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424 lines
13 KiB
424 lines
13 KiB
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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"crypto/subtle"
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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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"sync"
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"time"
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"golang.org/x/crypto/chacha20poly1305"
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"golang.org/x/crypto/curve25519"
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"golang.org/x/crypto/nacl/box"
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"github.com/tendermint/tendermint/crypto"
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cmn "github.com/tendermint/tendermint/libs/common"
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"golang.org/x/crypto/hkdf"
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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 aeadSizeOverhead = 16 // overhead of poly 1305 authentication tag
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const aeadKeySize = chacha20poly1305.KeySize
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const aeadNonceSize = chacha20poly1305.NonceSize
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var ErrSmallOrderRemotePubKey = errors.New("detected low order point from remote peer")
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// SecretConnection implements net.Conn.
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// It is an implementation of the STS protocol.
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// See https://github.com/tendermint/tendermint/blob/0.1/docs/sts-final.pdf for
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// details on the protocol.
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//
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// Consumers of the SecretConnection are responsible for authenticating
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// the remote peer's pubkey against known information, like a nodeID.
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// Otherwise they are vulnerable to MITM.
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// (TODO(ismail): see also https://github.com/tendermint/tendermint/issues/3010)
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type SecretConnection struct {
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// immutable
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recvSecret *[aeadKeySize]byte
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sendSecret *[aeadKeySize]byte
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remPubKey crypto.PubKey
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conn io.ReadWriteCloser
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// net.Conn must be thread safe:
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// https://golang.org/pkg/net/#Conn.
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// Since we have internal mutable state,
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// we need mtxs. But recv and send states
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// are independent, so we can use two mtxs.
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// All .Read are covered by recvMtx,
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// all .Write are covered by sendMtx.
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recvMtx sync.Mutex
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recvBuffer []byte
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recvNonce *[aeadNonceSize]byte
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sendMtx sync.Mutex
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sendNonce *[aeadNonceSize]byte
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}
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// MakeSecretConnection performs handshake and returns a new authenticated
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// SecretConnection.
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// Returns nil if there is an 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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// Sort by lexical order.
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loEphPub, _ := 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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// Compute common diffie hellman secret using X25519.
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dhSecret := computeDHSecret(remEphPub, locEphPriv)
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// generate the secret used for receiving, sending, challenge via hkdf-sha2 on dhSecret
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recvSecret, sendSecret, challenge := deriveSecretAndChallenge(dhSecret, locIsLeast)
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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: new([aeadNonceSize]byte),
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sendNonce: new([aeadNonceSize]byte),
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recvSecret: recvSecret,
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sendSecret: sendSecret,
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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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// RemotePubKey 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 `totalFrameSize + aeadSizeOverhead`.
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// CONTRACT: data smaller than dataMaxSize is written atomically.
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func (sc *SecretConnection) Write(data []byte) (n int, err error) {
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sc.sendMtx.Lock()
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defer sc.sendMtx.Unlock()
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for 0 < len(data) {
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var frame = 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.LittleEndian.PutUint32(frame, uint32(chunkLength))
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copy(frame[dataLenSize:], chunk)
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aead, err := chacha20poly1305.New(sc.sendSecret[:])
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if err != nil {
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return n, errors.New("Invalid SecretConnection Key")
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}
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// encrypt the frame
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var sealedFrame = make([]byte, aeadSizeOverhead+totalFrameSize)
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aead.Seal(sealedFrame[:0], sc.sendNonce[:], frame, nil)
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incrNonce(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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}
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n += len(chunk)
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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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sc.recvMtx.Lock()
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defer sc.recvMtx.Unlock()
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// read off and update the recvBuffer, if non-empty
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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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// read off the conn
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sealedFrame := make([]byte, totalFrameSize+aeadSizeOverhead)
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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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aead, err := chacha20poly1305.New(sc.recvSecret[:])
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if err != nil {
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return n, errors.New("Invalid SecretConnection Key")
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}
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// decrypt the frame.
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// reads and updates the sc.recvNonce
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var frame = make([]byte, totalFrameSize)
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_, err = aead.Open(frame[:0], sc.recvNonce[:], sealedFrame, nil)
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if err != nil {
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return n, errors.New("Failed to decrypt SecretConnection")
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}
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incrNonce(sc.recvNonce)
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// end decryption
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// copy checkLength worth into data,
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// set recvBuffer to the rest.
