watchtower/blob/justice_kit: adds v0 encoding and encryption
This commit is contained in:
Conner Fromknecht
Conner Fromknecht
parent
b0379dfa59
commit
9749096403
442
watchtower/blob/justice_kit.go
Normal file
442
watchtower/blob/justice_kit.go
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@ -0,0 +1,442 @@
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package blob
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import (
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"bytes"
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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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"golang.org/x/crypto/chacha20poly1305"
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"github.com/btcsuite/btcd/btcec"
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"github.com/btcsuite/btcd/txscript"
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"github.com/lightningnetwork/lnd/lnwallet"
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"github.com/lightningnetwork/lnd/lnwire"
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)
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const (
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// MinVersion is the minimum blob version supported by this package.
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MinVersion = 0
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// MaxVersion is the maximumm blob version supported by this package.
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MaxVersion = 0
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// NonceSize is the length of a chacha20poly1305 nonce, 12 bytes.
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NonceSize = chacha20poly1305.NonceSize
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// KeySize is the length of a chacha20poly1305 key, 32 bytes.
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KeySize = chacha20poly1305.KeySize
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// CiphertextExpansion is the number of bytes padded to a plaintext
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// encrypted with chacha20poly1305, which comes from a 16-byte MAC.
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CiphertextExpansion = 16
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// V0PlaintextSize is the plaintext size of a version 0 encoded blob.
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// sweep address: 42 bytes
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// revocation pubkey: 33 bytes
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// local delay pubkey: 33 bytes
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// csv delay: 4 bytes
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// commit to-local revocation sig: 64 bytes
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// commit to-remote pubkey: 33 bytes, maybe blank
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// commit to-remote sig: 64 bytes, maybe blank
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V0PlaintextSize = 273
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)
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// Size returns the size of the encoded-and-encrypted blob in bytes.
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// enciphered plaintext: n bytes
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// MAC: 16 bytes
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func Size(ver uint16) int {
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return PlaintextSize(ver) + CiphertextExpansion
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}
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// PlaintextSize returns the size of the encoded-but-unencrypted blob in bytes.
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func PlaintextSize(ver uint16) int {
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switch ver {
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case 0:
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return V0PlaintextSize
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default:
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return 0
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}
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}
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var (
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// byteOrder specifies a big-endian encoding of all integer values.
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byteOrder = binary.BigEndian
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// ErrUnknownBlobVersion signals that we don't understand the requested
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// blob encoding scheme.
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ErrUnknownBlobVersion = errors.New("unknown blob version")
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// ErrCiphertextTooSmall is a decryption error signaling that the
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// ciphertext is smaller than the ciphertext expansion factor.
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ErrCiphertextTooSmall = errors.New(
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"ciphertext is too small for chacha20poly1305",
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)
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// ErrNonceSize signals that the provided nonce is improperly sized.
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ErrNonceSize = fmt.Errorf(
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"chacha20poly1305 nonce must be %d bytes", NonceSize,
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)
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// ErrKeySize signals that the provided key is improperly sized.
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ErrKeySize = fmt.Errorf(
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"chacha20poly1305 key size must be %d bytes", KeySize,
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)
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// ErrNoCommitToRemoteOutput is returned when trying to retrieve the
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// commit to-remote output from the blob, though none exists.
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ErrNoCommitToRemoteOutput = errors.New(
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"cannot obtain commit to-remote p2wkh output script from blob",
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)
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)
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// PubKey is a 33-byte, serialized compressed public key.
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type PubKey [33]byte
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// JusticeKit is lé Blob of Justice. The JusticeKit contains information
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// required to construct a justice transaction, that sweeps a remote party's
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// revoked commitment transaction. It supports encryption and decryption using
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// chacha20poly1305, allowing the client to encrypt the contents of the blob,
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// and for a watchtower to later decrypt if action must be taken. The encoding
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// format is versioned to allow future extensions.
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type JusticeKit struct {
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// SweepAddress is the witness program of the output where the client's
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// fund will be deposited. This value is included in the blobs, as
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// opposed to the session info, such that the sweep addresses can't be
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// correlated across sessions and/or towers.
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//
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// NOTE: This is chosen to be the length of a maximally sized witness
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// program.
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SweepAddress [42]byte
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// RevocationPubKey is the compressed pubkey that guards the revocation
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// clause of the remote party's to-local output.
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RevocationPubKey PubKey
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// LocalDelayPubKey is the compressed pubkey in the to-local script of
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// the remote party, which guards the path where the remote party
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// claims their commitment output.
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LocalDelayPubKey PubKey
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// CSVDelay is the relative timelock in the remote party's to-local
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// output, which the remote party must wait out before sweeping their
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// commitment output.
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CSVDelay uint32
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// CommitToLocalSig is a signature under RevocationPubKey using
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// SIGHASH_ALL.
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CommitToLocalSig lnwire.Sig
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// CommitToRemotePubKey is the public key in the to-remote output of the revoked
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// commitment transaction.
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//
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// NOTE: This value is only used if it contains a valid compressed
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// public key.
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CommitToRemotePubKey PubKey
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// CommitToRemoteSig is a signature under CommitToRemotePubKey using SIGHASH_ALL.
