Add two new functions: EncodePrivateKey and DecodePrivateKey

EncodePrivateKey encodes a raw private key into Wallet Import Format.
DecodePrivateKey decodes the WIF string to a raw private key.

addrconvs.go

@@ -95,3 +95,46 @@ func DecodeAddress(addr string) (addrHash []byte, net btcwire.BitcoinNet, err er
 
 	return addrHash, net, nil
 }
+
+// EncodePrivateKey takes a 32-byte raw private key address and encodes
+// it into the Wallet Import Format (WIF)
+func EncodePrivateKey(privKey []byte) (string, error) {
+	if len(privKey) != 32 {
+		return "", ErrMalformedAddress
+	}
+
+	tosum := append([]byte{0x80}, privKey...)
+	cksum := btcwire.DoubleSha256(tosum)
+
+	// Address before base58 encoding is 1 byte for 0x80 (5), 32 bytes for
+	// privKey, plus 4 bytes of checksum.
+	a := make([]byte, 37, 37)
+	a[0] = 0x80
+	copy(a[1:], privKey)
+	copy(a[32+1:], cksum[:4])
+
+	return Base58Encode(a), nil
+}
+
+// DecodePrivateKey takes a Wallet Import Format (WIF) string and
+// decodes into a 32-byte private key.
+func DecodePrivateKey(wif string) ([]byte, error) {
+	decoded := Base58Decode(wif)
+
+	// Length of decoded privkey must be 32 bytes + 1 byte for 0x80
+	// + 4 bytes of checksum
+	if len(decoded) != 32+5 {
+		return nil, ErrMalformedAddress
+	}
+
+	tosum := decoded[:32+1]
+	cksum := btcwire.DoubleSha256(tosum)[:4]
+	if !bytes.Equal(cksum, decoded[len(decoded)-4:]) {
+		return nil, ErrMalformedAddress
+	}
+
+	privKey := make([]byte, 32, 32)
+	copy(privKey[:], decoded[1:32+1])
+
+	return privKey, nil
+}

addrconvs_test.go

@@ -11,6 +11,18 @@ import (
 	"testing"
 )
 
+var encodePrivateKeyTests = []struct {
+	in  []byte
+	out string
+}{
+	{[]byte{
+		0x0c, 0x28, 0xfc, 0xa3, 0x86, 0xc7, 0xa2, 0x27,
+		0x60, 0x0b, 0x2f, 0xe5, 0x0b, 0x7c, 0xae, 0x11,
+		0xec, 0x86, 0xd3, 0xbf, 0x1f, 0xbe, 0x47, 0x1b,
+		0xe8, 0x98, 0x27, 0xe1, 0x9d, 0x72, 0xaa, 0x1d,
+	}, "5HueCGU8rMjxEXxiPuD5BDku4MkFqeZyd4dZ1jvhTVqvbTLvyTJ"},
+}
+
 var encodeTests = []struct {
 	raw []byte
 	net btcwire.BitcoinNet
@@ -91,3 +103,29 @@ func TestDecodeAddresses(t *testing.T) {
 		}
 	}
 }
+
+func TestEncodeDecodePrivateKey(t *testing.T) {
+	for _, test := range encodePrivateKeyTests {
+		wif, err := btcutil.EncodePrivateKey(test.in)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if wif != test.out {
+			t.Errorf("TestEncodeDecodePrivateKey failed: want '%s', got '%s'",
+				test.out, wif)
+			continue
+		}
+
+		key, err := btcutil.DecodePrivateKey(test.out)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if !bytes.Equal(key, test.in) {
+			t.Errorf("TestEncodeDecodePrivateKey failed: want '%x', got '%x'",
+				test.out, key)
+		}
+
+	}
+}