sshego

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README

sshego, a usable ssh library for Go

executive summary

Google's "golang.org/x/crypto/ssh" library offers a fantastic full implementation of the ssh client and server protocols. However this library is minimalistic by design, cumbersome to figure out how to use with RSA keys, and needs additional code to support support tunneling and receiving connections as an sshd.

sshego bridges this usability gap, providing a drop-in Go library to secure your tcp connections. In places sshego can be used in preference to a virtual-private-network (VPN), for both convenience and speed. Moreover the SSH protocol's man-in-the-middle attack protection is better than a VPN in almost all cases.

usable three-factor auth in an embeddable sshd

For strong security, our embedded sshd offers three-factor auth (3FA). The three security factors are: a passphrase ("what you know"); a 6-digit Google authenticator code (TOTP/RFC 6238; "what you have": your phone); and the use of PKI in the form of 4096-bit RSA keys.

To promote strong passphrases, we follow the inspiration of https://xkcd.com/936/, and offer a user- friendly 3-word starting prompt (the user completes the sentence) to spark the user's imagination in creating a strong and memorizable passphrase. Passphrases of up to 100 characters are supported.

Although not for the super-security conscious, if desired and configured, passphrases can automatically be backed up to email (via the Mailgun email service).

On new account creation with gosshtun -adduser yourlogin, we will attempt to pop-up the QR-code on your local desktop for quick Google Authenticator setup on your phone.

introducing sshego: a gopher's do-it-yourself ssh tunneling library

sshego is a golang (Go) library for ssh tunneling (secure port forwarding). It also offers an embeddable 3-factor authentication sshd server, which can be useful for securing reverse forwards.

This means you can easily create an ssh-based vpn with 3-factor authentication requrirements: the embedded sshd requires passphrase, RSA keys, and a TOTP Google Authenticator one-time password.

In addition to the libary, gosshtun is also a command line utility (see the cmd/ subdir) that demonstrates use of the library and may prove useful on its own.

The intent of having a Go library is so that it can be used to secure (via SSH tunnel) any other traffic that your Go application would normally have to do over cleartext TCP.

While you could always run a tunnel as a separate process, by running the tunnel in process with your application, you know the tunnel is running when the process is running. It's just simpler to administer; only one thing to start instead of two.

Also this is much simpler, and much faster, than using a virtual private network (VPN). For a speed comparison, consider [1] where SSH is seen to be at least 2x faster than OpenVPN.

[1] http://serverfault.com/questions/653211/ssh-tunneling-is-faster-than-openvpn-could-it-be

In its principal use, sshego is the equivalent to using the ssh client and giving -L and/or -R. It acts like an ssh client without a remote shell; it simply tunnels other TCP connections securely.

For example,

gosshtun -listen 127.0.0.1:89  -sshd jumpy:55  -remote 10.0.1.5:80 -user alice -key ~/.ssh/id_rsa_nopw

is equivalent to

ssh -N -L 89:10.0.1.5:80 alice@jumpy -port 55

with the addendum that gosshtun requires the use of passwordless private -key file, and will never prompt you for a password at the keyboard. This makes it ideal for embedding inside your application to secure your (e.g. mysql, postgres, other cleartext) traffic. As many connections as you need will be multiplexed over the same ssh tunnel.

theory of operation

gosshtun and sshego will check the sshd server's host key. We prevent MITM attacks by only allowing new servers if -new (a.k.a. SshegoConfig.AddIfNotKnown == true) is given.

When running the standalone gosshtun to test a foward, you should give -new only once at setup time.

Then the lack of -new protects you on subsequent runs, because the server's host key must match what we were given the very first time.

flags accepted, see gosshtun -h for complete list

Usage of gosshtun:
  -cfg string
        path to our config file
  -esshd string
        (optional) start an in-process embedded sshd (server),
        binding this host:port, with both RSA key and 2FA
        checking; useful for securing -revfwd connections.
  -esshd-host-db string
        (only matters if -esshd is also given) path
        to database holding sshd persistent state
        such as our host key, registered 2FA secrets, etc.
        (default "$HOME/.ssh/.sshego.sshd.db")        
  -key string
        private key for sshd login (default "$HOME/.ssh/id_rsa_nopw")
  -known-hosts string
        path to gosshtun's own known-hosts file (default
        "$HOME/.ssh/.sshego.cli.known.hosts")
  -listen string
        (forward tunnel) We listen on this host:port locally,
        securely tunnel that traffic to sshd, then send it
        cleartext to -remote. The forward tunnel is active
        if and only if -listen is given.
  -new
        allow connecting to a new sshd host key, and store it
        for future reference. Otherwise prevent MITM attacks by
        rejecting unknown hosts.
  -quiet
        if -quiet is given, we don't log to stdout as each
        connection is made. The default is false; we log
        each tunneled connection.        
  -remote string
        (forward tunnel) After traversing the secured forward
        tunnel, -listen traffic flows in cleartext from the
        sshd to this host:port. The foward tunnel is active
        only if -listen is given too.
  -revfwd string
        (reverse tunnel) The gosshtun application will receive
        securely tunneled connections from -revlisten on the
        sshd side, and cleartext forward them to this host:port.
        For security, it is recommended that this be 127.0.0.1:22,
        so that the sshd service on your gosshtun host
        authenticates all remotely initiated traffic.
        See also the -esshd option which can be used to
        secure the -revfwd connection as well.
        The reverse tunnel is active only if -revlisten is given
        too. (default "127.0.0.1:22")
  -revlisten string
        (reverse tunnel) The sshd will listen on this host:port,
        securely tunnel those connections to the gosshtun application,
        whence they will cleartext connect to the -revfwd address.
        The reverse tunnel is active if and only if -revlisten is given.  
  -sshd string
        The remote sshd host:port that we establish a secure tunnel to;
        our public key must have been already deployed there.
  -user string
        username for sshd login (default is $USER)
  -v    verbose debug mode
  -write-config string
        (optional) write our config to this path before doing
        connections