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//
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// NOTE: This value is only used if CommitToRemotePubKey contains a valid
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// compressed public key.
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CommitToRemoteSig lnwire.Sig
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}
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// CommitToLocalWitnessScript returns the serialized witness script for the
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// commitment to-local output.
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func (b *JusticeKit) CommitToLocalWitnessScript() ([]byte, error) {
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revocationPubKey, err := btcec.ParsePubKey(
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b.RevocationPubKey[:], btcec.S256(),
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)
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if err != nil {
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return nil, err
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}
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localDelayedPubKey, err := btcec.ParsePubKey(
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b.LocalDelayPubKey[:], btcec.S256(),
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)
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if err != nil {
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return nil, err
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}
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return lnwallet.CommitScriptToSelf(
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b.CSVDelay, localDelayedPubKey, revocationPubKey,
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)
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}
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// CommitToLocalRevokeWitnessStack constructs a witness stack spending the
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// revocation clause of the commitment to-local output.
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// <revocation-sig> 1
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func (b *JusticeKit) CommitToLocalRevokeWitnessStack() [][]byte {
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witnessStack := make([][]byte, 2)
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witnessStack[0] = append(b.CommitToLocalSig[:], byte(txscript.SigHashAll))
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witnessStack[1] = []byte{1}
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return witnessStack
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}
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// HasCommitToRemoteOutput returns true if the blob contains a to-remote p2wkh
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// pubkey.
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func (b *JusticeKit) HasCommitToRemoteOutput() bool {
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return btcec.IsCompressedPubKey(b.CommitToRemotePubKey[:])
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}
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// CommitToRemoteWitnessScript returns the witness script for the commitment
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// to-remote p2wkh output, which is the pubkey itself.
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func (b *JusticeKit) CommitToRemoteWitnessScript() ([]byte, error) {
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if !btcec.IsCompressedPubKey(b.CommitToRemotePubKey[:]) {
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return nil, ErrNoCommitToRemoteOutput
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}
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return b.CommitToRemotePubKey[:], nil
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}
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// CommitToRemoteWitnessStack returns a witness stack spending the commitment
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// to-remote output, which is a regular p2wkh.
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// <to-remote-sig>
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func (b *JusticeKit) CommitToRemoteWitnessStack() [][]byte {
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witnessStack := make([][]byte, 1)
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witnessStack[0] = append(b.CommitToRemoteSig[:], byte(txscript.SigHashAll))
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return witnessStack
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}
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// Encrypt encodes the blob of justice using encoding version, and then
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// creates a ciphertext using chacha20poly1305 under the chosen (nonce, key)
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// pair.
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//
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// NOTE: It is the caller's responsibility to ensure that this method is only
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// called once for a given (nonce, key) pair.
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func (b *JusticeKit) Encrypt(nonce, key []byte, version uint16) ([]byte, error) {
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switch {
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// Fail if the nonce is not 12-bytes.
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case len(nonce) != NonceSize:
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return nil, ErrNonceSize
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// Fail if the nonce is not 32-bytes.
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case len(key) != KeySize:
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return nil, ErrKeySize
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}
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// Encode the plaintext using the provided version, to obtain the
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// plaintext bytes.
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var ptxtBuf bytes.Buffer
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err := b.encode(&ptxtBuf, version)
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if err != nil {
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return nil, err
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}
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// Create a new chacha20poly1305 cipher, using a 32-byte key.
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cipher, err := chacha20poly1305.New(key)
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if err != nil {
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return nil, err
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}
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// Allocate the ciphertext, which will contain the encrypted plaintext
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// and MAC.
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plaintext := ptxtBuf.Bytes()
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ciphertext := make([]byte, len(plaintext)+CiphertextExpansion)
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// Finally, encrypt the plaintext using the given nonce, storing the
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// result in the ciphertext buffer.
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cipher.Seal(ciphertext[:0], nonce, plaintext, nil)
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return ciphertext, nil
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}
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// Decrypt unenciphers a blob of justice by decrypting the ciphertext using
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// chacha20poly1305 with the chosen (nonce, key) pair. The internal plaintext is
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// then deserialized using the given encoding version.
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func Decrypt(nonce, key, ciphertext []byte, version uint16) (*JusticeKit, error) {
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switch {
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// Fail if the blob's overall length is less than the expansion factor.
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case len(ciphertext) < CiphertextExpansion:
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return nil, ErrCiphertextTooSmall
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// Fail if the nonce is not 12-bytes.
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case len(nonce) != NonceSize:
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return nil, ErrNonceSize
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// Fail if the key is not 32-bytes.
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case len(key) != KeySize:
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return nil, ErrKeySize
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}
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// Create a new chacha20poly1305 cipher, using a 32-byte key.
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cipher, err := chacha20poly1305.New(key)
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if err != nil {
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return nil, err
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}
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// Allocate the final buffer that will contain the blob's plaintext
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// bytes, which is computed by subtracting the ciphertext expansion
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// factor from the blob's length.
