ParseAuthorizedKeys parses a public key from an authorized_keys file used in OpenSSH according to the sshd(8) manual page.

func ParseKnownHosts 

func ParseKnownHosts(in []byte) (marker string, hosts []string, pubKey PublicKey, comment string, rest []byte, err error)

ParseKnownHosts parses an entry in the format of the known_hosts file.

The known_hosts format is documented in the sshd(8) manual page. This function will parse a single entry from in. On successful return, marker will contain the optional marker value (i.e. "cert-authority" or "revoked") or else be empty, hosts will contain the hosts that this entry matches, pubKey will contain the public key and comment will contain any trailing comment at the end of the line. See the sshd(8) manual page for the various forms that a host string can take.

The unparsed remainder of the input will be returned in rest. This function can be called repeatedly to parse multiple entries.

If no entries were found in the input then err will be io.EOF. Otherwise a non-nil err value indicates a parse error.

func ParsePublicKey 

func ParsePublicKey(in []byte) (out PublicKey, err error)

ParsePublicKey parses an SSH public key formatted for use in the SSH wire protocol according to RFC 4253, section 6.6.

type RejectionReason 

type RejectionReason uint32

RejectionReason is an enumeration used when rejecting channel creation requests. See RFC 4254, section 5.1. 

const (
	Prohibited RejectionReason = iota + 1
	ConnectionFailed
	UnknownChannelType
	ResourceShortage
)

func (RejectionReason) String 

func (r RejectionReason) String() string

String converts the rejection reason to human readable form.

type Request 

type Request struct {
	Type      string
	WantReply bool
	Payload   []byte
	// contains filtered or unexported fields
}

Request is a request sent outside of the normal stream of data. Requests can either be specific to an SSH channel, or they can be global.

func (*Request) Reply 

func (r *Request) Reply(ok bool, payload []byte) error

Reply sends a response to a request. It must be called for all requests where WantReply is true and is a no-op otherwise. The payload argument is ignored for replies to channel-specific requests.

type ServerAuthError 

type ServerAuthError struct {
	// Errors contains authentication errors returned by the authentication
	// callback methods. The first entry is typically ErrNoAuth.
	Errors []error
}

ServerAuthError represents server authentication errors and is sometimes returned by NewServerConn. It appends any authentication errors that may occur, and is returned if all of the authentication methods provided by the user failed to authenticate.

func (ServerAuthError) Error 

func (l ServerAuthError) Error() string

type ServerConfig 

type ServerConfig struct {
	// Config contains configuration shared between client and server.
	Config

	// NoClientAuth is true if clients are allowed to connect without
	// authenticating.
	NoClientAuth bool

	// MaxAuthTries specifies the maximum number of authentication attempts
	// permitted per connection. If set to a negative number, the number of
	// attempts are unlimited. If set to zero, the number of attempts are limited
	// to 6.
	MaxAuthTries int

	// PasswordCallback, if non-nil, is called when a user
	// attempts to authenticate using a password.
	PasswordCallback func(conn ConnMetadata, password []byte) (*Permissions, error)

	// PublicKeyCallback, if non-nil, is called when a client
	// offers a public key for authentication. It must return a nil error
	// if the given public key can be used to authenticate the
	// given user. For example, see CertChecker.Authenticate. A
	// call to this function does not guarantee that the key
	// offered is in fact used to authenticate. To record any data
	// depending on the public key, store it inside a
	// Permissions.Extensions entry.
	PublicKeyCallback func(conn ConnMetadata, key PublicKey) (*Permissions, error)

	// KeyboardInteractiveCallback, if non-nil, is called when
	// keyboard-interactive authentication is selected (RFC
	// 4256). The client object's Challenge function should be
	// used to query the user. The callback may offer multiple
	// Challenge rounds. To avoid information leaks, the client
	// should be presented a challenge even if the user is
	// unknown.
	KeyboardInteractiveCallback func(conn ConnMetadata, client KeyboardInteractiveChallenge) (*Permissions, error)

	// AuthLogCallback, if non-nil, is called to log all authentication
	// attempts.
	AuthLogCallback func(conn ConnMetadata, method string, err error)

	// ServerVersion is the version identification string to announce in
	// the public handshake.
	// If empty, a reasonable default is used.
	// Note that RFC 4253 section 4.2 requires that this string start with
	// "SSH-2.0-".
	ServerVersion string

	// BannerCallback, if present, is called and the return string is sent to
	// the client after key exchange completed but before authentication.
	BannerCallback func(conn ConnMetadata) string
	// contains filtered or unexported fields
}

ServerConfig holds server specific configuration data.

func (*ServerConfig) AddHostKey 

func (s *ServerConfig) AddHostKey(key Signer)

