short.go

package ecc

import (
    "bytes"
    "crypto/ecdsa"
    "crypto/elliptic"
    "encoding/base64"
    "math/big"
    "regexp"
)

var crc8table = [256]byte{
    0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15,
    0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d,
    0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65,
    0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d,
    0xe0, 0xe7, 0xee, 0xe9, 0xfc, 0xfb, 0xf2, 0xf5,
    0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd,
    0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85,
    0xa8, 0xaf, 0xa6, 0xa1, 0xb4, 0xb3, 0xba, 0xbd,
    0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2,
    0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea,
    0xb7, 0xb0, 0xb9, 0xbe, 0xab, 0xac, 0xa5, 0xa2,
    0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a,
    0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32,
    0x1f, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0d, 0x0a,
    0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42,
    0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a,
    0x89, 0x8e, 0x87, 0x80, 0x95, 0x92, 0x9b, 0x9c,
    0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4,
    0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec,
    0xc1, 0xc6, 0xcf, 0xc8, 0xdd, 0xda, 0xd3, 0xd4,
    0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c,
    0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44,
    0x19, 0x1e, 0x17, 0x10, 0x05, 0x02, 0x0b, 0x0c,
    0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34,
    0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b,
    0x76, 0x71, 0x78, 0x7f, 0x6a, 0x6d, 0x64, 0x63,
    0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b,
    0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13,
    0xae, 0xa9, 0xa0, 0xa7, 0xb2, 0xb5, 0xbc, 0xbb,
    0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83,
    0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb,
    0xe6, 0xe1, 0xe8, 0xef, 0xfa, 0xfd, 0xf4, 0xf3,
}

func crc8(data []byte) byte {
    var crc byte
    for _, d := range data {
	crc = crc8table[d ^ crc]
    }
    return crc
}

func MarshalShortPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) {
    var buf bytes.Buffer
    curve := IdentifyCurve(key.Curve)
    if curve == nil {
	return nil, ErrUnsupportedCurve
    }
    b64 := base64.NewEncoder(base64.RawURLEncoding, &buf)
    b64.Write([]byte{0x79, 0xc7, curve.Id | 0x20, crc8(key.D.Bytes())})
    b64.Write(key.D.Bytes())
    b64.Close()
    return buf.Bytes(), nil
}

func MarshalShortPublicKey(key *ecdsa.PublicKey) ([]byte, error) {
    var buf bytes.Buffer
    curve := IdentifyCurve(key.Curve)
    if curve == nil {
	return nil, ErrUnsupportedCurve
    }
    b64 := base64.NewEncoder(base64.RawURLEncoding, &buf)
    data := elliptic.MarshalCompressed(key.Curve, key.X, key.Y)
    b64.Write([]byte{0x79, 0xc7, curve.Id, crc8(data)})
    b64.Write(data)
    b64.Close()
    return buf.Bytes(), nil
}

func MarshalShortKey(key interface{}) ([]byte, error) {
    if priv, ok := key.(*ecdsa.PrivateKey); ok {
	return MarshalShortPrivateKey(priv)
    }
    if pub, ok := key.(*ecdsa.PublicKey); ok {
	return MarshalShortPublicKey(pub)
    }
    return nil, ErrInvalidKey
}

func UnmarshalShortKeys(s []byte) ([]interface{}, error) {
    var keys []interface{}
    for _, match := range regexp.MustCompile(`\becc[0-9A-Za-z_-]+`).FindAllStringSubmatch(string(s), -1) {
	k := []byte(match[0])
	if len(k) < 8 {
	    return nil, ErrInvalidKey
	}
	buf := make([]byte, base64.RawURLEncoding.DecodedLen(len(k)))
	_, err := base64.RawURLEncoding.Decode(buf, k)
	if err != nil {
	    return nil, err
	}
	if len(buf) < 5 || buf[0] != 0x79 || buf[1] != 0xc7 {
	    return nil, ErrInvalidKey
	}
	var curve elliptic.Curve
	for _, c := range Curves {
	    if c.Id == (buf[2] & 0x1f) {
		curve = c.Curve()
	    }
	}
	if curve == nil {
	    return nil, ErrUnsupportedCurve
	}
	if buf[3] != crc8(buf[4:]) {
	    return nil, ErrInvalidKey
	}
	if buf[2] & 0x20 != 0 {
	    priv := new(ecdsa.PrivateKey)
	    priv.D = big.NewInt(0)
	    priv.D.SetBytes(buf[4:])
	    priv.PublicKey.Curve = curve
	    priv.PublicKey.X, priv.PublicKey.Y = curve.ScalarBaseMult(buf[4:])
	    keys = append(keys, priv)
	} else {
	    pub := new(ecdsa.PublicKey)
	    pub.Curve = curve
	    if buf[4] == 2 || buf[4] == 3 {
		pub.X, pub.Y = elliptic.UnmarshalCompressed(curve, buf[4:])
	    } else if buf[4] == 4 {
		pub.X, pub.Y = elliptic.Unmarshal(curve, buf[4:])
	    }
	    if pub.X == nil || pub.Y == nil {
		return nil, ErrInvalidKey
	    }
	    keys = append(keys, pub)
	}
    }
    return keys, nil
}

func UnmarshalShortPrivateKey(s []byte) (*ecdsa.PrivateKey, error) {
    keys, err := UnmarshalShortKeys(s)
    if err != nil {
	return nil, err
    }
    for _, key := range keys {
	if priv, ok := key.(*ecdsa.PrivateKey); ok {
	    return priv, nil
	}
    }
    return nil, ErrInvalidKey
}

func UnmarshalShortPublicKey(s []byte) (*ecdsa.PublicKey, error) {
    keys, err := UnmarshalShortKeys(s)
    if err != nil {
	return nil, err
    }
    for _, key := range keys {
	if pub, ok := key.(*ecdsa.PublicKey); ok {
	    return pub, nil
	}
    }
    for _, key := range keys {
	if priv, ok := key.(*ecdsa.PrivateKey); ok {
	    return &priv.PublicKey, nil
	}
    }
    return nil, ErrInvalidKey
}