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plaintext := make([]byte, len(ciphertext)-CiphertextExpansion)
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// Decrypt the ciphertext, placing the resulting plaintext in our
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// plaintext buffer.
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_, err = cipher.Open(plaintext[:0], nonce, ciphertext, nil)
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if err != nil {
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return nil, err
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}
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// If decryption succeeded, we will then decode the plaintext bytes
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// using the specified blob version.
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boj := &JusticeKit{}
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err = boj.decode(bytes.NewReader(plaintext), version)
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if err != nil {
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return nil, err
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}
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return boj, nil
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}
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// encode serializes the JusticeKit according to the version, returning an
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// error if the version is unknown.
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func (b *JusticeKit) encode(w io.Writer, ver uint16) error {
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switch ver {
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case 0:
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return b.encodeV0(w)
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default:
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return ErrUnknownBlobVersion
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}
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}
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// decode deserializes the JusticeKit according to the version, returning an
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// error if the version is unknown.
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func (b *JusticeKit) decode(r io.Reader, ver uint16) error {
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switch ver {
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case 0:
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return b.decodeV0(r)
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default:
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return ErrUnknownBlobVersion
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}
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}
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// encodeV0 encodes the JusticeKit using the version 0 encoding scheme to the
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// provided io.Writer. The encoding supports sweeping of the commit to-local
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// output, and optionally the commit to-remote output. The encoding produces a
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// constant-size plaintext size of 273 bytes.
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//
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// blob version 0 plaintext encoding:
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// sweep address: 42 bytes
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// revocation pubkey: 33 bytes
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// local delay pubkey: 33 bytes
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// csv delay: 4 bytes
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// commit to-local revocation sig: 64 bytes
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// commit to-remote pubkey: 33 bytes, maybe blank
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// commit to-remote sig: 64 bytes, maybe blank
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func (b *JusticeKit) encodeV0(w io.Writer) error {
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// Write 42-byte sweep address where client funds will be deposited.
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_, err := w.Write(b.SweepAddress[:])
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if err != nil {
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return err
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}
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// Write 33-byte revocation public key.
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_, err = w.Write(b.RevocationPubKey[:])
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if err != nil {
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return err
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}
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// Write 33-byte local delay public key.
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_, err = w.Write(b.LocalDelayPubKey[:])
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if err != nil {
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return err
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}
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// Write 4-byte CSV delay.
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err = binary.Write(w, byteOrder, b.CSVDelay)
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if err != nil {
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return err
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}
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// Write 64-byte revocation signature for commit to-local output.
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_, err = w.Write(b.CommitToLocalSig[:])
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if err != nil {
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return err
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}
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// Write 33-byte commit to-remote public key, which may be blank.
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_, err = w.Write(b.CommitToRemotePubKey[:])
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if err != nil {
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return err
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}
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// Write 64-byte commit to-remote signature, which may be blank.
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_, err = w.Write(b.CommitToRemoteSig[:])
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return err
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}
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// decodeV0 reconstructs a JusticeKit from the io.Reader, using version 0
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// encoding scheme. This will parse a constant size input stream of 273 bytes to
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// recover information for the commit to-local output, and possibly the commit
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// to-remote output.
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//
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// blob version 0 plaintext encoding:
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// sweep address: 42 bytes
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// revocation pubkey: 33 bytes
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// local delay pubkey: 33 bytes
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// csv delay: 4 bytes
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// commit to-local revocation sig: 64 bytes
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// commit to-remote pubkey: 33 bytes, maybe blank
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// commit to-remote sig: 64 bytes, maybe blank
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func (b *JusticeKit) decodeV0(r io.Reader) error {
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// Read 42-byte sweep address where client funds will be deposited.
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_, err := io.ReadFull(r, b.SweepAddress[:])
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if err != nil {
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return err
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}
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// Read 33-byte revocation public key.
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_, err = io.ReadFull(r, b.RevocationPubKey[:])
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if err != nil {
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return err
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}
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// Read 33-byte local delay public key.
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_, err = io.ReadFull(r, b.LocalDelayPubKey[:])
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if err != nil {
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return err
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}
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// Read 4-byte CSV delay.
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err = binary.Read(r, byteOrder, &b.CSVDelay)
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if err != nil {
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return err
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}
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// Read 64-byte revocation signature for commit to-local output.
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_, err = io.ReadFull(r, b.CommitToLocalSig[:])
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if err != nil {
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return err
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}
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var (
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commitToRemotePubkey PubKey
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commitToRemoteSig lnwire.Sig
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)
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// Read 33-byte commit to-remote public key, which may be discarded.
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_, err = io.ReadFull(r, commitToRemotePubkey[:])
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if err != nil {
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return err
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}
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// Read 64-byte commit to-remote signature, which may be discarded.
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_, err = io.ReadFull(r, commitToRemoteSig[:])
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if err != nil {
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return err
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}
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// Only populate the commit to-remote fields in the decoded blob if a
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// valid compressed public key was read from the reader.
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if btcec.IsCompressedPubKey(commitToRemotePubkey[:]) {
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b.CommitToRemotePubKey = commitToRemotePubkey
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b.CommitToRemoteSig = commitToRemoteSig
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}
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return nil
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}
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