// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package rsa implements RSA encryption as specified in PKCS #1 and RFC 8017.
//
// RSA is a single, fundamental operation that is used in this package to
// implement either public-key encryption or public-key signatures.
//
// The original specification for encryption and signatures with RSA is PKCS #1
// and the terms "RSA encryption" and "RSA signatures" by default refer to
// PKCS #1 version 1.5. However, that specification has flaws and new designs
// should use version 2, usually called by just OAEP and PSS, where
// possible.
//
// Two sets of interfaces are included in this package. When a more abstract
// interface isn't necessary, there are functions for encrypting/decrypting
// with v1.5/OAEP and signing/verifying with v1.5/PSS. If one needs to abstract
// over the public key primitive, the PrivateKey type implements the
// Decrypter and Signer interfaces from the crypto package.
//
// The RSA operations in this package are not implemented using constant-time algorithms.

package internal

import (
	"crypto"
	cryptoRSA "crypto/rsa"

	"crypto/subtle"
	"errors"
	"io"
	"math/big"

	"xdx.jelly/xgcl/api/common"
	"xdx.jelly/xgcl/gmath"
	"xdx.jelly/xgcl/internal/randutil"
	"xdx.jelly/xgcl/sm"
)

// A PublicKey represents the public part of an RSA key.
type PublicKey struct {
	N *big.Int // modulus
	E int      // public exponent
}

func NewPublicKey() *PublicKey {
	return &PublicKey{
		N: new(big.Int),
	}
}

type PrecomputedValues = cryptoRSA.PrecomputedValues

// type PrecomputedValues struct {
// 	Dp, Dq *big.Int // D mod (P-1) (or mod Q-1)
// 	Qinv   *big.Int // Q^-1 mod P

// 	// CRTValues is used for the 3rd and subsequent primes. Due to a
// 	// historical accident, the CRT for the first two primes is handled
// 	// differently in PKCS #1 and interoperability is sufficiently
// 	// important that we mirror this.
// 	CRTValues []CRTValue
// }

// CRTValue contains the precomputed Chinese remainder theorem values.
type CRTValue = cryptoRSA.CRTValue

// type CRTValue struct {
// 	Exp   *big.Int // D mod (prime-1).
// 	Coeff *big.Int // R·Coeff ≡ 1 mod Prime.
// 	R     *big.Int // product of primes prior to this (inc p and q).
// }

// A PrivateKey represents an RSA key
// type PrivateKey = rsa.PrivateKey
type PrivateKey struct {
	PublicKey            // public part.
	D         *big.Int   // private exponent
	Primes    []*big.Int // prime factors of N, has >= 2 elements.

	// Precomputed contains precomputed values that speed up private
	// operations, if available.
	Precomputed PrecomputedValues
}

func NewPrivateKey() *PrivateKey {
	return &PrivateKey{
		PublicKey: PublicKey{
			N: new(big.Int),
		},
		D:      new(big.Int),
		Primes: []*big.Int{new(big.Int), new(big.Int)},
	}

}

func (pub *PublicKey) From(k *cryptoRSA.PublicKey) {
	pub.N = k.N
	pub.E = k.E
}

func (pub *PublicKey) UnmarshalCryptoRsa(k *cryptoRSA.PublicKey) *PublicKey {
	pub.From(k)
	return pub
}

func (pub *PublicKey) Into() *cryptoRSA.PublicKey {
	return &cryptoRSA.PublicKey{
		N: pub.N,
		E: pub.E,
	}
}

func (pub *PublicKey) Equal(x crypto.PublicKey) bool {
	switch xx := x.(type) {
	case *PublicKey:
		return pub.N.Cmp(xx.N) == 0 && pub.E == xx.E
	case *cryptoRSA.PublicKey:
		return pub.N.Cmp(xx.N) == 0 && pub.E == xx.E
	default:
		return false
	}
}

func (priv *PrivateKey) From(k *cryptoRSA.PrivateKey) *PrivateKey {
	priv.PublicKey.From(&k.PublicKey)
	priv.D = k.D
	priv.Primes = k.Primes
	priv.Precomputed = k.Precomputed
	return priv
}

func (priv *PrivateKey) Into() *cryptoRSA.PrivateKey {
	return &cryptoRSA.PrivateKey{
		PublicKey: cryptoRSA.PublicKey{
			N: priv.PublicKey.N,
			E: priv.PublicKey.E,
		},
		D:           priv.D,
		Primes:      priv.Primes,
		Precomputed: priv.Precomputed,
	}
}

var (
	errPublicModulus       = errors.New("crypto/rsa: missing public modulus")
	errPublicExponentSmall = errors.New("crypto/rsa: public exponent too small")
	errPublicExponentLarge = errors.New("crypto/rsa: public exponent too large")
)

