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350 lines
9.3 KiB
350 lines
9.3 KiB
// Uses nacl's secret_box to encrypt a net.Conn.
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// It is (meant to be) an implementation of the STS protocol.
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// Note we do not (yet) assume that a remote peer's pubkey
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// is known ahead of time, and thus we are technically
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// still vulnerable to MITM. (TODO!)
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// See docs/sts-final.pdf for more info
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package conn
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import (
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"bytes"
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crand "crypto/rand"
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"crypto/sha256"
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"encoding/binary"
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"errors"
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"io"
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"net"
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"time"
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"golang.org/x/crypto/nacl/box"
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"golang.org/x/crypto/nacl/secretbox"
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"golang.org/x/crypto/ripemd160"
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"github.com/tendermint/go-crypto"
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cmn "github.com/tendermint/tmlibs/common"
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)
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// 4 + 1024 == 1028 total frame size
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const dataLenSize = 4
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const dataMaxSize = 1024
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const totalFrameSize = dataMaxSize + dataLenSize
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const sealedFrameSize = totalFrameSize + secretbox.Overhead
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// Implements net.Conn
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type SecretConnection struct {
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conn io.ReadWriteCloser
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recvBuffer []byte
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recvNonce *[24]byte
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sendNonce *[24]byte
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remPubKey crypto.PubKey
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shrSecret *[32]byte // shared secret
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}
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// Performs handshake and returns a new authenticated SecretConnection.
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// Returns nil if error in handshake.
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// Caller should call conn.Close()
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// See docs/sts-final.pdf for more information.
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func MakeSecretConnection(conn io.ReadWriteCloser, locPrivKey crypto.PrivKey) (*SecretConnection, error) {
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locPubKey := locPrivKey.PubKey()
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// Generate ephemeral keys for perfect forward secrecy.
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locEphPub, locEphPriv := genEphKeys()
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// Write local ephemeral pubkey and receive one too.
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// NOTE: every 32-byte string is accepted as a Curve25519 public key
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// (see DJB's Curve25519 paper: http://cr.yp.to/ecdh/curve25519-20060209.pdf)
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remEphPub, err := shareEphPubKey(conn, locEphPub)
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if err != nil {
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return nil, err
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}
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// Compute common shared secret.
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shrSecret := computeSharedSecret(remEphPub, locEphPriv)
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// Sort by lexical order.
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loEphPub, hiEphPub := sort32(locEphPub, remEphPub)
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// Check if the local ephemeral public key
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// was the least, lexicographically sorted.
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locIsLeast := bytes.Equal(locEphPub[:], loEphPub[:])
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// Generate nonces to use for secretbox.
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recvNonce, sendNonce := genNonces(loEphPub, hiEphPub, locIsLeast)
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// Generate common challenge to sign.
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challenge := genChallenge(loEphPub, hiEphPub)
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// Construct SecretConnection.
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sc := &SecretConnection{
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conn: conn,
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recvBuffer: nil,
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recvNonce: recvNonce,
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sendNonce: sendNonce,
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shrSecret: shrSecret,
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}
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// Sign the challenge bytes for authentication.
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locSignature := signChallenge(challenge, locPrivKey)
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// Share (in secret) each other's pubkey & challenge signature
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authSigMsg, err := shareAuthSignature(sc, locPubKey, locSignature)
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if err != nil {
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return nil, err
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}
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remPubKey, remSignature := authSigMsg.Key, authSigMsg.Sig
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if !remPubKey.VerifyBytes(challenge[:], remSignature) {
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return nil, errors.New("Challenge verification failed")
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}
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// We've authorized.
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sc.remPubKey = remPubKey
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return sc, nil
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}
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// Returns authenticated remote pubkey
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func (sc *SecretConnection) RemotePubKey() crypto.PubKey {
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return sc.remPubKey
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}
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// Writes encrypted frames of `sealedFrameSize`
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// CONTRACT: data smaller than dataMaxSize is read atomically.