AddHostKey adds a private key as a host key. If an existing host key exists with the same algorithm, it is overwritten. Each server config must have at least one host key.

type ServerConn 

type ServerConn struct {
	Conn

	// If the succeeding authentication callback returned a
	// non-nil Permissions pointer, it is stored here.
	Permissions *Permissions
}

ServerConn is an authenticated SSH connection, as seen from the server

func NewServerConn 

func NewServerConn(c net.Conn, config *ServerConfig) (*ServerConn, <-chan NewChannel, <-chan *Request, error)

NewServerConn starts a new SSH server with c as the underlying transport. It starts with a handshake and, if the handshake is unsuccessful, it closes the connection and returns an error. The Request and NewChannel channels must be serviced, or the connection will hang.

The returned error may be of type *ServerAuthError for authentication errors.

Example 
package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh/terminal"
)

func main() {
	// Public key authentication is done by comparing
	// the public key of a received connection
	// with the entries in the authorized_keys file.
	authorizedKeysBytes, err := ioutil.ReadFile("authorized_keys")
	if err != nil {
		log.Fatalf("Failed to load authorized_keys, err: %v", err)
	}

	authorizedKeysMap := map[string]bool{}
	for len(authorizedKeysBytes) > 0 {
		pubKey, _, _, rest, err := ssh.ParseAuthorizedKey(authorizedKeysBytes)
		if err != nil {
			log.Fatal(err)
		}

		authorizedKeysMap[string(pubKey.Marshal())] = true
		authorizedKeysBytes = rest
	}

	// An SSH server is represented by a ServerConfig, which holds
	// certificate details and handles authentication of ServerConns.
	config := &ssh.ServerConfig{
		// Remove to disable password auth.
		PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
			// Should use constant-time compare (or better, salt+hash) in
			// a production setting.
			if c.User() == "testuser" && string(pass) == "tiger" {
				return nil, nil
			}
			return nil, fmt.Errorf("password rejected for %q", c.User())
		},

		// Remove to disable public key auth.
		PublicKeyCallback: func(c ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
			if authorizedKeysMap[string(pubKey.Marshal())] {
				return &ssh.Permissions{
					// Record the public key used for authentication.
					Extensions: map[string]string{
						"pubkey-fp": ssh.FingerprintSHA256(pubKey),
					},
				}, nil
			}
			return nil, fmt.Errorf("unknown public key for %q", c.User())
		},
	}

	privateBytes, err := ioutil.ReadFile("id_rsa")
	if err != nil {
		log.Fatal("Failed to load private key: ", err)
	}

	private, err := ssh.ParsePrivateKey(privateBytes)
	if err != nil {
		log.Fatal("Failed to parse private key: ", err)
	}

	config.AddHostKey(private)

	// Once a ServerConfig has been configured, connections can be
	// accepted.
	listener, err := net.Listen("tcp", "0.0.0.0:2022")
	if err != nil {
		log.Fatal("failed to listen for connection: ", err)
	}
	nConn, err := listener.Accept()
	if err != nil {
		log.Fatal("failed to accept incoming connection: ", err)
	}

	// Before use, a handshake must be performed on the incoming
	// net.Conn.
	conn, chans, reqs, err := ssh.NewServerConn(nConn, config)
	if err != nil {
		log.Fatal("failed to handshake: ", err)
	}
	log.Printf("logged in with key %s", conn.Permissions.Extensions["pubkey-fp"])

	// The incoming Request channel must be serviced.
	go ssh.DiscardRequests(reqs)

	// Service the incoming Channel channel.
	for newChannel := range chans {
		// Channels have a type, depending on the application level
		// protocol intended. In the case of a shell, the type is
		// "session" and ServerShell may be used to present a simple
		// terminal interface.
		if newChannel.ChannelType() != "session" {
			newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
			continue
		}
		channel, requests, err := newChannel.Accept()
		if err != nil {
			log.Fatalf("Could not accept channel: %v", err)
		}

		// Sessions have out-of-band requests such as "shell",
		// "pty-req" and "env".  Here we handle only the
		// "shell" request.
		go func(in <-chan *ssh.Request) {
			for req := range in {
				req.Reply(req.Type == "shell", nil)
			}
		}(requests)

		term := terminal.NewTerminal(channel, "> ")

		go func() {
			defer channel.Close()
			for {
				line, err := term.ReadLine()
				if err != nil {
					break
				}
				fmt.Println(line)
			}
		}()
	}
}

Output:

type Session 

type Session struct {
	// Stdin specifies the remote process's standard input.
	// If Stdin is nil, the remote process reads from an empty
	// bytes.Buffer.
	Stdin io.Reader