// checkPub sanity checks the public key before we use it.
// We require pub.E to fit into a 32-bit integer so that we
// do not have different behavior depending on whether
// int is 32 or 64 bits. See also
// https://www.imperialviolet.org/2012/03/16/rsae.html.
func checkPub(pub *PublicKey) error {
	if pub.N == nil {
		return errPublicModulus
	}
	if pub.E < 2 {
		return errPublicExponentSmall
	}
	if pub.E > 1<<31-1 {
		return errPublicExponentLarge
	}
	return nil
}

// Validate performs basic sanity checks on the key.
// It returns nil if the key is valid, or else an error describing a problem.
func (priv *PrivateKey) Validate() error {
	if err := checkPub(&priv.PublicKey); err != nil {
		return err
	}

	// Check that Πprimes == n.
	modulus := new(big.Int).Set(bigOne)
	for _, prime := range priv.Primes {
		// Any primes ≤ 1 will cause divide-by-zero panics later.
		if prime.Cmp(bigOne) <= 0 {
			return errors.New("crypto/rsa: invalid prime value")
		}
		modulus.Mul(modulus, prime)
	}
	if modulus.Cmp(priv.N) != 0 {
		return errors.New("crypto/rsa: invalid modulus")
	}

	// Check that de ≡ 1 mod p-1, for each prime.
	// This implies that e is coprime to each p-1 as e has a multiplicative
	// inverse. Therefore e is coprime to lcm(p-1,q-1,r-1,...) =
	// exponent(ℤ/nℤ). It also implies that a^de ≡ a mod p as a^(p-1) ≡ 1
	// mod p. Thus a^de ≡ a mod n for all a coprime to n, as required.
	congruence := new(big.Int)
	de := new(big.Int).SetInt64(int64(priv.E))
	de.Mul(de, priv.D)
	for _, prime := range priv.Primes {
		pminus1 := new(big.Int).Sub(prime, bigOne)
		congruence.Mod(de, pminus1)
		if congruence.Cmp(bigOne) != 0 {
			return errors.New("crypto/rsa: invalid exponents")
		}
	}
	return nil
}

// Precompute performs some calculations that speed up private key operations
// in the future.
func (priv *PrivateKey) Precompute() {
	if priv.Precomputed.Dp != nil {
		return
	}

	priv.Precomputed.Dp = new(big.Int).Sub(priv.Primes[0], bigOne)
	priv.Precomputed.Dp.Mod(priv.D, priv.Precomputed.Dp)

	priv.Precomputed.Dq = new(big.Int).Sub(priv.Primes[1], bigOne)
	priv.Precomputed.Dq.Mod(priv.D, priv.Precomputed.Dq)

	priv.Precomputed.Qinv = new(big.Int).ModInverse(priv.Primes[1], priv.Primes[0])

	r := new(big.Int).Mul(priv.Primes[0], priv.Primes[1])
	priv.Precomputed.CRTValues = make([]CRTValue, len(priv.Primes)-2)
	for i := 2; i < len(priv.Primes); i++ {
		prime := priv.Primes[i]
		values := &priv.Precomputed.CRTValues[i-2]

		values.Exp = new(big.Int).Sub(prime, bigOne)
		values.Exp.Mod(priv.D, values.Exp)

		values.R = new(big.Int).Set(r)
		values.Coeff = new(big.Int).ModInverse(r, prime)

		r.Mul(r, prime)
	}
}

// UnmarshalSDF import privateKey from SDF type.
func (priv *PrivateKey) UnmarshalSDF(sdfPriv *common.RSArefPrivateKey) error {
	return priv.FromSDF(sdfPriv)
}
func (priv *PrivateKey) FromSDF(sdfPriv *common.RSArefPrivateKey) error {
	if priv.PublicKey.N == nil {
		priv.PublicKey.N = new(big.Int)
	}
	priv.N.SetBytes(sdfPriv.M[:])

	if priv.D == nil {
		priv.D = new(big.Int)
	}
	priv.D.SetBytes(sdfPriv.D[:])