installation

go get github.com/glycerine/sshego/...

example use of the command

$ gosshtun -listen localhost:8888 -sshd 10.0.1.68:22 -remote 127.0.0.1:80

means the following two network hops will happen, when a local browser connects to localhost:8888

                       `gosshtun`             `sshd`
local browser ----> localhost:8888 --(a)--> 10.0.1.68:22 --(b)--> 127.0.0.1:80
  `host A`             `host A`               `host B`              `host B`

where (a) takes place inside the previously established ssh tunnel.

Connection (b) takes place over basic, un-adorned, un-encrypted TCP/IP. Of course you could always run gosshtun again on the remote host to secure the additional hop as well, but typically -remote is aimed at the 127.0.0.1, which will be internal to the remote host itself and so needs no encryption.

specifying username to login to sshd host with

The -user flag should be used if your local $USER is different from that on the sshd host.

source code for gosshtun command

See github.com/glycerine/sshego/cmd/gosshtun/main.go for the source code. This also serves as an example of how to use the library.

host key storage location (default)

~/.ssh/.sshego.known.hosts.json.snappy

prep before running

a) install your passwordless ssh-private key in ~/.ssh/id_rsa_nopw or use -key to say where it is.

b) add the corresponding public key to the user's .ssh/authorized_keys file on the sshd host.

config file format

a) see demo.env for an example

b) run gosshtun -write-config - to generate a sample config file to stdout

c) comments are allowed; lines must start with #, comments continue until end-of-line

d) fields recognized (see gosshtun -write-config - for a full list)

#
# config file for sshego:
#
SSHD_ADDR="1.2.3.4:22"
FWD_LISTEN_ADDR="127.0.0.1:8888"
FWD_REMOTE_ADDR="127.0.0.1:22"
REV_LISTEN_ADDR=""
REV_REMOTE_ADDR=""
SSHD_LOGIN_USERNAME="$USER"
SSH_PRIVATE_KEY_PATH="$HOME/.ssh/id_rsa_nopw"
SSH_KNOWN_HOSTS_PATH="$HOME/.ssh/.sshego.known.hosts"
#
# optional in-process sshd
#
EMBEDDED_SSHD_HOST_DB_PATH="$HOME/.ssh/.sshego.sshd.db"
EMBEDDED_SSHD_LISTEN_ADDR="127.0.0.1:2022"

d) special environment reads

  • The SSHD_LOGIN_USERNAME will subsitute $USER from the environment, if present.

  • The *PATH keys will substitute $HOME from the environment, if present.

MIT license

See the LICENSE file.

Author

Jason E. Aten, Ph.D.

Documentation

Overview

Package sshego is a golang libary that does secure port forwarding over ssh.

Also `gosshtun` is a command line utility included here that demonstrates use of the library; and may be useful standalone.

The intent of having a Go library is so that it can be used to secure (via SSH tunnel) any other traffic that your Go application would normally have to do over cleartext TCP.

While you could always run a tunnel as a separate process, by running the tunnel in process with your application, you know the tunnel is running when the process is running. It's just simpler to administer; only one thing to start instead of two.

Also this is much simpler, and much faster, than using a virtual private network (VPN). For a speed comparison, consider [1] where SSH is seen to be at least 2x faster than OpenVPN.

[1] http://serverfault.com/questions/653211/ssh-tunneling-is-faster-than-openvpn-could-it-be

In any case, you should realize that this is only an ssh client, and not an sshd server daemon. It is the equivalent to using the ssh client and giving `-L` and/or `-R`.

For example, 

gosshtun -listen 127.0.0.1:89  -sshd jumpy:55  -remote 10.0.1.5:80 -user alice -key ~/.ssh/id_rsa_nopw

is equivalent to 

ssh -N -L 89:10.0.1.5:80 alice@jumpy -port 55

with the addendum that `gosshtun` requires the use of passwordless private `-key` file, and will never prompt you for a password at the keyboard. This makes it ideal for embedding inside your application to secure your (e.g. mysql, postgres, other cleartext) traffic. As many connections as you need will be multiplexed over the same ssh tunnel.

theory of operation

We check the sshd server's host key. We prevent MITM attacks by only allowing new servers if `-new` is given.

