obfuscator

Documentation

Index

• Constants
• func DeriveTLSPassthroughKey(obfuscatedKey string) ([]byte, error)
• func MakeTLSPassthroughMessage(obfuscatedKey string) ([]byte, error)
• func VerifyTLSPassthroughMessage(passthroughKey, message []byte) bool
• type ObfuscatedSSHConn
  • func NewClientObfuscatedSSHConn(conn net.Conn, obfuscationKeyword string, ...) (*ObfuscatedSSHConn, error)
  • func NewObfuscatedSSHConn(mode ObfuscatedSSHConnMode, conn net.Conn, obfuscationKeyword string, ...) (*ObfuscatedSSHConn, error)
  • func NewServerObfuscatedSSHConn(conn net.Conn, obfuscationKeyword string, seedHistory *SeedHistory, ...) (*ObfuscatedSSHConn, error)
  • func (conn *ObfuscatedSSHConn) GetDerivedPRNG(salt string) (*prng.PRNG, error)
  • func (conn *ObfuscatedSSHConn) GetMetrics() common.LogFields
  • func (conn *ObfuscatedSSHConn) Read(buffer []byte) (int, error)
  • func (conn *ObfuscatedSSHConn) Write(buffer []byte) (int, error)
• type ObfuscatedSSHConnMode
• type ObfuscatedSSHReadState
• type ObfuscatedSSHWriteState
• type Obfuscator
  • func NewClientObfuscator(config *ObfuscatorConfig) (obfuscator *Obfuscator, err error)
  • func NewServerObfuscator(config *ObfuscatorConfig, clientIP string, clientReader io.Reader) (obfuscator *Obfuscator, err error)
  • func (obfuscator *Obfuscator) GetDerivedPRNG(salt string) (*prng.PRNG, error)
  • func (obfuscator *Obfuscator) GetPaddingLength() int
  • func (obfuscator *Obfuscator) ObfuscateClientToServer(buffer []byte)
  • func (obfuscator *Obfuscator) ObfuscateServerToClient(buffer []byte)
  • func (obfuscator *Obfuscator) SendSeedMessage() []byte
• type ObfuscatorConfig
• type SeedHistory
  • func NewSeedHistory(config *SeedHistoryConfig) *SeedHistory
  • func (h *SeedHistory) AddNew(strictMode bool, clientIP string, seedType string, seed []byte) (bool, *common.LogFields)
• type SeedHistoryConfig

Constants

const (
	HISTORY_SEED_TTL              = 24 * time.Hour
	HISTORY_SEED_MAX_ENTRIES      = 1000000
	HISTORY_CLIENT_IP_TTL         = 2 * time.Minute
	HISTORY_CLIENT_IP_MAX_ENTRIES = 10000
)

const (
	SSH_MAX_SERVER_LINE_LENGTH = 1024
	SSH_PACKET_PREFIX_LENGTH   = 5          // uint32 + byte
	SSH_MAX_PACKET_LENGTH      = 256 * 1024 // OpenSSH max packet length
	SSH_MSG_NEWKEYS            = 21
	SSH_MAX_PADDING_LENGTH     = 255 // RFC 4253 sec. 6
	SSH_PADDING_MULTIPLE       = 16  // Default cipher block size
)

const (
	OBFUSCATION_CONN_MODE_CLIENT = iota
	OBFUSCATION_CONN_MODE_SERVER
)

const (
	OBFUSCATION_READ_STATE_IDENTIFICATION_LINES = iota
	OBFUSCATION_READ_STATE_KEX_PACKETS
	OBFUSCATION_READ_STATE_FLUSH
	OBFUSCATION_READ_STATE_FINISHED
)

const (
	OBFUSCATION_WRITE_STATE_CLIENT_SEND_SEED_MESSAGE = iota
	OBFUSCATION_WRITE_STATE_SERVER_SEND_IDENTIFICATION_LINE_PADDING
	OBFUSCATION_WRITE_STATE_IDENTIFICATION_LINE
	OBFUSCATION_WRITE_STATE_KEX_PACKETS
	OBFUSCATION_WRITE_STATE_FINISHED
)

const (
	OBFUSCATE_SEED_LENGTH         = 16
	OBFUSCATE_KEY_LENGTH          = 16
	OBFUSCATE_HASH_ITERATIONS     = 6000
	OBFUSCATE_MAX_PADDING         = 8192
	OBFUSCATE_MAGIC_VALUE         = 0x0BF5CA7E
	OBFUSCATE_CLIENT_TO_SERVER_IV = "client_to_server"
	OBFUSCATE_SERVER_TO_CLIENT_IV = "server_to_client"
)

const (
	TLS_PASSTHROUGH_NONCE_SIZE   = 16
	TLS_PASSTHROUGH_KEY_SIZE     = 32
	TLS_PASSTHROUGH_MESSAGE_SIZE = 32
)

Functions

func DeriveTLSPassthroughKey

func DeriveTLSPassthroughKey(obfuscatedKey string) ([]byte, error)

DeriveTLSPassthroughKey derives a TLS passthrough key from a master obfuscated key. The resulting key can be cached and passed to VerifyTLSPassthroughMessage.

func MakeTLSPassthroughMessage

func MakeTLSPassthroughMessage(obfuscatedKey string) ([]byte, error)

MakeTLSPassthroughMessage generates a unique TLS passthrough message using the passthrough key derived from a master obfuscated key.