	// E always be 65537
	e := new(big.Int).SetBytes(sdfPriv.E[:])
	if e.BitLen() > 32 {
		return common.SDR_KEYERR
	}
	priv.E = int(e.Uint64())

	priv.Primes = append(priv.Primes[:0], new(big.Int).SetBytes(sdfPriv.Prime[0][:]))
	priv.Primes = append(priv.Primes, new(big.Int).SetBytes(sdfPriv.Prime[1][:]))
	priv.Precompute()
	return priv.Validate()
}

// Export export privateKey to SDF type.
func (priv *PrivateKey) IntoSDF() (*common.RSArefPrivateKey, error) {
	ret := &common.RSArefPrivateKey{}
	if err := priv.UnmarshalSDF(ret); err != nil {
		return nil, err
	}
	return ret, nil
}

func (priv *PrivateKey) MarshalSDF(sdfPriv *common.RSArefPrivateKey) error {
	if err := priv.Validate(); err != nil {
		return err
	}
	priv.Precompute()
	sdfPriv.Bits = uint32(priv.N.BitLen())
	if sdfPriv.Bits > common.RSAref_MAX_BITS || len(priv.Primes) != 2 {
		return common.SDR_KEYERR
	}
	_ = gmath.FillBytes(priv.N, sdfPriv.M[:])
	_ = gmath.FillBytes(new(big.Int).SetInt64(int64(priv.E)), sdfPriv.E[:]) // FIXME
	_ = gmath.FillBytes(priv.D, sdfPriv.D[:])
	_ = gmath.FillBytes(priv.Primes[0], sdfPriv.Prime[0][:])
	_ = gmath.FillBytes(priv.Primes[1], sdfPriv.Prime[1][:])
	_ = gmath.FillBytes(priv.Precomputed.Dp, sdfPriv.Pexp[0][:])
	_ = gmath.FillBytes(priv.Precomputed.Dq, sdfPriv.Pexp[1][:])
	_ = gmath.FillBytes(priv.Precomputed.Qinv, sdfPriv.Coef[:])
	return nil
}

// Set set pbulicKey directly by M and E, big-endian bytes.
func (pub *PublicKey) Set(M []byte, E []byte) error {
	if pub.N == nil {
		pub.N = new(big.Int)
	}
	pub.N.SetBytes(M[:])

	e := new(Int).SetBytes(E[:])
	if e.BitLen() > 32 {
		return common.SDR_KEYERR
	}
	pub.E = int(e.Uint64())
	return nil
}

func (pub *PublicKey) IntoSDF() (*common.RSArefPublicKey, error) {
	ret := &common.RSArefPublicKey{}
	if err := pub.MarshalSDF(ret); err != nil {
		return nil, err
	}
	return ret, nil
}

// MarshalSDF export publicKey to SDF type.
func (pub *PublicKey) MarshalSDF(sdfPub *common.RSArefPublicKey) error {
	if err := checkPub(pub); err != nil {
		return err
	}
	sdfPub.Bits = uint32(pub.N.BitLen())
	if sdfPub.Bits > common.RSAref_MAX_BITS {
		return common.SDR_KEYERR
	}
	_ = gmath.FillBytes(pub.N, sdfPub.M[:])
	_ = gmath.FillBytes(new(big.Int).SetInt64(int64(pub.E)), sdfPub.E[:]) // FIXME
	return nil
}

// UnmarshalSDF import publicKey from SDF type.
func (pub *PublicKey) UnmarshalSDF(sdfPub *common.RSArefPublicKey) error {
	return pub.FromSDF(sdfPub)
}
func (pub *PublicKey) FromSDF(sdfPub *common.RSArefPublicKey) error {
	if pub.N == nil {
		pub.N = new(big.Int)
	}
	pub.N.SetBytes(sdfPub.M[:])

	e := new(big.Int).SetBytes(sdfPub.E[:])
	if e.BitLen() > 32 {
		return common.SDR_KEYERR
	}
	pub.E = int(e.Uint64())
	return checkPub(pub)
}