You should give `-new` only once at setup time.

Then the lack of `-new` can protect you on subsequent runs, because the server's host key must match what we were given the first time.

options 

$ gosshtun -h
Usage of gosshtun:
 -cfg string
       path to our config file
 -esshd string
       (optional) start an in-process embedded sshd (server),
       binding this host:port, with both RSA key and 2FA
       checking; useful for securing -revfwd connections.
 -esshd-host-db string
       (only matters if -esshd is also given) path
       to database holding sshd persistent state
       such as our host key, registered 2FA secrets, etc.
       (default "$HOME/.ssh/.sshego.sshd.db")
 -key string
       private key for sshd login (default "$HOME/.ssh/id_rsa_nopw")
 -known-hosts string
       path to gosshtun's own known-hosts file (default
       "$HOME/.ssh/.sshego.cli.known.hosts")
 -listen string
       (forward tunnel) We listen on this host:port locally,
       securely tunnel that traffic to sshd, then send it
       cleartext to -remote. The forward tunnel is active
       if and only if -listen is given.
 -new
       allow connecting to a new sshd host key, and store it
       for future reference. Otherwise prevent MITM attacks by
       rejecting unknown hosts.
 -quiet
       if -quiet is given, we don't log to stdout as each
       connection is made. The default is false; we log
       each tunneled connection.
 -remote string
       (forward tunnel) After traversing the secured forward
       tunnel, -listen traffic flows in cleartext from the
       sshd to this host:port. The foward tunnel is active
       only if -listen is given too.
 -revfwd string
       (reverse tunnel) The gosshtun application will receive
       securely tunneled connections from -revlisten on the
       sshd side, and cleartext forward them to this host:port.
       For security, it is recommended that this be 127.0.0.1:22,
       so that the sshd service on your gosshtun host
       authenticates all remotely initiated traffic.
       See also the -esshd option which can be used to
       secure the -revfwd connection as well.
       The reverse tunnel is active only if -revlisten is given
       too. (default "127.0.0.1:22")
 -revlisten string
       (reverse tunnel) The sshd will listen on this host:port,
       securely tunnel those connections to the gosshtun application,
       whence they will cleartext connect to the -revfwd address.
       The reverse tunnel is active if and only if -revlisten is given.
 -sshd string
       The remote sshd host:port that we establish a secure tunnel to;
       our public key must have been already deployed there.
 -user string
       username for sshd login (default is $USER)
 -v    verbose debug mode
 -write-config string
       (optional) write our config to this path before doing
       connections
$

example use of the command 

$ gosshtun -listen localhost:8888 -sshd 10.0.1.68:22 -remote 127.0.0.1:80

means the following two network hops will happen, when a local browser connects to localhost:8888 

                       `gosshtun`             `sshd`
local browser ----> localhost:8888 --(a)--> 10.0.1.68:22 --(b)--> 127.0.0.1:80
  `host A`             `host A`               `host B`              `host B`

where (a) takes place inside the previously established ssh tunnel.

Connection (b) takes place over basic, un-adorned, un-encrypted TCP/IP. Of course you could always run `gosshtun` again on the remote host to secure the additional hop as well, but typically -remote is aimed at the 127.0.0.1, which will be internal to the remote host itself and so needs no encryption.

Index

Constants

This section is empty.

Variables

View Source 
var DelUserCmd = []byte("01DELUSER___")
View Source 
var DelUserCmdStr = string(DelUserCmd)
View Source 
var DelUserReplyFailed = []byte("01REPLY_FAIL")
View Source 
var DelUserReplyOK = []byte("01REPLY_OK__")
View Source 
var ErrCouldNotAquirePort = fmt.Errorf("could not acquire " +
	"our port before the deadline")
View Source 
var NewUserCmd = []byte("00NEWUSER___")
View Source 
var NewUserCmdStr = string(NewUserCmd)
View Source 
var NewUserReply = []byte("00REPLY_____")
View Source 
var Verbose bool

Verbose can be set to true for debug output. For production builds it should be set to false, the default.

Functions

func CryptoRandBytes 

func CryptoRandBytes(n int) []byte

func CryptoRandInt64 

func CryptoRandInt64() int64

Use crypto/rand to get an random int64

func CryptoRandNonNegInt 

func CryptoRandNonNegInt(n int64) int64

func Fingerprint 

func Fingerprint(k ssh.PublicKey) string

Fingerprint performs a SHA256 BASE64 fingerprint of the PublicKey, similar to OpenSSH. See: https://anongit.mindrot.org/openssh.git/commit/?id=56d1c83cdd1ac

func GenRSAKeyPair 

func GenRSAKeyPair(rsaFile string, bits int, email string) (priv *rsa.PrivateKey, sshPriv ssh.Signer, err error)

GenRSAKeyPair generates an RSA keypair of length bits. If rsa_file != "", we write the private key to rsa_file and the public key to rsa_file + ".pub". If rsa_file == "" the keys are not written to disk.