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var chunkLength = binary.LittleEndian.Uint32(frame) // read the first four 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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// nolint
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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.MarshalBinaryLengthPrefixedWriter(conn, locEphPub)
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if err1 != nil {
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return nil, err1, true // abort
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}
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return nil, nil, false
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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.UnmarshalBinaryLengthPrefixedReader(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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}
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if hasSmallOrder(_remEphPub) {
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return nil, ErrSmallOrderRemotePubKey, true
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}
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return _remEphPub, nil, false
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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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// use the samne blacklist as lib sodium (see https://eprint.iacr.org/2017/806.pdf for reference):
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// https://github.com/jedisct1/libsodium/blob/536ed00d2c5e0c65ac01e29141d69a30455f2038/src/libsodium/crypto_scalarmult/curve25519/ref10/x25519_ref10.c#L11-L17
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var blacklist = [][32]byte{
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// 0 (order 4)
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{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
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// 1 (order 1)
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{0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
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// 325606250916557431795983626356110631294008115727848805560023387167927233504
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// (order 8)
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{0xe0, 0xeb, 0x7a, 0x7c, 0x3b, 0x41, 0xb8, 0xae, 0x16, 0x56, 0xe3,
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0xfa, 0xf1, 0x9f, 0xc4, 0x6a, 0xda, 0x09, 0x8d, 0xeb, 0x9c, 0x32,
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0xb1, 0xfd, 0x86, 0x62, 0x05, 0x16, 0x5f, 0x49, 0xb8, 0x00},
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// 39382357235489614581723060781553021112529911719440698176882885853963445705823
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// (order 8)
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{0x5f, 0x9c, 0x95, 0xbc, 0xa3, 0x50, 0x8c, 0x24, 0xb1, 0xd0, 0xb1,
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0x55, 0x9c, 0x83, 0xef, 0x5b, 0x04, 0x44, 0x5c, 0xc4, 0x58, 0x1c,
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0x8e, 0x86, 0xd8, 0x22, 0x4e, 0xdd, 0xd0, 0x9f, 0x11, 0x57},
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// p-1 (order 2)
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{0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f},
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// p (=0, order 4)
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{0xed, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f},
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// p+1 (=1, order 1)
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{0xee, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f},
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}
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func hasSmallOrder(pubKey [32]byte) bool {
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isSmallOrderPoint := false
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for _, bl := range blacklist {
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if subtle.ConstantTimeCompare(pubKey[:], bl[:]) == 1 {
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isSmallOrderPoint = true
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break
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}
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}
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return isSmallOrderPoint
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}
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func deriveSecretAndChallenge(dhSecret *[32]byte, locIsLeast bool) (recvSecret, sendSecret *[aeadKeySize]byte, challenge *[32]byte) {
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hash := sha256.New
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hkdf := hkdf.New(hash, dhSecret[:], nil, []byte("TENDERMINT_SECRET_CONNECTION_KEY_AND_CHALLENGE_GEN"))
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// get enough data for 2 aead keys, and a 32 byte challenge
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res := new([2*aeadKeySize + 32]byte)
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_, err := io.ReadFull(hkdf, res[:])
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if err != nil {
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panic(err)
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}
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challenge = new([32]byte)
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recvSecret = new([aeadKeySize]byte)
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sendSecret = new([aeadKeySize]byte)
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// Use the last 32 bytes as the challenge
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copy(challenge[:], res[2*aeadKeySize:2*aeadKeySize+32])
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// bytes 0 through aeadKeySize - 1 are one aead key.
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// bytes aeadKeySize through 2*aeadKeySize -1 are another aead key.
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// which key corresponds to sending and receiving key depends on whether
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// the local key is less than the remote key.
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if locIsLeast {
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copy(recvSecret[:], res[0:aeadKeySize])
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copy(sendSecret[:], res[aeadKeySize:aeadKeySize*2])
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} else {
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copy(sendSecret[:], res[0:aeadKeySize])
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copy(recvSecret[:], res[aeadKeySize:aeadKeySize*2])
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}
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return
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}
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func computeDHSecret(remPubKey, locPrivKey *[32]byte) (shrKey *[32]byte) {
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shrKey = new([32]byte)
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curve25519.ScalarMult(shrKey, locPrivKey, remPubKey)
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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 signChallenge(challenge *[32]byte, locPrivKey crypto.PrivKey) (signature []byte) {
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signature, err := locPrivKey.Sign(challenge[:])
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// TODO(ismail): let signChallenge return an error instead
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if err != nil {
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panic(err)
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}
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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 []byte
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}
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func shareAuthSignature(sc *SecretConnection, pubKey crypto.PubKey, signature []byte) (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.MarshalBinaryLengthPrefixedWriter(sc, authSigMessage{pubKey, signature})
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if err1 != nil {
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return nil, err1, true // abort
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}
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return nil, nil, false
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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.UnmarshalBinaryLengthPrefixedReader(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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}
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return _recvMsg, nil, false
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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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// Increment nonce little-endian by 1 with wraparound.
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// Due to chacha20poly1305 expecting a 12 byte nonce we do not use the first four
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// bytes. We only increment a 64 bit unsigned int in the remaining 8 bytes
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// (little-endian in nonce[4:]).
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func incrNonce(nonce *[aeadNonceSize]byte) {
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counter := binary.LittleEndian.Uint64(nonce[4:])
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counter++
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binary.LittleEndian.PutUint64(nonce[4:], counter)
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}
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