"config": {
        "chainId": 555,
        "homesteadBlock": 0,
        "eip155Block": 0,//homestead和eip155两种版本都不是，那么就是Frontier版本了，所以v的值为27或28，看下面代码解释
        "eip158Block": 0
    },

0: Olympic, Ethereum public pre-release testnet
1: Frontier, Homestead, Metropolis, the Ethereum public main network
1: Classic, the (un)forked public Ethereum Classic main network, chain ID 61
1: Expanse, an alternative Ethereum implementation, chain ID 2
2: Morden, the public Ethereum testnet, now Ethereum Classic testnet
3: Ropsten, the public cross-client Ethereum testnet
4: Rinkeby, the public Geth PoA testnet
8: Ubiq, the public Gubiq main network with flux difficulty chain ID 8
42: Kovan, the public Parity PoA testnet
77: Sokol, the public POA Network testnet
99: Core, the public POA Network main network
7762959: Musicoin, the music blockchain
61717561: Aquachain, ASIC resistant chain
[Other]: Could indicate that your connected to a local development test network.

// EIP155Transaction implements Signer using the EIP155 rules.
type EIP155Signer struct {
    chainId, chainIdMul *big.Int
}

func NewEIP155Signer(chainId *big.Int) EIP155Signer {
    if chainId == nil {
        chainId = new(big.Int)
    }
    return EIP155Signer{
        chainId:    chainId,
        chainIdMul: new(big.Int).Mul(chainId, big.NewInt(2)),
    }
}

func (s EIP155Signer) Equal(s2 Signer) bool {
    eip155, ok := s2.(EIP155Signer)
    return ok && eip155.chainId.Cmp(s.chainId) == 0
}

var big8 = big.NewInt(8)

func (s EIP155Signer) Sender(tx *Transaction) (common.Address, error) {
    if !tx.Protected() {
        return HomesteadSigner{}.Sender(tx)
    }
    if tx.ChainId().Cmp(s.chainId) != 0 {
        return common.Address{}, ErrInvalidChainId
    }
    V := new(big.Int).Sub(tx.data.V, s.chainIdMul)
    V.Sub(V, big8)
    return recoverPlain(s.Hash(tx), tx.data.R, tx.data.S, V, true)
}

// WithSignature returns a new transaction with the given signature. This signature
// needs to be in the [R || S || V] format where V is 0 or 1.
func (s EIP155Signer) SignatureValues(tx *Transaction, sig []byte) (R, S, V *big.Int, err error) {
    R, S, V, err = HomesteadSigner{}.SignatureValues(tx, sig)
    if err != nil {
        return nil, nil, nil, err
    }
    if s.chainId.Sign() != 0 {
        V = big.NewInt(int64(sig[64] + 35))
        V.Add(V, s.chainIdMul)
    }
    return R, S, V, nil
}

// Hash returns the hash to be signed by the sender.
// It does not uniquely identify the transaction.
func (s EIP155Signer) Hash(tx *Transaction) common.Hash {
    return rlpHash([]interface{}{
        tx.data.AccountNonce,
        tx.data.Price,
        tx.data.GasLimit,
        tx.data.Recipient,
        tx.data.Amount,
        tx.data.Payload,
        s.chainId, uint(0), uint(0),
    })
}

// HomesteadTransaction implements TransactionInterface using the
// homestead rules.
type HomesteadSigner struct{ FrontierSigner }

func (s HomesteadSigner) Equal(s2 Signer) bool {
    _, ok := s2.(HomesteadSigner)
    return ok
}

// SignatureValues returns signature values. This signature
// needs to be in the [R || S || V] format where V is 0 or 1.
func (hs HomesteadSigner) SignatureValues(tx *Transaction, sig []byte) (r, s, v *big.Int, err error) {
    return hs.FrontierSigner.SignatureValues(tx, sig)
}

func (hs HomesteadSigner) Sender(tx *Transaction) (common.Address, error) {
    return recoverPlain(hs.Hash(tx), tx.data.R, tx.data.S, tx.data.V, true)
}

type FrontierSigner struct{}

func (s FrontierSigner) Equal(s2 Signer) bool {
    _, ok := s2.(FrontierSigner)
    return ok
}

// SignatureValues returns signature values. This signature
// needs to be in the [R || S || V] format where V is 0 or 1.
func (fs FrontierSigner) SignatureValues(tx *Transaction, sig []byte) (r, s, v *big.Int, err error) {
    if len(sig) != 65 {
        panic(fmt.Sprintf("wrong size for signature: got %d, want 65", len(sig)))
    }
    r = new(big.Int).SetBytes(sig[:32])
    s = new(big.Int).SetBytes(sig[32:64])
    v = new(big.Int).SetBytes([]byte{sig[64] + 27})
    return r, s, v, nil
}

