Add functions to serialize an ecdsa public key.

internal_test.go

@@ -0,0 +1,11 @@
+// Copyright (c) 2013 Conformal Systems LLC.
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package btcec
+
+const (
+	TstPubkeyUncompressed = pubkeyUncompressed
+	TstPubkeyCompressed   = pubkeyCompressed
+	TstPubkeyHybrid       = pubkeyHybrid
+)

pubkey.go

@@ -16,8 +16,8 @@ func isOdd(a *big.Int) bool {
 
 const (
 	pubkeyCompressed   byte = 0x2 // y_bit + x coord
-	pubkeyUncompressed      = 0x4 // x coord + y coord
-	pubkeyHybrid            = 0x6 // y_bit + x coord + y coord
+	pubkeyUncompressed byte = 0x4 // x coord + y coord
+	pubkeyHybrid       byte = 0x6 // y_bit + x coord + y coord
 )
 
 // ParsePubKey parses a public key for a koblitz curve from a bytestring into a
@@ -88,3 +88,42 @@ func ParsePubKey(pubKeyStr []byte, curve *KoblitzCurve) (key *ecdsa.PublicKey, e
 	}
 	return &pubkey, nil
 }
+
+// PublicKey is an ecdsa.PublicKey with additional functions to
+// serialize in uncompressed, compressed, and hybrid formats.
+type PublicKey ecdsa.PublicKey
+
+// SerializeUncompressed serializes a public key in a 65-byte uncompressed
+// format.
+func (p *PublicKey) SerializeUncompressed() []byte {
+	b := make([]byte, 65)
+	b[0] = pubkeyUncompressed
+	copy(b[1:33], p.X.Bytes())
+	copy(b[33:], p.Y.Bytes())
+	return b
+}
+
+// SerializeCompressed serializes a public key in a 33-byte compressed format.
+func (p *PublicKey) SerializeCompressed() []byte {
+	b := make([]byte, 33)
+	format := pubkeyCompressed
+	if isOdd(p.Y) {
+		format |= 0x1
+	}
+	b[0] = format
+	copy(b[1:33], p.X.Bytes())
+	return b
+}
+
+// SerializeHybrid serializes a public key in a 65-byte hybrid format.
+func (p *PublicKey) SerializeHybrid() []byte {
+	b := make([]byte, 65)
+	format := pubkeyHybrid
+	if isOdd(p.Y) {
+		format |= 0x1
+	}
+	b[0] = format
+	copy(b[1:33], p.X.Bytes())
+	copy(b[33:], p.Y.Bytes())
+	return b
+}

pubkey_test.go

@@ -5,13 +5,16 @@
 package btcec_test
 
 import (
+	"bytes"
 	"github.com/conformal/btcec"
+	"github.com/davecgh/go-spew/spew"
 	"testing"
 )
 
 type pubKeyTest struct {
 	name    string
 	key     []byte
+	format  byte
 	isValid bool
 }
 
@@ -30,6 +33,7 @@ var pubKeyTests = []pubKeyTest{
 			0xb4, 0x12, 0xa3,
 		},
 		isValid: true,
+		format:  btcec.TstPubkeyUncompressed,
 	},
 	pubKeyTest{
 		name: "uncompressed x changed",
@@ -82,6 +86,7 @@ var pubKeyTests = []pubKeyTest{
 			0xb4, 0x12, 0xa3,
 		},
 		isValid: true,
+		format:  btcec.TstPubkeyHybrid,
 	},
 	pubKeyTest{
 		name: "uncompressed as hybrid wrong",
@@ -105,6 +110,7 @@ var pubKeyTests = []pubKeyTest{
 			0xa9, 0xa1, 0xf4, 0x80, 0x9d, 0x3b, 0x4d,
 		},
 		isValid: true,
+		format:  btcec.TstPubkeyCompressed,
 	},
 	// from tx fdeb8e72524e8dab0da507ddbaf5f88fe4a933eb10a66bc4745bb0aa11ea393c
 	pubKeyTest{
@@ -115,6 +121,7 @@ var pubKeyTests = []pubKeyTest{
 			0x7f, 0x5b, 0x2a, 0x4b, 0x7d, 0x44, 0x8e,
 		},
 		isValid: true,
+		format:  btcec.TstPubkeyCompressed,
 	},
 	pubKeyTest{
 		name: "compressed claims uncompressed (ybit = 0)",
@@ -195,7 +202,7 @@ var pubKeyTests = []pubKeyTest{
 