The passthrough message demonstrates knowledge of the obfuscated key.

func VerifyTLSPassthroughMessage

func VerifyTLSPassthroughMessage(passthroughKey, message []byte) bool

VerifyTLSPassthroughMessage checks that the specified passthrough message was generated using the passthrough key.

Types

type ObfuscatedSSHConn

type ObfuscatedSSHConn struct {
	net.Conn
	// contains filtered or unexported fields
}

ObfuscatedSSHConn wraps a Conn and applies the obfuscated SSH protocol to the traffic on the connection: https://github.com/brl/obfuscated-openssh/blob/master/README.obfuscation

ObfuscatedSSHConn is used to add obfuscation to golang's stock "ssh" client and server without modification to that standard library code. The underlying connection must be used for SSH traffic. This code injects the obfuscated seed message, applies obfuscated stream cipher transformations, and performs minimal parsing of the SSH protocol to determine when to stop obfuscation (after the first SSH_MSG_NEWKEYS is sent and received).

WARNING: doesn't fully conform to net.Conn concurrency semantics: there's no synchronization of access to the read/writeBuffers, so concurrent calls to one of Read or Write will result in undefined behavior.

func NewClientObfuscatedSSHConn

func NewClientObfuscatedSSHConn(
	conn net.Conn,
	obfuscationKeyword string,
	obfuscationPaddingPRNGSeed *prng.Seed,
	minPadding, maxPadding *int) (*ObfuscatedSSHConn, error)

NewClientObfuscatedSSHConn creates a client ObfuscatedSSHConn. See documentation in NewObfuscatedSSHConn.

func NewObfuscatedSSHConn

func NewObfuscatedSSHConn(
	mode ObfuscatedSSHConnMode,
	conn net.Conn,
	obfuscationKeyword string,
	obfuscationPaddingPRNGSeed *prng.Seed,
	minPadding, maxPadding *int,
	seedHistory *SeedHistory,
	irregularLogger func(
		clientIP string,
		err error,
		logFields common.LogFields)) (*ObfuscatedSSHConn, error)

NewObfuscatedSSHConn creates a new ObfuscatedSSHConn. The underlying conn must be used for SSH traffic and must have transferred no traffic.

In client mode, NewObfuscatedSSHConn does not block or initiate network I/O. The obfuscation seed message is sent when Write() is first called.

In server mode, NewObfuscatedSSHConn cannot completely initialize itself without the seed message from the client to derive obfuscation keys. So NewObfuscatedSSHConn blocks on reading the client seed message from the underlying conn.

obfuscationPaddingPRNGSeed is required and used only in OBFUSCATION_CONN_MODE_CLIENT mode and allows for optional replay of the same padding: both in the initial obfuscator message and in the SSH KEX sequence. In OBFUSCATION_CONN_MODE_SERVER mode, the server obtains its PRNG seed from the client's initial obfuscator message, resulting in the server replaying its padding as well.

seedHistory and irregularLogger are optional ObfuscatorConfig parameters used only in OBFUSCATION_CONN_MODE_SERVER.

func NewServerObfuscatedSSHConn

func NewServerObfuscatedSSHConn(
	conn net.Conn,
	obfuscationKeyword string,
	seedHistory *SeedHistory,
	irregularLogger func(
		clientIP string,
		err error,
		logFields common.LogFields)) (*ObfuscatedSSHConn, error)

NewServerObfuscatedSSHConn creates a server ObfuscatedSSHConn. See documentation in NewObfuscatedSSHConn.

func (*ObfuscatedSSHConn) GetDerivedPRNG

func (conn *ObfuscatedSSHConn) GetDerivedPRNG(salt string) (*prng.PRNG, error)

GetDerivedPRNG creates a new PRNG with a seed derived from the ObfuscatedSSHConn padding seed and distinguished by the salt, which should be a unique identifier for each usage context.