// Size returns the modulus size in bytes. Raw signatures and ciphertexts
// for or by this public key will have the same size.
func (pub *PublicKey) Size() int {
	return (pub.N.BitLen() + 7) / 8
}

// GenerateKey generates an RSA keypair of the given bit size using the
// random source random (for example, crypto/rand.Reader).
func GenerateKey(random io.Reader, bits int) (*PrivateKey, error) {
	priv, err := cryptoRSA.GenerateKey(random, bits)
	if err != nil {
		return nil, err
	}
	privateKey := &PrivateKey{}
	privateKey.From(priv)
	return privateKey, nil
}

// ErrDecryption represents a failure to decrypt a message.
// It is deliberately vague to avoid adaptive attacks.
var ErrDecryption = errors.New("crypto/rsa: decryption error")

// ErrVerification represents a failure to verify a signature.
// It is deliberately vague to avoid adaptive attacks.
var ErrVerification = errors.New("crypto/rsa: verification error")

// ErrMessageTooLong is returned when attempting to encrypt a message which is
// too large for the size of the public key.
var ErrMessageTooLong = errors.New("crypto/rsa: message too long for RSA public key size")

// This file implements encryption and decryption using PKCS #1 v1.5 padding.

// PKCS1v15DecrypterOpts is for passing options to PKCS #1 v1.5 decryption using
// the crypto.Decrypter interface.
type PKCS1v15DecryptOptions = cryptoRSA.PKCS1v15DecryptOptions

// EncryptPKCS1v15 encrypts the given message with RSA and the padding
// scheme from PKCS #1 v1.5.  The message must be no longer than the
// length of the public modulus minus 11 bytes.
//
// The rand parameter is used as a source of entropy to ensure that
// encrypting the same message twice doesn't result in the same
// ciphertext.
//
// WARNING: use of this function to encrypt plaintexts other than
// session keys is dangerous. Use RSA OAEP in new protocols.
func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) ([]byte, error) {
	// return rsa.EncryptPKCS1v15(rand, pub.Into(), msg)
	randutil.MaybeReadByte(rand)

	if err := checkPub(pub); err != nil {
		return nil, err
	}
	k := pub.Size()
	if len(msg) > k-11 {
		return nil, ErrMessageTooLong
	}

	// EM = 0x00 || 0x02 || PS || 0x00 || M
	em := make([]byte, k)
	em[1] = 2
	ps, mm := em[2:len(em)-len(msg)-1], em[len(em)-len(msg):]
	err := nonZeroRandomBytes(ps, rand)
	if err != nil {
		return nil, err
	}
	em[len(em)-len(msg)-1] = 0
	copy(mm, msg)

	m := new(big.Int).SetBytes(em)
	c := encrypt(new(big.Int), pub, m)
	gmath.FillBytes(c, em)
	return em, nil
}

// DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS #1 v1.5.
// If rand != nil, it uses RSA blinding to avoid timing side-channel attacks.
//
// Note that whether this function returns an error or not discloses secret
// information. If an attacker can cause this function to run repeatedly and
// learn whether each instance returned an error then they can decrypt and
// forge signatures as if they had the private key. See
// DecryptPKCS1v15SessionKey for a way of solving this problem.
func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) ([]byte, error) {
	// return rsa.DecryptPKCS1v15(rand, priv.Into(), ciphertext)
	if err := checkPub(&priv.PublicKey); err != nil {
		return nil, err
	}
	valid, out, index, err := decryptPKCS1v15(rand, priv, ciphertext)
	if err != nil {
		return nil, err
	}
	if valid == 0 {
		return nil, ErrDecryption
	}
	return out[index:], nil
}

// decryptPKCS1v15 decrypts ciphertext using priv and blinds the operation if
// rand is not nil. It returns one or zero in valid that indicates whether the
// plaintext was correctly structured. In either case, the plaintext is
// returned in em so that it may be read independently of whether it was valid
// in order to maintain constant memory access patterns. If the plaintext was
// valid then index contains the index of the original message in em.
func decryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (valid int, em []byte, index int, err error) {
	k := priv.Size()
	if k < 11 {
		err = ErrDecryption
		return
	}

	c := new(big.Int).SetBytes(ciphertext)
	m, err := decrypt(rand, priv, c)
	if err != nil {
		return
	}

	em = m.FillBytes(make([]byte, k))
	firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0)
	secondByteIsTwo := subtle.ConstantTimeByteEq(em[1], 2)

