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443 lines
13 KiB
443 lines
13 KiB
package conn
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import (
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"bytes"
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"crypto/cipher"
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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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"fmt"
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"io"
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"math"
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"net"
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"sync"
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"time"
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"github.com/gtank/merlin"
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pool "github.com/libp2p/go-buffer-pool"
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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/hkdf"
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"golang.org/x/crypto/nacl/box"
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"github.com/tendermint/tendermint/crypto"
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"github.com/tendermint/tendermint/crypto/ed25519"
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"github.com/tendermint/tendermint/libs/async"
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)
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// 4 + 1024 == 1028 total frame size
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const (
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dataLenSize = 4
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dataMaxSize = 1024
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totalFrameSize = dataMaxSize + dataLenSize
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aeadSizeOverhead = 16 // overhead of poly 1305 authentication tag
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aeadKeySize = chacha20poly1305.KeySize
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aeadNonceSize = chacha20poly1305.NonceSize
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)
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var (
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ErrSmallOrderRemotePubKey = errors.New("detected low order point from remote peer")
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labelEphemeralLowerPublicKey = []byte("EPHEMERAL_LOWER_PUBLIC_KEY")
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labelEphemeralUpperPublicKey = []byte("EPHEMERAL_UPPER_PUBLIC_KEY")
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labelDHSecret = []byte("DH_SECRET")
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labelSecretConnectionMac = []byte("SECRET_CONNECTION_MAC")
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secretConnKeyAndChallengeGen = []byte("TENDERMINT_SECRET_CONNECTION_KEY_AND_CHALLENGE_GEN")
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)
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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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recvAead cipher.AEAD
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sendAead cipher.AEAD
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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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var (
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locPubKey = locPrivKey.PubKey()
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)
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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 (see
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// 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, hiEphPub := sort32(locEphPub, remEphPub)
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transcript := merlin.NewTranscript("TENDERMINT_SECRET_CONNECTION_TRANSCRIPT_HASH")
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transcript.AppendMessage(labelEphemeralLowerPublicKey, loEphPub[:])
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transcript.AppendMessage(labelEphemeralUpperPublicKey, hiEphPub[:])
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// Check if the local ephemeral public key was the least, lexicographically
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// 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, err := computeDHSecret(remEphPub, locEphPriv)
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if err != nil {
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return nil, err
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}
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transcript.AppendMessage(labelDHSecret, dhSecret[:])
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// Generate the secret used for receiving, sending, challenge via HKDF-SHA2
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// on the transcript state (which itself also uses HKDF-SHA2 to derive a key
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// from the dhSecret).
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recvSecret, sendSecret := deriveSecrets(dhSecret, locIsLeast)
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const challengeSize = 32
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var challenge [challengeSize]byte
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challengeSlice := transcript.ExtractBytes(labelSecretConnectionMac, challengeSize)
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copy(challenge[:], challengeSlice[0:challengeSize])
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sendAead, err := chacha20poly1305.New(sendSecret[:])
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if err != nil {
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return nil, errors.New("invalid send SecretConnection Key")
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}
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recvAead, err := chacha20poly1305.New(recvSecret[:])
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if err != nil {
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return nil, errors.New("invalid receive SecretConnection Key")
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}
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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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recvAead: recvAead,
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sendAead: sendAead,
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}
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// Sign the challenge bytes for authentication.
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locSignature, err := signChallenge(&challenge, locPrivKey)
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if err != nil {
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return nil, err
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}
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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 _, ok := remPubKey.(ed25519.PubKey); !ok {
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return nil, fmt.Errorf("expected ed25519 pubkey, got %T", remPubKey)
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}
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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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if err := func() error {
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var sealedFrame = pool.Get(aeadSizeOverhead + totalFrameSize)
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var frame = pool.Get(totalFrameSize)
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defer func() {
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pool.Put(sealedFrame)
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pool.Put(frame)
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}()
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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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// encrypt the frame
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sc.sendAead.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 err
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}
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n += len(chunk)
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return nil
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}(); err != nil {
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return n, err
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}
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}
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return n, err
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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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var sealedFrame = pool.Get(aeadSizeOverhead + totalFrameSize)
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defer pool.Put(sealedFrame)
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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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// reads and updates the sc.recvNonce
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var frame = pool.Get(totalFrameSize)
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defer pool.Put(frame)
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_, err = sc.recvAead.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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if n < len(chunk) {
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sc.recvBuffer = make([]byte, len(chunk)-n)
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copy(sc.recvBuffer, chunk[n:])
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}
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return n, err
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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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// TODO: Probably not a problem but ask Tony: different from the rust implementation (uses x25519-dalek),
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// we do not "clamp" the private key scalar:
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// see: https://github.com/dalek-cryptography/x25519-dalek/blob/34676d336049df2bba763cc076a75e47ae1f170f/src/x25519.rs#L56-L74
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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 key-pair")
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}
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return
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}
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func shareEphPubKey(conn io.ReadWriter, 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, _ = async.Parallel(
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func(_ int) (val interface{}, abort bool, err error) {
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var _, err1 = cdc.MarshalBinaryLengthPrefixedWriter(conn, locEphPub)
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if err1 != nil {
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return nil, true, err1 // abort
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}
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return nil, false, nil
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},
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func(_ int) (val interface{}, abort bool, err error) {
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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, true, err2 // abort
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}
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return _remEphPub, false, nil
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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 deriveSecrets(
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dhSecret *[32]byte,
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locIsLeast bool,
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) (recvSecret, sendSecret *[aeadKeySize]byte) {
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hash := sha256.New
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hkdf := hkdf.New(hash, dhSecret[:], nil, secretConnKeyAndChallengeGen)
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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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recvSecret = new([aeadKeySize]byte)
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sendSecret = new([aeadKeySize]byte)
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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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// computeDHSecret computes a Diffie-Hellman shared secret key
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// from our own local private key and the other's public key.
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func computeDHSecret(remPubKey, locPrivKey *[32]byte) (*[32]byte, error) {
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shrKey, err := curve25519.X25519(locPrivKey[:], remPubKey[:])
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if err != nil {
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return nil, err
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}
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var shrKeyArray [32]byte
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copy(shrKeyArray[:], shrKey)
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return &shrKeyArray, nil
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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) ([]byte, error) {
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signature, err := locPrivKey.Sign(challenge[:])
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if err != nil {
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return nil, err
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}
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return signature, nil
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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 io.ReadWriter, 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, _ = async.Parallel(
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func(_ int) (val interface{}, abort bool, err error) {
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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, true, err1 // abort
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}
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return nil, false, nil
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},
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func(_ int) (val interface{}, abort bool, err error) {
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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, true, err2 // abort
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}
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return _recvMsg, false, nil
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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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if counter == math.MaxUint64 {
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// Terminates the session and makes sure the nonce would not re-used.
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// See https://github.com/tendermint/tendermint/issues/3531
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panic("can't increase nonce without overflow")
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}
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counter++
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binary.LittleEndian.PutUint64(nonce[4:], counter)
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}
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