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func (sc *SecretConnection) Write(data []byte) (n int, err error) {
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for 0 < len(data) {
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var frame []byte = make([]byte, totalFrameSize)
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var chunk []byte
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if dataMaxSize < len(data) {
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chunk = data[:dataMaxSize]
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data = data[dataMaxSize:]
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} else {
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chunk = data
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data = nil
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}
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chunkLength := len(chunk)
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binary.BigEndian.PutUint32(frame, uint32(chunkLength))
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copy(frame[dataLenSize:], chunk)
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// encrypt the frame
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var sealedFrame = make([]byte, sealedFrameSize)
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secretbox.Seal(sealedFrame[:0], frame, sc.sendNonce, sc.shrSecret)
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// fmt.Printf("secretbox.Seal(sealed:%X,sendNonce:%X,shrSecret:%X\n", sealedFrame, sc.sendNonce, sc.shrSecret)
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incr2Nonce(sc.sendNonce)
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// end encryption
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_, err := sc.conn.Write(sealedFrame)
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if err != nil {
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return n, err
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} else {
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n += len(chunk)
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}
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}
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return
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}
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// CONTRACT: data smaller than dataMaxSize is read atomically.
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func (sc *SecretConnection) Read(data []byte) (n int, err error) {
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if 0 < len(sc.recvBuffer) {
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n = copy(data, sc.recvBuffer)
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sc.recvBuffer = sc.recvBuffer[n:]
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return
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}
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sealedFrame := make([]byte, sealedFrameSize)
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_, err = io.ReadFull(sc.conn, sealedFrame)
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if err != nil {
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return
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}
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// decrypt the frame
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var frame = make([]byte, totalFrameSize)
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// fmt.Printf("secretbox.Open(sealed:%X,recvNonce:%X,shrSecret:%X\n", sealedFrame, sc.recvNonce, sc.shrSecret)
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_, ok := secretbox.Open(frame[:0], sealedFrame, sc.recvNonce, sc.shrSecret)
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if !ok {
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return n, errors.New("Failed to decrypt SecretConnection")
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}
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incr2Nonce(sc.recvNonce)
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// end decryption
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var chunkLength = binary.BigEndian.Uint32(frame) // read the first two bytes
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if chunkLength > dataMaxSize {
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return 0, errors.New("chunkLength is greater than dataMaxSize")
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}
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var chunk = frame[dataLenSize : dataLenSize+chunkLength]
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n = copy(data, chunk)
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sc.recvBuffer = chunk[n:]
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return
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}
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// Implements net.Conn
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func (sc *SecretConnection) Close() error { return sc.conn.Close() }
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func (sc *SecretConnection) LocalAddr() net.Addr { return sc.conn.(net.Conn).LocalAddr() }
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func (sc *SecretConnection) RemoteAddr() net.Addr { return sc.conn.(net.Conn).RemoteAddr() }
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func (sc *SecretConnection) SetDeadline(t time.Time) error { return sc.conn.(net.Conn).SetDeadline(t) }
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func (sc *SecretConnection) SetReadDeadline(t time.Time) error {
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return sc.conn.(net.Conn).SetReadDeadline(t)
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}
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func (sc *SecretConnection) SetWriteDeadline(t time.Time) error {
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return sc.conn.(net.Conn).SetWriteDeadline(t)
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}
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func genEphKeys() (ephPub, ephPriv *[32]byte) {
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var err error
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ephPub, ephPriv, err = box.GenerateKey(crand.Reader)
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if err != nil {
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panic("Could not generate ephemeral keypairs")
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}
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return
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}
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func shareEphPubKey(conn io.ReadWriteCloser, locEphPub *[32]byte) (remEphPub *[32]byte, err error) {
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// Send our pubkey and receive theirs in tandem.