	// The remainder of the plaintext must be a string of non-zero random
	// octets, followed by a 0, followed by the message.
	//   lookingForIndex: 1 iff we are still looking for the zero.
	//   index: the offset of the first zero byte.
	lookingForIndex := 1

	for i := 2; i < len(em); i++ {
		equals0 := subtle.ConstantTimeByteEq(em[i], 0)
		index = subtle.ConstantTimeSelect(lookingForIndex&equals0, i, index)
		lookingForIndex = subtle.ConstantTimeSelect(equals0, 0, lookingForIndex)
	}

	// The PS padding must be at least 8 bytes long, and it starts two
	// bytes into em.
	validPS := subtle.ConstantTimeLessOrEq(2+8, index)

	valid = firstByteIsZero & secondByteIsTwo & (^lookingForIndex & 1) & validPS
	index = subtle.ConstantTimeSelect(valid, index+1, 0)
	return valid, em, index, nil
}

// nonZeroRandomBytes fills the given slice with non-zero random octets.
func nonZeroRandomBytes(s []byte, rand io.Reader) (err error) {
	_, err = io.ReadFull(rand, s)
	if err != nil {
		return
	}

	for i := 0; i < len(s); i++ {
		for s[i] == 0 {
			_, err = io.ReadFull(rand, s[i:i+1])
			if err != nil {
				return
			}
			// In tests, the PRNG may return all zeros so we do
			// this to break the loop.
			s[i] ^= 0x42
		}
	}

	return
}

// These are ASN1 DER structures:
//   DigestInfo ::= SEQUENCE {
//     digestAlgorithm AlgorithmIdentifier,
//     digest OCTET STRING
//   }
// For performance, we don't use the generic ASN1 encoder. Rather, we
// precompute a prefix of the digest value that makes a valid ASN1 DER string
// with the correct contents.
var hashPrefixes = map[sm.Hash][]byte{
	{Hash: crypto.SHA1}:   {0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
	{Hash: crypto.SHA256}: {0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
	sm.SM3:                {0x30, 0x2e, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x81, 0x1c, 0xcf, 0x55, 0x01, 0x83, 0x11, 0x01, 0x05, 0x00, 0x04, 0x20},
}

func pkcs1v15HashInfo(hash sm.Hash, inLen int) (hashLen int, prefix []byte, err error) {
	// Special case: crypto.Hash(0) is used to indicate that the data is
	// signed directly.
	if hash.Hash == 0 {
		return inLen, nil, nil
	}

	hashLen = hash.Size()
	if inLen != hashLen {
		return 0, nil, errors.New("gcl/rsa: input must be hashed message")
	}
	prefix, ok := hashPrefixes[hash]
	if !ok {
		return 0, nil, errors.New("gcl/rsa: unsupported hash function")
	}
	return
}

// SignPKCS1v15 calculates the signature of hashed using
// RSASSA-PKCS1-V1_5-SIGN from RSA PKCS #1 v1.5.  Note that hashed must
// be the result of hashing the input message using the given hash
// function. If hash is zero, hashed is signed directly. This isn't
// advisable except for interoperability.
//
// If rand is not nil then RSA blinding will be used to avoid timing
// side-channel attacks.
//
// This function is deterministic. Thus, if the set of possible
// messages is small, an attacker may be able to build a map from
// messages to signatures and identify the signed messages. As ever,
// signatures provide authenticity, not confidentiality.
func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash sm.Hash, hashed []byte) ([]byte, error) {
	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
	if err != nil {
		return nil, err
	}

	tLen := len(prefix) + hashLen
	k := priv.Size()
	if k < tLen+11 {
		return nil, errors.New("rsa: message too long for RSA public key size")
	}