 func TestPubKeys(t *testing.T) {
 	for _, test := range pubKeyTests {
-		_, err := btcec.ParsePubKey(test.key, btcec.S256())
+		pk, err := btcec.ParsePubKey(test.key, btcec.S256())
 		if err != nil {
 			if test.isValid {
 				t.Errorf("%s pubkey failed when shouldn't %v",
@@ -206,6 +213,22 @@ func TestPubKeys(t *testing.T) {
 		if !test.isValid {
 			t.Errorf("%s counted as valid when it should fail",
 				test.name)
+			continue
+		}
+		var pkStr []byte
+		switch test.format {
+		case btcec.TstPubkeyUncompressed:
+			pkStr = (*btcec.PublicKey)(pk).SerializeUncompressed()
+		case btcec.TstPubkeyCompressed:
+			pkStr = (*btcec.PublicKey)(pk).SerializeCompressed()
+		case btcec.TstPubkeyHybrid:
+			pkStr = (*btcec.PublicKey)(pk).SerializeHybrid()
+		}
+		if !bytes.Equal(test.key, pkStr) {
+			t.Errorf("%s pubkey: serialized keys do not match.",
+				test.name)
+			spew.Dump(test.key)
+			spew.Dump(pkStr)
 		}
 	}
 }

test_coverage.txt

@@ -2,19 +2,22 @@
 github.com/conformal/btcec/signature.go	 ParseSignature			 100.00% (41/41)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.doubleJacobian	 100.00% (21/21)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.ScalarMult	 100.00% (9/9)
-github.com/conformal/btcec/btcec.go	 initS256			 100.00% (7/7)
+github.com/conformal/btcec/pubkey.go	 PublicKey.SerializeHybrid	 100.00% (8/8)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.IsOnCurve		 100.00% (7/7)
+github.com/conformal/btcec/pubkey.go	 PublicKey.SerializeCompressed	 100.00% (7/7)
+github.com/conformal/btcec/btcec.go	 initS256			 100.00% (7/7)
+github.com/conformal/btcec/pubkey.go	 PublicKey.SerializeUncompressed 100.00% (5/5)
 github.com/conformal/btcec/btcec.go	 zForAffine			 100.00% (4/4)
-github.com/conformal/btcec/btcec.go	 KoblitzCurve.Add		 100.00% (3/3)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.QPlus1Div4	 100.00% (3/3)
+github.com/conformal/btcec/btcec.go	 KoblitzCurve.Add		 100.00% (3/3)
 github.com/conformal/btcec/btcec.go	 S256				 100.00% (2/2)
-github.com/conformal/btcec/btcec.go	 KoblitzCurve.Params		 100.00% (1/1)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.ScalarBaseMult	 100.00% (1/1)
-github.com/conformal/btcec/btcec.go	 initAll			 100.00% (1/1)
 github.com/conformal/btcec/pubkey.go	 isOdd				 100.00% (1/1)
+github.com/conformal/btcec/btcec.go	 initAll			 100.00% (1/1)
+github.com/conformal/btcec/btcec.go	 KoblitzCurve.Params		 100.00% (1/1)
 github.com/conformal/btcec/pubkey.go	 ParsePubKey			 96.88% (31/32)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.addJacobian	 91.67% (55/60)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.affineFromJacobian 90.00% (9/10)
 github.com/conformal/btcec/btcec.go	 KoblitzCurve.Double		 0.00% (0/2)
-github.com/conformal/btcec		 ------------------------------- 95.61% (196/205)
+github.com/conformal/btcec		 ------------------------------- 96.00% (216/225)