130 lines
4.1 KiB
Go
130 lines
4.1 KiB
Go
package lnwire
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import (
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"fmt"
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"github.com/btcsuite/btcd/btcec"
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"github.com/lightningnetwork/lnd/input"
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)
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// Sig is a fixed-sized ECDSA signature. Unlike Bitcoin, we use fixed sized
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// signatures on the wire, instead of DER encoded signatures. This type
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// provides several methods to convert to/from a regular Bitcoin DER encoded
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// signature (raw bytes and *btcec.Signature).
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type Sig [64]byte
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// NewSigFromRawSignature returns a Sig from a Bitcoin raw signature encoded in
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// the canonical DER encoding.
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func NewSigFromRawSignature(sig []byte) (Sig, error) {
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var b Sig
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if len(sig) == 0 {
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return b, fmt.Errorf("cannot decode empty signature")
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}
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// Extract lengths of R and S. The DER representation is laid out as
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// 0x30 <length> 0x02 <length r> r 0x02 <length s> s
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// which means the length of R is the 4th byte and the length of S
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// is the second byte after R ends. 0x02 signifies a length-prefixed,
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// zero-padded, big-endian bigint. 0x30 signifies a DER signature.
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// See the Serialize() method for btcec.Signature for details.
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rLen := sig[3]
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sLen := sig[5+rLen]
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// Check to make sure R and S can both fit into their intended buffers.
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// We check S first because these code blocks decrement sLen and rLen
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// in the case of a 33-byte 0-padded integer returned from Serialize()
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// and rLen is used in calculating array indices for S. We can track
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// this with additional variables, but it's more efficient to just
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// check S first.
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if sLen > 32 {
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if (sLen > 33) || (sig[6+rLen] != 0x00) {
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return b, fmt.Errorf("S is over 32 bytes long " +
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"without padding")
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}
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sLen--
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copy(b[64-sLen:], sig[7+rLen:])
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} else {
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copy(b[64-sLen:], sig[6+rLen:])
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}
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// Do the same for R as we did for S
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if rLen > 32 {
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if (rLen > 33) || (sig[4] != 0x00) {
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return b, fmt.Errorf("R is over 32 bytes long " +
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"without padding")
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}
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rLen--
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copy(b[32-rLen:], sig[5:5+rLen])
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} else {
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copy(b[32-rLen:], sig[4:4+rLen])
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}
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return b, nil
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}
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// NewSigFromSignature creates a new signature as used on the wire, from an
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// existing btcec.Signature.
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func NewSigFromSignature(e input.Signature) (Sig, error) {
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if e == nil {
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return Sig{}, fmt.Errorf("cannot decode empty signature")
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}
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// Serialize the signature with all the checks that entails.
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return NewSigFromRawSignature(e.Serialize())
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}
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// ToSignature converts the fixed-sized signature to a btcec.Signature objects
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// which can be used for signature validation checks.
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func (b *Sig) ToSignature() (*btcec.Signature, error) {
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// Parse the signature with strict checks.
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sigBytes := b.ToSignatureBytes()
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sig, err := btcec.ParseDERSignature(sigBytes, btcec.S256())
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if err != nil {
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return nil, err
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}
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return sig, nil
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}
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// ToSignatureBytes serializes the target fixed-sized signature into the raw
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// bytes of a DER encoding.
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func (b *Sig) ToSignatureBytes() []byte {
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// Extract canonically-padded bigint representations from buffer
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r := extractCanonicalPadding(b[0:32])
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s := extractCanonicalPadding(b[32:64])
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rLen := uint8(len(r))
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sLen := uint8(len(s))
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// Create a canonical serialized signature. DER format is:
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// 0x30 <length> 0x02 <length r> r 0x02 <length s> s
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sigBytes := make([]byte, 6+rLen+sLen)
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sigBytes[0] = 0x30 // DER signature magic value
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sigBytes[1] = 4 + rLen + sLen // Length of rest of signature
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sigBytes[2] = 0x02 // Big integer magic value
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sigBytes[3] = rLen // Length of R
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sigBytes[rLen+4] = 0x02 // Big integer magic value
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sigBytes[rLen+5] = sLen // Length of S
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copy(sigBytes[4:], r) // Copy R
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copy(sigBytes[rLen+6:], s) // Copy S
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return sigBytes
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}
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// extractCanonicalPadding is a utility function to extract the canonical
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// padding of a big-endian integer from the wire encoding (a 0-padded
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// big-endian integer) such that it passes btcec.canonicalPadding test.
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func extractCanonicalPadding(b []byte) []byte {
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for i := 0; i < len(b); i++ {
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// Found first non-zero byte.
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if b[i] > 0 {
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// If the MSB is set, we need zero padding.
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if b[i]&0x80 == 0x80 {
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return append([]byte{0x00}, b[i:]...)
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}
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return b[i:]
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}
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}
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return []byte{0x00}
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}
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