	// Stdout and Stderr specify the remote process's standard
	// output and error.
	//
	// If either is nil, Run connects the corresponding file
	// descriptor to an instance of ioutil.Discard. There is a
	// fixed amount of buffering that is shared for the two streams.
	// If either blocks it may eventually cause the remote
	// command to block.
	Stdout io.Writer
	Stderr io.Writer
	// contains filtered or unexported fields
}

A Session represents a connection to a remote command or shell.

func (*Session) Close 

func (s *Session) Close() error

func (*Session) CombinedOutput 

func (s *Session) CombinedOutput(cmd string) ([]byte, error)

CombinedOutput runs cmd on the remote host and returns its combined standard output and standard error.

func (*Session) Output 

func (s *Session) Output(cmd string) ([]byte, error)

Output runs cmd on the remote host and returns its standard output.

func (*Session) RequestPty 

func (s *Session) RequestPty(term string, h, w int, termmodes TerminalModes) error

RequestPty requests the association of a pty with the session on the remote host.

Example 
package main

import (
	"log"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
)

func main() {
	var hostKey ssh.PublicKey
	// Create client config
	config := &ssh.ClientConfig{
		User: "username",
		Auth: []ssh.AuthMethod{
			ssh.Password("password"),
		},
		HostKeyCallback: ssh.FixedHostKey(hostKey),
	}
	// Connect to ssh server
	conn, err := ssh.Dial("tcp", "localhost:22", config)
	if err != nil {
		log.Fatal("unable to connect: ", err)
	}
	defer conn.Close()
	// Create a session
	session, err := conn.NewSession()
	if err != nil {
		log.Fatal("unable to create session: ", err)
	}
	defer session.Close()
	// Set up terminal modes
	modes := ssh.TerminalModes{
		ssh.ECHO:          0,     // disable echoing
		ssh.TTY_OP_ISPEED: 14400, // input speed = 14.4kbaud
		ssh.TTY_OP_OSPEED: 14400, // output speed = 14.4kbaud
	}
	// Request pseudo terminal
	if err := session.RequestPty("xterm", 40, 80, modes); err != nil {
		log.Fatal("request for pseudo terminal failed: ", err)
	}
	// Start remote shell
	if err := session.Shell(); err != nil {
		log.Fatal("failed to start shell: ", err)
	}
}

Output:

func (*Session) RequestSubsystem 

func (s *Session) RequestSubsystem(subsystem string) error

RequestSubsystem requests the association of a subsystem with the session on the remote host. A subsystem is a predefined command that runs in the background when the ssh session is initiated

func (*Session) Run 

func (s *Session) Run(cmd string) error

Run runs cmd on the remote host. Typically, the remote server passes cmd to the shell for interpretation. A Session only accepts one call to Run, Start, Shell, Output, or CombinedOutput.

The returned error is nil if the command runs, has no problems copying stdin, stdout, and stderr, and exits with a zero exit status.

If the remote server does not send an exit status, an error of type *ExitMissingError is returned. If the command completes unsuccessfully or is interrupted by a signal, the error is of type *ExitError. Other error types may be returned for I/O problems.

func (*Session) SendRequest 

func (s *Session) SendRequest(name string, wantReply bool, payload []byte) (bool, error)

SendRequest sends an out-of-band channel request on the SSH channel underlying the session.

func (*Session) Setenv 

func (s *Session) Setenv(name, value string) error

Setenv sets an environment variable that will be applied to any command executed by Shell or Run.

func (*Session) Shell 

func (s *Session) Shell() error

Shell starts a login shell on the remote host. A Session only accepts one call to Run, Start, Shell, Output, or CombinedOutput.

func (*Session) Signal 

func (s *Session) Signal(sig Signal) error

Signal sends the given signal to the remote process. sig is one of the SIG* constants.

func (*Session) Start 

func (s *Session) Start(cmd string) error

Start runs cmd on the remote host. Typically, the remote server passes cmd to the shell for interpretation. A Session only accepts one call to Run, Start or Shell.

func (*Session) StderrPipe 

func (s *Session) StderrPipe() (io.Reader, error)

StderrPipe returns a pipe that will be connected to the remote command's standard error when the command starts. There is a fixed amount of buffering that is shared between stdout and stderr streams. If the StderrPipe reader is not serviced fast enough it may eventually cause the remote command to block.

func (*Session) StdinPipe 

func (s *Session) StdinPipe() (io.WriteCloser, error)

StdinPipe returns a pipe that will be connected to the remote command's standard input when the command starts.

func (*Session) StdoutPipe 

func (s *Session) StdoutPipe() (io.Reader, error)

StdoutPipe returns a pipe that will be connected to the remote command's standard output when the command starts. There is a fixed amount of buffering that is shared between stdout and stderr streams. If the StdoutPipe reader is not serviced fast enough it may eventually cause the remote command to block.

func (*Session) Wait 

func (s *Session) Wait() error

Wait waits for the remote command to exit.