func GenRSAKeyPairCrypt 

func GenRSAKeyPairCrypt(rsaFile string, bits int, password string) (priv *rsa.PrivateKey, sshPriv ssh.Signer, err error)

TODO: Finish this-- specified but password based encryption not implemented. GenRSAKeyPairCrypt generates an RSA keypair of length bits. If rsa_file != "", we write the private key to rsa_file and the public key to rsa_file + ".pub". If rsa_file == "" the keys are not written to disk. The private key is encrypted with the password.

func GetExternalIP 

func GetExternalIP() string

GetExternalIP tries to determine the external IP address used on this host.

func IsRoutableIPv4 

func IsRoutableIPv4(ip string) bool

IsRoutableIPv4 returns true if the string in ip represents an IPv4 address that is not private. See http://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces for the numeric ranges that are private. 127.0.0.1, 192.168.0.1, and 172.16.0.1 are examples of non-routables IP addresses.

func KnownHostsEqual 

func KnownHostsEqual(a, b *KnownHosts) (bool, error)

KnownHostsEqual compares two instances of KnownHosts structures for equality.

func LoadRSAPrivateKey 

func LoadRSAPrivateKey(path string) (privkey ssh.Signer, err error)

LoadRSAPrivateKey reads a private key from path on disk.

func LoadRSAPrivateKeyCrypt 

func LoadRSAPrivateKeyCrypt(path string, password string) (privkey ssh.Signer, err error)

TODO: Finish this-- specified but password based encryption not implemented. LoadRSAPrivateKey reads a private key from path on disk.

func LoadRSAPublicKey 

func LoadRSAPublicKey(path string) (pubkey ssh.PublicKey, err error)

LoadRSAPublicKey reads a public key from path on disk. By convention these keys end in '.pub', but that is not verified here.

func PromptForPassword 

func PromptForPassword(username string) (pw string, err error)

PromptForPassword ask

func RSAToSSHPublicKey 

func RSAToSSHPublicKey(pubkey *rsa.PublicKey) []byte

RSAToSSHPublicKey convert an RSA Public Key to the SSH authorized_keys format.

func ScryptHash 

func ScryptHash(password string) []byte

func SetWinsize 

func SetWinsize(fd uintptr, w, h uint32)

SetWinsize sets the size of the given pty.

Types

type AddrHostPort 

type AddrHostPort struct {
	Title    string
	Addr     string
	Host     string
	Port     uint64
	Required bool
}

AddrHostPort is used to specify tunnel endpoints.

func (*AddrHostPort) ParseAddr 

func (a *AddrHostPort) ParseAddr() error

ParseAddr fills Host and Port from Addr, breaking Addr apart at the ':' using net.SplitHostPort()

type AtomicUserMap 

type AtomicUserMap struct {
	U map[string]*User
	// contains filtered or unexported fields
}

func NewAtomicUserMap 

func NewAtomicUserMap() *AtomicUserMap

func (*AtomicUserMap) DecodeMsg 

func (z *AtomicUserMap) DecodeMsg(dc *msgp.Reader) (err error)

DecodeMsg implements msgp.Decodable

func (*AtomicUserMap) Del 

func (m *AtomicUserMap) Del(key string)

func (*AtomicUserMap) EncodeMsg 

func (z *AtomicUserMap) EncodeMsg(en *msgp.Writer) (err error)

EncodeMsg implements msgp.Encodable

func (*AtomicUserMap) Get 

func (m *AtomicUserMap) Get(key string) *User

func (*AtomicUserMap) Get2 

func (m *AtomicUserMap) Get2(key string) (*User, bool)

func (*AtomicUserMap) MarshalMsg 

func (z *AtomicUserMap) MarshalMsg(b []byte) (o []byte, err error)

MarshalMsg implements msgp.Marshaler

func (*AtomicUserMap) Msgsize 

func (z *AtomicUserMap) Msgsize() (s int)

Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message

func (*AtomicUserMap) Set 

func (m *AtomicUserMap) Set(key string, val *User)

func (*AtomicUserMap) UnmarshalMsg 

func (z *AtomicUserMap) UnmarshalMsg(bts []byte) (o []byte, err error)

UnmarshalMsg implements msgp.Unmarshaler

type AuthState 

type AuthState struct {
	HostKey ssh.Signer
	OneTime *TOTP

	AuthorizedKeysMap map[string]bool

	PrivateKeys map[string]interface{}
	Signers     map[string]ssh.Signer
	PublicKeys  map[string]ssh.PublicKey

	Cert *ssh.Certificate
}

AuthState holds the authorization information that doesn't change after startup; each fresh PerAttempt gets a pointer to one of these. Currently assumes only one user.

func NewAuthState 

func NewAuthState(w *TOTP) *AuthState

func (*AuthState) LoadHostKey 

func (a *AuthState) LoadHostKey(path string) error

func (*AuthState) LoadPublicKeys 

func (a *AuthState) LoadPublicKeys(authorizedKeysPath string) error

type CommandRecv 

type CommandRecv struct {
	Done chan bool
	// contains filtered or unexported fields
}

func (*CommandRecv) Start 

func (cr *CommandRecv) Start() error

type DialConfig 

type DialConfig struct {

	// ClientKnownHostsPath is the path to the file
	// on client's disk that holds the known server keys.
	ClientKnownHostsPath string