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var trs, _ = cmn.Parallel(
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func(_ int) (val interface{}, err error, abort bool) {
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var _, err1 = cdc.MarshalBinaryWriter(conn, locEphPub)
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if err1 != nil {
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return nil, err1, true // abort
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} else {
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return nil, nil, false
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}
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},
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func(_ int) (val interface{}, err error, abort bool) {
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var _remEphPub [32]byte
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var _, err2 = cdc.UnmarshalBinaryReader(conn, &_remEphPub, 1024*1024) // TODO
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if err2 != nil {
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return nil, err2, true // abort
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} else {
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return _remEphPub, nil, false
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}
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},
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)
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// If error:
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if trs.FirstError() != nil {
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err = trs.FirstError()
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return
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}
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// Otherwise:
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var _remEphPub = trs.FirstValue().([32]byte)
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return &_remEphPub, nil
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}
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func computeSharedSecret(remPubKey, locPrivKey *[32]byte) (shrSecret *[32]byte) {
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shrSecret = new([32]byte)
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box.Precompute(shrSecret, remPubKey, locPrivKey)
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return
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}
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func sort32(foo, bar *[32]byte) (lo, hi *[32]byte) {
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if bytes.Compare(foo[:], bar[:]) < 0 {
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lo = foo
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hi = bar
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} else {
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lo = bar
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hi = foo
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}
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return
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}
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func genNonces(loPubKey, hiPubKey *[32]byte, locIsLo bool) (recvNonce, sendNonce *[24]byte) {
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nonce1 := hash24(append(loPubKey[:], hiPubKey[:]...))
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nonce2 := new([24]byte)
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copy(nonce2[:], nonce1[:])
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nonce2[len(nonce2)-1] ^= 0x01
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if locIsLo {
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recvNonce = nonce1
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sendNonce = nonce2
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} else {
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recvNonce = nonce2
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sendNonce = nonce1
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}
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return
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}
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func genChallenge(loPubKey, hiPubKey *[32]byte) (challenge *[32]byte) {
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return hash32(append(loPubKey[:], hiPubKey[:]...))
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}
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func signChallenge(challenge *[32]byte, locPrivKey crypto.PrivKey) (signature crypto.Signature) {
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signature = locPrivKey.Sign(challenge[:])
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return
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}
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type authSigMessage struct {
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Key crypto.PubKey
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Sig crypto.Signature
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}
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func shareAuthSignature(sc *SecretConnection, pubKey crypto.PubKey, signature crypto.Signature) (recvMsg authSigMessage, err error) {
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// Send our info and receive theirs in tandem.
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var trs, _ = cmn.Parallel(
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func(_ int) (val interface{}, err error, abort bool) {
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var _, err1 = cdc.MarshalBinaryWriter(sc, authSigMessage{pubKey, signature})
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if err1 != nil {
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return nil, err1, true // abort
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} else {
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return nil, nil, false
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}
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},
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func(_ int) (val interface{}, err error, abort bool) {
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var _recvMsg authSigMessage
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var _, err2 = cdc.UnmarshalBinaryReader(sc, &_recvMsg, 1024*1024) // TODO
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if err2 != nil {
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return nil, err2, true // abort
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} else {
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return _recvMsg, nil, false
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}
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},
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)
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// If error:
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if trs.FirstError() != nil {
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err = trs.FirstError()
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return
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}
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var _recvMsg = trs.FirstValue().(authSigMessage)
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return _recvMsg, nil
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}
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//--------------------------------------------------------------------------------
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// sha256
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func hash32(input []byte) (res *[32]byte) {
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hasher := sha256.New()
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hasher.Write(input) // nolint: errcheck, gas
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resSlice := hasher.Sum(nil)
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res = new([32]byte)
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copy(res[:], resSlice)
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return
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}
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// We only fill in the first 20 bytes with ripemd160
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func hash24(input []byte) (res *[24]byte) {
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hasher := ripemd160.New()
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hasher.Write(input) // nolint: errcheck, gas
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resSlice := hasher.Sum(nil)
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res = new([24]byte)
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copy(res[:], resSlice)
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return
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}
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// increment nonce big-endian by 2 with wraparound.
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func incr2Nonce(nonce *[24]byte) {
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incrNonce(nonce)
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incrNonce(nonce)
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}
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// increment nonce big-endian by 1 with wraparound.
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func incrNonce(nonce *[24]byte) {
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for i := 23; 0 <= i; i-- {
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nonce[i] += 1
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if nonce[i] != 0 {
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return
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}
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}
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}
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