The returned error is nil if the command runs, has no problems copying stdin, stdout, and stderr, and exits with a zero exit status.

If the remote server does not send an exit status, an error of type *ExitMissingError is returned. If the command completes unsuccessfully or is interrupted by a signal, the error is of type *ExitError. Other error types may be returned for I/O problems.

func (*Session) WindowChange added in v1.0.9 

func (s *Session) WindowChange(h, w int) error

WindowChange informs the remote host about a terminal window dimension change to h rows and w columns.

type Signal 

type Signal string
const (
	SIGABRT Signal = "ABRT"
	SIGALRM Signal = "ALRM"
	SIGFPE  Signal = "FPE"
	SIGHUP  Signal = "HUP"
	SIGILL  Signal = "ILL"
	SIGINT  Signal = "INT"
	SIGKILL Signal = "KILL"
	SIGPIPE Signal = "PIPE"
	SIGQUIT Signal = "QUIT"
	SIGSEGV Signal = "SEGV"
	SIGTERM Signal = "TERM"
	SIGUSR1 Signal = "USR1"
	SIGUSR2 Signal = "USR2"
)

POSIX signals as listed in RFC 4254 Section 6.10.

type Signature 

type Signature struct {
	Format string
	Blob   []byte
}

Signature represents a cryptographic signature.

type Signer 

type Signer interface {
	// PublicKey returns an associated PublicKey instance.
	PublicKey() PublicKey

	// Sign returns raw signature for the given data. This method
	// will apply the hash specified for the keytype to the data.
	Sign(rand io.Reader, data []byte) (*Signature, error)
}

A Signer can create signatures that verify against a public key.

func NewCertSigner 

func NewCertSigner(cert *Certificate, signer Signer) (Signer, error)

NewCertSigner returns a Signer that signs with the given Certificate, whose private key is held by signer. It returns an error if the public key in cert doesn't match the key used by signer.

func NewSignerFromKey 

func NewSignerFromKey(key interface{}) (Signer, error)

NewSignerFromKey takes an *rsa.PrivateKey, *dsa.PrivateKey, *ecdsa.PrivateKey or any other crypto.Signer and returns a corresponding Signer instance. ECDSA keys must use P-256, P-384 or P-521. DSA keys must use parameter size L1024N160.

func NewSignerFromSigner 

func NewSignerFromSigner(signer crypto.Signer) (Signer, error)

NewSignerFromSigner takes any crypto.Signer implementation and returns a corresponding Signer interface. This can be used, for example, with keys kept in hardware modules.

func ParsePrivateKey 

func ParsePrivateKey(pemBytes []byte) (Signer, error)

ParsePrivateKey returns a Signer from a PEM encoded private key. It supports the same keys as ParseRawPrivateKey.

func ParsePrivateKeyWithPassphrase 

func ParsePrivateKeyWithPassphrase(pemBytes, passPhrase []byte) (Signer, error)

ParsePrivateKeyWithPassphrase returns a Signer from a PEM encoded private key and passphrase. It supports the same keys as ParseRawPrivateKeyWithPassphrase.

type TerminalModes 

type TerminalModes map[uint8]uint32

type Waitmsg 

type Waitmsg struct {
	// contains filtered or unexported fields
}

Waitmsg stores the information about an exited remote command as reported by Wait.

func (Waitmsg) ExitStatus 

func (w Waitmsg) ExitStatus() int

ExitStatus returns the exit status of the remote command.

func (Waitmsg) Lang 

func (w Waitmsg) Lang() string

Lang returns the language tag. See RFC 3066

func (Waitmsg) Msg 

func (w Waitmsg) Msg() string

Msg returns the exit message given by the remote command

func (Waitmsg) Signal 

func (w Waitmsg) Signal() string

Signal returns the exit signal of the remote command if it was terminated violently.

func (Waitmsg) String 

func (w Waitmsg) String() string

Source Files

View all Source files

Directories

Path Synopsis
Package agent implements the ssh-agent protocol, and provides both a client and a server.
 Package agent implements the ssh-agent protocol, and provides both a client and a server.
Package knownhosts implements a parser for the OpenSSH known_hosts host key database, and provides utility functions for writing OpenSSH compliant known_hosts files.
 Package knownhosts implements a parser for the OpenSSH known_hosts host key database, and provides utility functions for writing OpenSSH compliant known_hosts files.
Package terminal provides support functions for dealing with terminals, as commonly found on UNIX systems.
 Package terminal provides support functions for dealing with terminals, as commonly found on UNIX systems.
Package test contains integration tests for the github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh package.
 Package test contains integration tests for the github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh package.

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