	// cached to avoid a disk read, we only read
	// from ClientKnownHostsPath if KnownHosts is nil.
	// Users of DialConfig can leave this nil and
	// simply provide ClientKnownHostsPath. It is
	// exposed in case you need to invalidate the
	// cache and start again.
	KnownHosts *KnownHosts

	// the username to login under
	Mylogin string

	// the path on the local file system (client side) from
	// which to read the client's RSA private key.
	RsaPath string

	// the time-based one-time password configuration
	TotpUrl string

	// Pw is the passphrase
	Pw string

	// which sshd to connect to, host and port.
	Sshdhost string
	Sshdport uint64

	// DownstreamHostPort is the host:port string of
	// the tcp address to which the sshd should forward
	// our connection to.
	DownstreamHostPort string

	// TofuAddIfNotKnown, for maximum security,
	// should be always left false and
	// the host key database should be configured
	// manually. If true, the client trusts the server's
	// provided key and stores it, which creates
	// vulnerability to a MITM attack.
	//
	// TOFU stands for Trust-On-First-Use.
	//
	// If set to true, Dial() will set TofuAddIfNotKnown back
	// to false after storing the server (or
	// attacker) provided key and retying the
	// connection attempt with the newly stored
	// key. This prevents MITM after the
	// first contact if the DialConfig is reused.
	TofuAddIfNotKnown bool

	// DoNotUpdateSshKnownHosts prevents writing
	// to the file given by ClientKnownHostsPath, if true.
	DoNotUpdateSshKnownHosts bool
}

DialConfig provides Dial() with what it needs in order to establish an encrypted and authenticated ssh connection.

func (*DialConfig) Dial 

func (dc *DialConfig) Dial() (net.Conn, *ssh.Client, error)

Dial is a convenience method for contacting an sshd over tcp and creating a direct-tcpip encrypted stream. It is a simple two-step sequence of calling dc.Cfg.SSHConnect() and then calling Dial() on the returned *ssh.Client.

PRE: dc.Cfg.KnownHosts should already be instantiated. To prevent MITM attacks, the host we contact at hostport must have its server key must be already in the KnownHosts.

dc.RsaPath is the path to the our (the client's) rsa private key file.

dc.DownstreamHostPort is the host:port tcp address string to which the sshd should forward our connection after successful authentication.

type Esshd 

type Esshd struct {
	Done chan bool
	// contains filtered or unexported fields
}

Esshd is our embedded sshd server, running from inside this libary.

func (*Esshd) NewCommandRecv 

func (e *Esshd) NewCommandRecv() *CommandRecv

func (*Esshd) Start 

func (e *Esshd) Start()

func (*Esshd) Stop 

func (e *Esshd) Stop()

type Forwarder 

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

Forwarder represents one bi-directional forward (sshego to sshd) tcp connection.

func NewForward 

func NewForward(cfg *SshegoConfig, sshClientConn *ssh.Client, fromBrowser net.Conn) *Forwarder

NewForward is called to produce a Forwarder structure for each new forward connection.

type HostDb 

type HostDb struct {

	// Users: key is MyLogin; value is *User.
	Users *AtomicUserMap

	HostPrivateKeyPath string
	// contains filtered or unexported fields
}

func (*HostDb) AddUser 

func (h *HostDb) AddUser(mylogin, myemail, pw, issuer, fullname string) (toptPath, qrPath, rsaPath string, err error)

func (*HostDb) DecodeMsg 

func (z *HostDb) DecodeMsg(dc *msgp.Reader) (err error)

DecodeMsg implements msgp.Decodable

func (*HostDb) DelUser 

func (h *HostDb) DelUser(mylogin string) error

func (*HostDb) EncodeMsg 

func (z *HostDb) EncodeMsg(en *msgp.Writer) (err error)

EncodeMsg implements msgp.Encodable

func (*HostDb) MarshalMsg 

func (z *HostDb) MarshalMsg(b []byte) (o []byte, err error)

MarshalMsg implements msgp.Marshaler

func (*HostDb) Msgsize 

func (z *HostDb) Msgsize() (s int)

Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message

func (*HostDb) UnmarshalMsg 

func (z *HostDb) UnmarshalMsg(bts []byte) (o []byte, err error)

UnmarshalMsg implements msgp.Unmarshaler

func (*HostDb) UserExists 

func (h *HostDb) UserExists(mylogin string) bool

UserExists is used by sshego/cmd/gosshtun/main.go

func (*HostDb) ValidEmail 

func (h *HostDb) ValidEmail(myemail string) (bool, error)

func (*HostDb) ValidLogin 

func (h *HostDb) ValidLogin(login string) (bool, error)

type HostState 

type HostState int

HostState recognizes host keys are legitimate or impersonated, new, banned, or consitent with what we've seen before and so OK. 