	// EM = 0x00 || 0x01 || PS || 0x00 || T
	em := make([]byte, k)
	em[1] = 1
	for i := 2; i < k-tLen-1; i++ {
		em[i] = 0xff
	}
	copy(em[k-tLen:k-hashLen], prefix)
	copy(em[k-hashLen:k], hashed)

	m := new(big.Int).SetBytes(em)
	c, err := decryptAndCheck(rand, priv, m)
	if err != nil {
		return nil, err
	}

	return c.FillBytes(em), nil

	// return rsa.SignPKCS1v15(rand, priv, hash.Hash, hashed)
}

// VerifyPKCS1v15 verifies an RSA PKCS #1 v1.5 signature.
// hashed is the result of hashing the input message using the given hash
// function and sig is the signature. A valid signature is indicated by
// returning a nil error. If hash is zero then hashed is used directly. This
// isn't advisable except for interoperability.
func VerifyPKCS1v15(pub *PublicKey, hash sm.Hash, hashed []byte, sig []byte) error {
	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
	if err != nil {
		return err
	}

	tLen := len(prefix) + hashLen
	k := pub.Size()
	if k < tLen+11 {
		return ErrVerification
	}

	// RFC 8017 Section 8.2.2: If the length of the signature S is not k
	// octets (where k is the length in octets of the RSA modulus n), output
	// "invalid signature" and stop.
	if k != len(sig) {
		return ErrVerification
	}

	c := new(big.Int).SetBytes(sig)
	m := encrypt(new(big.Int), pub, c)
	em := m.FillBytes(make([]byte, k))
	// EM = 0x00 || 0x01 || PS || 0x00 || T

	ok := subtle.ConstantTimeByteEq(em[0], 0)
	ok &= subtle.ConstantTimeByteEq(em[1], 1)
	ok &= subtle.ConstantTimeCompare(em[k-hashLen:k], hashed)
	ok &= subtle.ConstantTimeCompare(em[k-tLen:k-hashLen], prefix)
	ok &= subtle.ConstantTimeByteEq(em[k-tLen-1], 0)

	for i := 2; i < k-tLen-1; i++ {
		ok &= subtle.ConstantTimeByteEq(em[i], 0xff)
	}

	if ok != 1 {
		return ErrVerification
	}

	return nil

	// return rsa.VerifyPKCS1v15(pub, hash.Hash, hashed, sig)
}

func decryptAndCheck(random io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err error) {
	m, err = decrypt(random, priv, c)
	if err != nil {
		return nil, err
	}

	// In order to defend against errors in the CRT computation, m^e is
	// calculated, which should match the original ciphertext.
	check := encrypt(new(big.Int), &priv.PublicKey, m)
	if c.Cmp(check) != 0 {
		return nil, errors.New("rsa: internal error")
	}
	return m, nil
}

// PublicKeyOperationRSA RSA公钥运算。数据格式由应用层封装。inData 应该小于 privateKey.Size()
func PublicKeyOperationRSA(publicKey *PublicKey, inData []byte) ([]byte, error) {
	m := new(big.Int).SetBytes(inData)
	if m.Cmp(publicKey.N) >= 0 {
		return nil, common.SDR_INARGERR
	}
	c := encrypt(new(big.Int), publicKey, m)
	ret := make([]byte, common.RSAref_MAX_LEN)
	err := gmath.FillBytes(c, ret)
	return ret, err
}

// PrivateKeyOperationRSA RSA私钥运算。数据格式由应用层封装。inData 应该小于 privateKey.Bits/8
func PrivateKeyOperationRSA(privateKey *PrivateKey, inData []byte) ([]byte, error) {
	c := new(big.Int).SetBytes(inData)
	if c.Cmp(privateKey.N) >= 0 {
		return nil, common.SDR_INARGERR
	}
	m, err := decrypt(nil, privateKey, c)
	if err != nil {
		return nil, err
	}
	ret := make([]byte, common.RSAref_MAX_LEN)
	err = gmath.FillBytes(m, ret)
	return ret, err
}

// Sign implements the crypto.Signer interface
func (priv *PrivateKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) (signature []byte, err error) {
	if pssOpts, ok := opts.(*cryptoRSA.PSSOptions); ok {
		return cryptoRSA.SignPSS(rand, priv.Into(), pssOpts.Hash, digest, pssOpts)
	}

	return SignPKCS1v15(rand, priv, sm.Hash{Hash: opts.HashFunc()}, digest)
}

func (priv *PrivateKey) Public() crypto.PublicKey {
	return &priv.PublicKey
}