In OBFUSCATION_CONN_MODE_SERVER mode, the ObfuscatedSSHConn padding seed is obtained from the client, so derived PRNGs may be used to replay sequences post-initial obfuscator message.

func (*ObfuscatedSSHConn) GetMetrics

func (conn *ObfuscatedSSHConn) GetMetrics() common.LogFields

GetMetrics implements the common.MetricsSource interface.

func (*ObfuscatedSSHConn) Read

func (conn *ObfuscatedSSHConn) Read(buffer []byte) (int, error)

Read wraps standard Read, transparently applying the obfuscation transformations.

func (*ObfuscatedSSHConn) Write

func (conn *ObfuscatedSSHConn) Write(buffer []byte) (int, error)

Write wraps standard Write, transparently applying the obfuscation transformations.

type ObfuscatedSSHConnMode

type ObfuscatedSSHConnMode int

type ObfuscatedSSHReadState

type ObfuscatedSSHReadState int

type ObfuscatedSSHWriteState

type ObfuscatedSSHWriteState int

type Obfuscator

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

Obfuscator implements the seed message, key derivation, and stream ciphers for: https://github.com/brl/obfuscated-openssh/blob/master/README.obfuscation

Limitation: the RC4 cipher is vulnerable to ciphertext malleability and the "magic" value provides only weak authentication due to its small size. Increasing the size of the magic field will break compatibility with legacy clients. New protocols and schemes should not use this obfuscator.

func NewClientObfuscator

func NewClientObfuscator(
	config *ObfuscatorConfig) (obfuscator *Obfuscator, err error)

NewClientObfuscator creates a new Obfuscator, staging a seed message to be sent to the server (by the caller) and initializing stream ciphers to obfuscate data.

ObfuscatorConfig.PaddingPRNGSeed allows for optional replay of the obfuscator padding and must not be nil.

func NewServerObfuscator

func NewServerObfuscator(
	config *ObfuscatorConfig, clientIP string, clientReader io.Reader) (obfuscator *Obfuscator, err error)

NewServerObfuscator creates a new Obfuscator, reading a seed message directly from the clientReader and initializing stream ciphers to obfuscate data.

ObfuscatorConfig.PaddingPRNGSeed is not used, as the server obtains a PRNG seed from the client's initial obfuscator message; this scheme allows for optional replay of the downstream obfuscator padding.

The clientIP value is used by the SeedHistory, which retains client IP values for a short time. See SeedHistory documentation.

func (*Obfuscator) GetDerivedPRNG

func (obfuscator *Obfuscator) GetDerivedPRNG(salt string) (*prng.PRNG, error)

GetDerivedPRNG creates a new PRNG with a seed derived from the obfuscator padding seed and distinguished by the salt, which should be a unique identifier for each usage context.

For NewServerObfuscator, the obfuscator padding seed is obtained from the client, so derived PRNGs may be used to replay sequences post-initial obfuscator message.

func (*Obfuscator) GetPaddingLength

func (obfuscator *Obfuscator) GetPaddingLength() int

GetPaddingLength returns the client seed message padding length. Only valid for NewClientObfuscator.

func (*Obfuscator) ObfuscateClientToServer

func (obfuscator *Obfuscator) ObfuscateClientToServer(buffer []byte)

ObfuscateClientToServer applies the client RC4 stream to the bytes in buffer.

func (*Obfuscator) ObfuscateServerToClient

func (obfuscator *Obfuscator) ObfuscateServerToClient(buffer []byte)

ObfuscateServerToClient applies the server RC4 stream to the bytes in buffer.

func (*Obfuscator) SendSeedMessage

func (obfuscator *Obfuscator) SendSeedMessage() []byte

SendSeedMessage returns the seed message created in NewObfuscatorClient, removing the reference so that it may be garbage collected.

type ObfuscatorConfig

type ObfuscatorConfig struct {
	Keyword         string
	PaddingPRNGSeed *prng.Seed
	MinPadding      *int
	MaxPadding      *int

	SeedHistory       *SeedHistory
	StrictHistoryMode bool
	IrregularLogger   func(clientIP string, err error, logFields common.LogFields)
}

ObfuscatorConfig specifies an Obfuscator configuration.

type SeedHistory

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

SeedHistory maintains a history of recently observed obfuscation seed values. This history is used to identify duplicate seed messages.

As a heurististic to exclude expected duplicates, due to, for example, meek retries, the source client IP is retained for comparison for a short duration -- long enough to cover meek retries without retaining client IPs in memory long past a client connection lifetime.

func NewSeedHistory

func NewSeedHistory(config *SeedHistoryConfig) *SeedHistory

NewSeedHistory creates a new SeedHistory. Config is optional.

func (*SeedHistory) AddNew

func (h *SeedHistory) AddNew(
	strictMode bool,
	clientIP string,
	seedType string,
	seed []byte) (bool, *common.LogFields)

AddNew adds a new seed value to the history. If the seed value is already in the history, and an expected case such as a meek retry is ruled out (or strictMode is on), AddNew returns false.

When a duplicate seed is found, a common.LogFields instance is returned, populated with event data. Log fields may be returned in either the false or true case.

type SeedHistoryConfig

type SeedHistoryConfig struct {
	SeedTTL            time.Duration
	SeedMaxEntries     int
	ClientIPTTL        time.Duration
	ClientIPMaxEntries int
}