const AddedNew HostState = 4

AddedNew means the -new flag was given and we allowed the addition of a new host-key for the first time. 

const Banned HostState = 1

Banned means the host has been marked as forbidden. 

const KnownOK HostState = 2

KnownOK means the host key matches one we have previously allowed. 

const KnownRecordMismatch HostState = 3

KnownRecordMismatch means we have a records for this IP/host-key, but either the IP or the host-key has varied and so it could be a Man-in-the-middle attack. 

const Unknown HostState = 0

Unknown means we don't have a matching stored host key.

func (HostState) String 

func (s HostState) String() string

type KnownHosts 

type KnownHosts struct {
	Hosts map[string]*ServerPubKey

	// FilepathPrefix doesn't have the .json.snappy suffix on it.
	FilepathPrefix string

	PersistFormatSuffix string

	// PersistFormat is the format indicator
	PersistFormat KnownHostsPersistFormat

	// NoSave means we don't touch the files we read from
	NoSave bool
	// contains filtered or unexported fields
}

KnownHosts represents in Hosts a hash map of host identifier (ip or name) and the corresponding public key for the server. It corresponds to the ~/.ssh/known_hosts file.

func LoadSshKnownHosts 

func LoadSshKnownHosts(path string) (*KnownHosts, error)

LoadSshKnownHosts reads a ~/.ssh/known_hosts style file from path, see the SSH_KNOWN_HOSTS FILE FORMAT section of http://manpages.ubuntu.com/manpages/zesty/en/man8/sshd.8.html or the local sshd(8) man page.

func NewKnownHosts 

func NewKnownHosts(filepath string, format KnownHostsPersistFormat) (*KnownHosts, error)

NewKnownHosts creats a new KnownHosts structure. filepathPrefix does not include the PersistFormat suffix. If filepathPrefix + defaultFileFormat() exists as a file on disk, then we read the contents of that file into the new KnownHosts.

The returned KnownHosts will remember the filepathPrefix for future saves.

func (*KnownHosts) AddNeeded 

func (h *KnownHosts) AddNeeded(addIfNotKnown, allowOneshotConnect bool, hostname string, remote net.Addr, strPubBytes string, key ssh.PublicKey, record *ServerPubKey) (HostState, *ServerPubKey, error)

func (*KnownHosts) Close 

func (h *KnownHosts) Close()

Close cleans up and prepares for shutdown. It calls h.Sync() to write the state to disk.

func (*KnownHosts) HostAlreadyKnown 

func (h *KnownHosts) HostAlreadyKnown(hostname string, remote net.Addr, key ssh.PublicKey, pubBytes []byte, addIfNotKnown bool, allowOneshotConnect bool) (HostState, *ServerPubKey, error)

HostAlreadyKnown checks the given host details against our known hosts file.

func (*KnownHosts) Sync 

func (h *KnownHosts) Sync() (err error)

Sync writes the contents of the KnownHosts structure to the file h.FilepathPrefix + h.PersistFormat (for json/gob); to just h.FilepathPrefix for "ssh_known_hosts" format.

type KnownHostsPersistFormat 

type KnownHostsPersistFormat int
const (
	KHJson KnownHostsPersistFormat = 0
	KHGob  KnownHostsPersistFormat = 1
	KHSsh  KnownHostsPersistFormat = 2
)

type LoginRecord 

type LoginRecord struct {
	FirstTm       time.Time
	LastTm        time.Time
	SeenCount     int64
	AcceptedCount int64
	PubFinger     string
}

LoginRecord is per public key.

func (*LoginRecord) DecodeMsg 

func (z *LoginRecord) DecodeMsg(dc *msgp.Reader) (err error)

DecodeMsg implements msgp.Decodable

func (*LoginRecord) EncodeMsg 

func (z *LoginRecord) EncodeMsg(en *msgp.Writer) (err error)

EncodeMsg implements msgp.Encodable

func (*LoginRecord) MarshalMsg 

func (z *LoginRecord) MarshalMsg(b []byte) (o []byte, err error)

MarshalMsg implements msgp.Marshaler

func (*LoginRecord) Msgsize 

func (z *LoginRecord) Msgsize() (s int)

Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message

func (LoginRecord) String 

func (r LoginRecord) String() string

func (*LoginRecord) UnmarshalMsg 

func (z *LoginRecord) UnmarshalMsg(bts []byte) (o []byte, err error)

UnmarshalMsg implements msgp.Unmarshaler

type MailgunConfig 

type MailgunConfig struct {

	// MAILGUN_DOMAIN
	Domain string

	// MAILGUN_PUBLIC_API_KEY
	PublicApiKey string

	//MAILGUN_SECRET_API_KEY
	SecretApiKey string
}

MailgunConfig sets up sending backup emails through Mailgun. See https://mailgun.com.

func (*MailgunConfig) DefineFlags 

func (c *MailgunConfig) DefineFlags(fs *flag.FlagSet)

DefineFlags should be called before myflags.Parse().

func (*MailgunConfig) LoadConfig 

func (c *MailgunConfig) LoadConfig(path string) error

LoadConfig reads configuration from a file, expecting KEY=value pair on each line; values optionally enclosed in double quotes.