// Hash returns the hash to be signed by the sender.
// It does not uniquely identify the transaction.
func (fs FrontierSigner) Hash(tx *Transaction) common.Hash {
    return rlpHash([]interface{}{
        tx.data.AccountNonce,
        tx.data.Price,
        tx.data.GasLimit,
        tx.data.Recipient,
        tx.data.Amount,
        tx.data.Payload,
    })
}

func (fs FrontierSigner) Sender(tx *Transaction) (common.Address, error) {
    return recoverPlain(fs.Hash(tx), tx.data.R, tx.data.S, tx.data.V, false)
}

func recoverPlain(sighash common.Hash, R, S, Vb *big.Int, homestead bool) (common.Address, error) {
    if Vb.BitLen() > 8 {
        return common.Address{}, ErrInvalidSig
    }
    V := byte(Vb.Uint64() - 27)
    if !crypto.ValidateSignatureValues(V, R, S, homestead) {
        return common.Address{}, ErrInvalidSig
    }
    // encode the snature in uncompressed format
    r, s := R.Bytes(), S.Bytes()
    sig := make([]byte, 65)
    copy(sig[32-len(r):32], r)
    copy(sig[64-len(s):64], s)
    sig[64] = V
    // recover the public key from the snature
    pub, err := crypto.Ecrecover(sighash[:], sig)
    if err != nil {
        return common.Address{}, err
    }
    if len(pub) == 0 || pub[0] != 4 {
        return common.Address{}, errors.New("invalid public key")
    }
    var addr common.Address
    copy(addr[:], crypto.Keccak256(pub[1:])[12:])
    return addr, nil
}

// Ecrecover returns the uncompressed public key that created the given signature.
func Ecrecover(hash, sig []byte) ([]byte, error) {
    return secp256k1.RecoverPubkey(hash, sig)
}

// RecoverPubkey returns the public key of the signer.
// msg must be the 32-byte hash of the message to be signed.
// sig must be a 65-byte compact ECDSA signature containing the recovery id as the last element.
func RecoverPubkey(msg []byte, sig []byte) ([]byte, error) {
    if len(msg) != 32 {
        return nil, ErrInvalidMsgLen
    }
    if err := checkSignature(sig); err != nil {
        return nil, err
    }

    var (
        pubkey  = make([]byte, 65)
        sigdata = (*C.uchar)(unsafe.Pointer(&sig[0]))
        msgdata = (*C.uchar)(unsafe.Pointer(&msg[0]))
    )
    if C.secp256k1_ext_ecdsa_recover(context, (*C.uchar)(unsafe.Pointer(&pubkey[0])), sigdata, msgdata) == 0 {
        return nil, ErrRecoverFailed
    }
    return pubkey, nil
}

int secp256k1_ecdsa_recover(const secp256k1_context* ctx, secp256k1_pubkey *pubkey, const secp256k1_ecdsa_recoverable_signature *signature, const unsigned char *msg32) {
    secp256k1_ge q;
    secp256k1_scalar r, s;
    secp256k1_scalar m;
    int recid;
    VERIFY_CHECK(ctx != NULL);
    ARG_CHECK(secp256k1_ecmult_context_is_built(&ctx->ecmult_ctx));
    ARG_CHECK(msg32 != NULL);
    ARG_CHECK(signature != NULL);
    ARG_CHECK(pubkey != NULL);

    secp256k1_ecdsa_recoverable_signature_load(ctx, &r, &s, &recid, signature);
    VERIFY_CHECK(recid >= 0 && recid < 4);  /* should have been caught in parse_compact */说明v可以为0，1，2，3
    secp256k1_scalar_set_b32(&m, msg32, NULL);
    if (secp256k1_ecdsa_sig_recover(&ctx->ecmult_ctx, &r, &s, &q, &m, recid)) {
        secp256k1_pubkey_save(pubkey, &q);
        return 1;
    } else {
        memset(pubkey, 0, sizeof(*pubkey));
        return 0;
    }
}

/** Group order for secp256k1 defined as 'n' in "Standards for Efficient Cryptography" (SEC2) 2.7.1
 *  sage: for t in xrange(1023, -1, -1):
 *     ..   p = 2**256 - 2**32 - t
 *     ..   if p.is_prime():
 *     ..     print '%x'%p
 *     ..     break
 *   'fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f'
 *  sage: a = 0
 *  sage: b = 7
 *  sage: F = FiniteField (p)
 *  sage: '%x' % (EllipticCurve ([F (a), F (b)]).order())
 *   'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141'
 */
static const secp256k1_fe_t secp256k1_ecdsa_const_order_as_fe = SECP256K1_FE_CONST(//这是私钥的最大值
    0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL,
    0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364141UL
);