func (*MailgunConfig) SaveConfig 

func (c *MailgunConfig) SaveConfig(fd io.Writer) error

SaveConfig writes the config structs to the given io.Writer

func (*MailgunConfig) SendEmail 

func (c *MailgunConfig) SendEmail(senderEmail, subject, plain, html, recipEmail string) (string, error)

func (*MailgunConfig) ValidateConfig 

func (c *MailgunConfig) ValidateConfig() error

ValidateConfig should be called after myflags.Parse().

type PerAttempt 

type PerAttempt struct {
	PublicKeyOK bool
	OneTimeOK   bool

	User   *User
	State  *AuthState
	Config *ssh.ServerConfig
	// contains filtered or unexported fields
}

PerAttempt holds the auth state that should be reset anew on each login attempt; plus a pointer to the invariant State.

func NewPerAttempt 

func NewPerAttempt(s *AuthState, cfg *SshegoConfig) *PerAttempt

func (*PerAttempt) AuthLogCallback 

func (a *PerAttempt) AuthLogCallback(conn ssh.ConnMetadata, method string, err error)

func (*PerAttempt) KeyboardInteractiveCallback 

func (a *PerAttempt) KeyboardInteractiveCallback(conn ssh.ConnMetadata, challenge ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error)

func (*PerAttempt) NoteLogin 

func (a *PerAttempt) NoteLogin(user *User, now time.Time, conn ssh.ConnMetadata)

func (*PerAttempt) PerConnection 

func (a *PerAttempt) PerConnection(nConn net.Conn)

func (*PerAttempt) PublicKeyCallback 

func (a *PerAttempt) PublicKeyCallback(c ssh.ConnMetadata, providedPubKey ssh.PublicKey) (perm *ssh.Permissions, rerr error)

func (*PerAttempt) SetTripleConfig 

func (a *PerAttempt) SetTripleConfig()

SetTripleConfig establishes an a.State.Config that requires *both* public key and one-time password validation.

func (*PerAttempt) SetupAuthRequirements 

func (a *PerAttempt) SetupAuthRequirements()

type Reverse 

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

Reverse represents one bi-directional (initiated at sshd, tunneled to sshego) tcp connection.

type ServerPubKey 

type ServerPubKey struct {
	Hostname string

	// HumanKey is a serialized and readable version of Key, the key for Hosts map in KnownHosts.
	HumanKey     string
	ServerBanned bool

	// reading ~/.ssh/known_hosts
	Markers                  string
	Hostnames                string
	SplitHostnames           map[string]bool
	Keytype                  string
	Base64EncodededPublicKey string
	Comment                  string
	Port                     string
	LineInFileOneBased       int

	// if AlreadySaved, then we don't need to append.
	AlreadySaved bool
	// contains filtered or unexported fields
}

ServerPubKey stores the RSA public keys for a particular known server. This structure is stored in KnownHosts.Hosts.

func (*ServerPubKey) AddHostPort 

func (prior *ServerPubKey) AddHostPort(hp string)

type SshegoConfig 

type SshegoConfig struct {
	ConfigPath string

	SSHdServer    AddrHostPort // the sshd host we are logging into remotely.
	LocalToRemote TunnelSpec
	RemoteToLocal TunnelSpec

	Debug bool

	AddIfNotKnown bool

	Username             string
	PrivateKeyPath       string
	ClientKnownHostsPath string

	KnownHosts *KnownHosts

	WriteConfigOut string

	// if -write-config is all we are doing
	WriteConfigOnly bool

	Quiet bool

	Esshd                  *Esshd
	EmbeddedSSHdHostDbPath string
	EmbeddedSSHd           AddrHostPort // optional local sshd, embedded.

	HostDb *HostDb

	AddUser string
	DelUser string

	SshegoSystemMutexPortString string
	SshegoSystemMutexPort       int

	MailCfg MailgunConfig

	// allow less than 3FA
	// Not recommended, but possible.
	SkipTOTP       bool
	SkipPassphrase bool
	SkipRSA        bool

	BitLenRSAkeys int

	DirectTcp bool
	// contains filtered or unexported fields
}

SshegoConfig is the top level, main config

func NewSshegoConfig 

func NewSshegoConfig() *SshegoConfig

func (*SshegoConfig) DefineFlags 

func (c *SshegoConfig) DefineFlags(fs *flag.FlagSet)

DefineFlags should be called before myflags.Parse().

func (*SshegoConfig) GenAuthString 

func (cfg *SshegoConfig) GenAuthString() string

func (*SshegoConfig) LoadConfig 

func (c *SshegoConfig) LoadConfig(path string) error

LoadConfig reads configuration from a file, expecting KEY=value pair on each line; values optionally enclosed in double quotes.

func (*SshegoConfig) NewEsshd 

func (cfg *SshegoConfig) NewEsshd() *Esshd

NewEsshd sets cfg.Esshd with a newly constructed Esshd. does NewHostDb() internally.