/** Difference between field and order, values 'p' and 'n' values defined in
 *  "Standards for Efficient Cryptography" (SEC2) 2.7.1.
 *  sage: p = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F
 *  sage: a = 0
 *  sage: b = 7
 *  sage: F = FiniteField (p)
 *  sage: '%x' % (p - EllipticCurve ([F (a), F (b)]).order())
 *   '14551231950b75fc4402da1722fc9baee'
 */
static const secp256k1_fe_t secp256k1_ecdsa_const_p_minus_order = SECP256K1_FE_CONST(
    0, 0, 0, 1, 0x45512319UL, 0x50B75FC4UL, 0x402DA172UL, 0x2FC9BAEEUL
);

static int secp256k1_ecdsa_sig_recover(const secp256k1_ecmult_context *ctx, const secp256k1_scalar *sigr, const secp256k1_scalar* sigs, secp256k1_ge *pubkey, const secp256k1_scalar *message, int recid) {
    unsigned char brx[32];
    secp256k1_fe fx;
    secp256k1_ge x;
    secp256k1_gej xj;
    secp256k1_scalar rn, u1, u2;
    secp256k1_gej qj;
    int r;

    if (secp256k1_scalar_is_zero(sigr) || secp256k1_scalar_is_zero(sigs)) {
        return 0;
    }

    secp256k1_scalar_get_b32(brx, sigr);
    r = secp256k1_fe_set_b32(&fx, brx);
    (void)r;
    VERIFY_CHECK(r); /* brx comes from a scalar, so is less than the order; certainly less than p */
    if (recid & 2) {//用于获得v二进制倒数第二位的值，即当v = 2或3时，即二进制倒数第二位为1，才进入该判断语句
        if (secp256k1_fe_cmp_var(&fx, &secp256k1_ecdsa_const_p_minus_order) >= 0) {
　　　　　　　/* fx + p >= n, so we can skip testing the second case. */
            return 0;
        }
        secp256k1_fe_add(&fx, &secp256k1_ecdsa_const_order_as_fe);
    }
    //所以走到这的即v = 0或1的签名
    if (!secp256k1_ge_set_xo_var(&x, &fx, recid & 1)) {
        return 0;
    }
    //前面这部分的内容真的很复杂，但是看起来像是进行一些检验
    secp256k1_gej_set_ge(&xj, &x);
    secp256k1_scalar_inverse_var(&rn, sigr);
    secp256k1_scalar_mul(&u1, &rn, message);
    secp256k1_scalar_negate(&u1, &u1);
    secp256k1_scalar_mul(&u2, &rn, sigs);
    secp256k1_ecmult(ctx, &qj, &xj, &u2, &u1);
    secp256k1_ge_set_gej_var(pubkey, &qj);
    return !secp256k1_gej_is_infinity(&qj);
}

static int secp256k1_fe_cmp_var(const secp256k1_fe *a, const secp256k1_fe *b) {
    int i;
#ifdef VERIFY
    VERIFY_CHECK(a->normalized);
    VERIFY_CHECK(b->normalized);
    secp256k1_fe_verify(a);
    secp256k1_fe_verify(b);
#endif
    for (i = 4; i >= 0; i--) {
        if (a->n[i] > b->n[i]) {
            return 1;
        }
        if (a->n[i] < b->n[i]) {
            return -1;
        }
    }
    return 0;
}

#ifdef VERIFY
static void secp256k1_fe_verify(const secp256k1_fe *a) {
    const uint64_t *d = a->n;
    int m = a->normalized ? 1 : 2 * a->magnitude, r = 1;
   /* secp256k1 'p' value defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1. */
    r &= (d[0] <= 0xFFFFFFFFFFFFFULL * m);
    r &= (d[1] <= 0xFFFFFFFFFFFFFULL * m);
    r &= (d[2] <= 0xFFFFFFFFFFFFFULL * m);
    r &= (d[3] <= 0xFFFFFFFFFFFFFULL * m);
    r &= (d[4] <= 0x0FFFFFFFFFFFFULL * m);
    r &= (a->magnitude >= 0);
    r &= (a->magnitude <= 2048);
    if (a->normalized) {
        r &= (a->magnitude <= 1);
        if (r && (d[4] == 0x0FFFFFFFFFFFFULL) && ((d[3] & d[2] & d[1]) == 0xFFFFFFFFFFFFFULL)) {
            r &= (d[0] < 0xFFFFEFFFFFC2FULL);
        }
    }
    VERIFY_CHECK(r == 1);
}
#endif

SECP256K1_INLINE static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_fe *a) {
#ifdef VERIFY
    secp256k1_fe_verify(a);
#endif
    r->n[0] += a->n[0];
    r->n[1] += a->n[1];
    r->n[2] += a->n[2];
    r->n[3] += a->n[3];
    r->n[4] += a->n[4];
#ifdef VERIFY
    r->magnitude += a->magnitude;
    r->normalized = 0;
    secp256k1_fe_verify(r);
#endif
}

static int secp256k1_ge_set_xo_var(secp256k1_ge *r, const secp256k1_fe *x, int odd) {
    if (!secp256k1_ge_set_xquad(r, x)) {
        return 0;
    }
    secp256k1_fe_normalize_var(&r->y);
    if (secp256k1_fe_is_odd(&r->y) != odd) {
        secp256k1_fe_negate(&r->y, &r->y, 1);
    }
    return 1;

}