func (*SshegoConfig) NewHostDb 

func (cfg *SshegoConfig) NewHostDb() error

func (*SshegoConfig) SSHConnect 

func (cfg *SshegoConfig) SSHConnect(h *KnownHosts, username string, keypath string, sshdHost string, sshdPort uint64, passphrase string, toptUrl string) (*ssh.Client, error)

SSHConnect is the main entry point for the gosshtun library, establishing an ssh tunnel between two hosts.

passphrase and toptUrl (one-time password used in challenge/response) are optional, but will be offered to the server if set.

func (*SshegoConfig) SaveConfig 

func (c *SshegoConfig) SaveConfig(fd io.Writer) error

SaveConfig writes the config structs to the given io.Writer

func (*SshegoConfig) StartNewReverse 

func (cfg *SshegoConfig) StartNewReverse(sshClientConn *ssh.Client, fromRemote net.Conn) (*Reverse, error)

StartNewReverse is invoked once per reverse connection made to generate a new Reverse structure.

func (*SshegoConfig) StartupForwardListener 

func (cfg *SshegoConfig) StartupForwardListener(sshClientConn *ssh.Client) error

StartupForwardListener is called when a forward tunnel is the be listened for.

func (*SshegoConfig) StartupReverseListener 

func (cfg *SshegoConfig) StartupReverseListener(sshClientConn *ssh.Client) error

StartupReverseListener is called when a reverse tunnel is requested, to listen and tunnel those connections.

func (*SshegoConfig) TcpClientUserAdd 

func (cfg *SshegoConfig) TcpClientUserAdd(user *User) (toptPath, qrPath, rsaPath string, err error)

func (*SshegoConfig) TcpClientUserDel 

func (cfg *SshegoConfig) TcpClientUserDel(user *User) error

func (*SshegoConfig) ValidateConfig 

func (c *SshegoConfig) ValidateConfig() error

ValidateConfig should be called after myflags.Parse().

type TOTP 

type TOTP struct {
	UserEmail string
	Issuer    string
	Key       *otp.Key
	QRcodePng []byte
}

func NewTOTP 

func NewTOTP(userEmail, issuer string) (w *TOTP, err error)

func (*TOTP) IsValid 

func (w *TOTP) IsValid(passcode string, mylogin string) bool

func (*TOTP) LoadFromFile 

func (w *TOTP) LoadFromFile(path string) error

func (*TOTP) SaveToFile 

func (w *TOTP) SaveToFile(path string) (secretPath, qrPath string, err error)

func (*TOTP) String 

func (w *TOTP) String() string

type TcpPort 

type TcpPort struct {
	Port int
	Lsn  net.Listener
	// contains filtered or unexported fields
}

func (*TcpPort) Lock 

func (t *TcpPort) Lock(limitMsec int) error

func (*TcpPort) Unlock 

func (t *TcpPort) Unlock()

type TunnelSpec 

type TunnelSpec struct {
	Listen AddrHostPort
	Remote AddrHostPort
}

TunnelSpec represents either a forward or a reverse tunnel in SshegoConfig.

type User 

type User struct {
	MyEmail    string
	MyFullname string
	MyLogin    string

	PublicKeyPath  string
	PrivateKeyPath string
	TOTPpath       string
	QrPath         string

	Issuer string

	SeenPubKey map[string]LoginRecord

	ScryptedPassword []byte
	ClearPw          string // only on network, never on disk.
	TOTPorig         string

	FirstLoginTime time.Time
	LastLoginTime  time.Time
	LastLoginAddr  string
	IPwhitelist    []string
	DisabledAcct   bool
	// contains filtered or unexported fields
}

User represents a user authorized to login to the embedded sshd.

func NewUser 

func NewUser() *User

func (*User) DecodeMsg 

func (z *User) DecodeMsg(dc *msgp.Reader) (err error)

DecodeMsg implements msgp.Decodable

func (*User) EncodeMsg 

func (z *User) EncodeMsg(en *msgp.Writer) (err error)

EncodeMsg implements msgp.Encodable

func (*User) MarshalMsg 

func (z *User) MarshalMsg(b []byte) (o []byte, err error)

MarshalMsg implements msgp.Marshaler

func (*User) MatchingHashAndPw 

func (user *User) MatchingHashAndPw(password string) bool

func (*User) Msgsize 

func (z *User) Msgsize() (s int)

Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message

func (*User) RestoreTotp 

func (user *User) RestoreTotp()

func (*User) UnmarshalMsg 

func (z *User) UnmarshalMsg(bts []byte) (o []byte, err error)

UnmarshalMsg implements msgp.Unmarshaler

type Winsize 

type Winsize struct {
	Height uint16
	Width  uint16
	// contains filtered or unexported fields
}

Winsize stores the Height and Width of a terminal.

Source Files

View all Source files

Directories

Path Synopsis
cmd
gosshtun
manual-test-client
a simple test client.
 a simple test client.
manual-test-recv
a simple test receiver (server) to check that your direct-tcpip connections are coming through the sshd.
 a simple test receiver (server) to check that your direct-tcpip connections are coming through the sshd.

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