Golang Int.Mod方法代码示例

// powerOffset computes the offset by (n + 2^exp) % (2^mod)
func powerOffset(id []byte, exp int, mod int) []byte {
	// Copy the existing slice
	off := make([]byte, len(id))
	copy(off, id)

	// Convert the ID to a bigint
	idInt := big.Int{}
	idInt.SetBytes(id)

	// Get the offset
	two := big.NewInt(2)
	offset := big.Int{}
	offset.Exp(two, big.NewInt(int64(exp)), nil)

	// Sum
	sum := big.Int{}
	sum.Add(&idInt, &offset)

	// Get the ceiling
	ceil := big.Int{}
	ceil.Exp(two, big.NewInt(int64(mod)), nil)

	// Apply the mod
	idInt.Mod(&sum, &ceil)

	// Add together
	return idInt.Bytes()
}

func (c *Conversation) processSMP1(mpis []*big.Int) error {
	if len(mpis) != 6 {
		return errors.New("otr: incorrect number of arguments in SMP1 message")
	}
	g2a := mpis[0]
	c2 := mpis[1]
	d2 := mpis[2]
	g3a := mpis[3]
	c3 := mpis[4]
	d3 := mpis[5]
	h := sha256.New()

	r := new(big.Int).Exp(g, d2, p)
	s := new(big.Int).Exp(g2a, c2, p)
	r.Mul(r, s)
	r.Mod(r, p)
	t := new(big.Int).SetBytes(hashMPIs(h, 1, r))
	if c2.Cmp(t) != 0 {
		return errors.New("otr: ZKP c2 incorrect in SMP1 message")
	}
	r.Exp(g, d3, p)
	s.Exp(g3a, c3, p)
	r.Mul(r, s)
	r.Mod(r, p)
	t.SetBytes(hashMPIs(h, 2, r))
	if c3.Cmp(t) != 0 {
		return errors.New("otr: ZKP c3 incorrect in SMP1 message")
	}

	c.smp.g2a = g2a
	c.smp.g3a = g3a
	return nil
}

func plus(z *big.Int, x *big.Int, y *big.Int) *big.Int {
	var lim big.Int
	lim.Exp(big.NewInt(2), big.NewInt(256), big.NewInt(0))
	z.Add(x, y)
	return z.Mod(z, &lim)

}

// 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 {
		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
}

// signRFC6979 generates a deterministic ECDSA signature according to RFC 6979
// and BIP 62.
func signRFC6979(privateKey *PrivateKey, hash []byte) (*Signature, error) {

	privkey := privateKey.ToECDSA()
	N := order
	k := NonceRFC6979(privkey.D, hash, nil, nil)
	inv := new(big.Int).ModInverse(k, N)
	r, _ := privkey.Curve.ScalarBaseMult(k.Bytes())
	if r.Cmp(N) == 1 {
		r.Sub(r, N)
	}

	if r.Sign() == 0 {
		return nil, errors.New("calculated R is zero")
	}

	e := hashToInt(hash, privkey.Curve)
	s := new(big.Int).Mul(privkey.D, r)
	s.Add(s, e)
	s.Mul(s, inv)
	s.Mod(s, N)

	if s.Cmp(halforder) == 1 {
		s.Sub(N, s)
	}
	if s.Sign() == 0 {
		return nil, errors.New("calculated S is zero")
	}
	return &Signature{R: r, S: s}, nil
}

func gcd2(a, b *big.Int) *big.Int {
	b = newB.Set(b)
	for b.Sign() != 0 {
		a, b = b, a.Mod(a, b)
	}
	return a
}

// schnorrCombineSigs combines a list of partial Schnorr signatures s values
// into a complete signature s for some group public key. This is achieved
// by simply adding the s values of the partial signatures as scalars.
func schnorrCombineSigs(curve *secp256k1.KoblitzCurve, sigss [][]byte) (*big.Int,
	error) {
	combinedSigS := new(big.Int).SetInt64(0)
	for i, sigs := range sigss {
		sigsBI := EncodedBytesToBigInt(copyBytes(sigs))
		if sigsBI.Cmp(bigZero) == 0 {
			str := fmt.Sprintf("sig s %v is zero", i)
			return nil, schnorrError(ErrInputValue, str)
		}
		if sigsBI.Cmp(curve.N) >= 0 {
			str := fmt.Sprintf("sig s %v is out of bounds", i)
			return nil, schnorrError(ErrInputValue, str)
		}

		combinedSigS.Add(combinedSigS, sigsBI)
		combinedSigS.Mod(combinedSigS, curve.N)
	}

	if combinedSigS.Cmp(bigZero) == 0 {
		str := fmt.Sprintf("combined sig s %v is zero", combinedSigS)
		return nil, schnorrError(ErrZeroSigS, str)
	}

	return combinedSigS, nil
}

// Decrypt takes two integers, resulting from an ElGamal encryption, and
// returns the plaintext of the message. An error can result only if the
// ciphertext is invalid. Users should keep in mind that this is a padding
// oracle and thus, if exposed to an adaptive chosen ciphertext attack, can
// be used to break the cryptosystem.  See ``Chosen Ciphertext Attacks
// Against Protocols Based on the RSA Encryption Standard PKCS #1'', Daniel
// Bleichenbacher, Advances in Cryptology (Crypto '98),
func Decrypt(priv *PrivateKey, c1, c2 *big.Int) (msg []byte, err error) {
	s := new(big.Int).Exp(c1, priv.X, priv.P)
	s.ModInverse(s, priv.P)
	s.Mul(s, c2)
	s.Mod(s, priv.P)
	em := s.Bytes()

	firstByteIsTwo := subtle.ConstantTimeByteEq(em[0], 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.
	var lookingForIndex, index int
	lookingForIndex = 1

	for i := 1; i < len(em); i++ {
		equals0 := subtle.ConstantTimeByteEq(em[i], 0)
		index = subtle.ConstantTimeSelect(lookingForIndex&equals0, i, index)
		lookingForIndex = subtle.ConstantTimeSelect(equals0, 0, lookingForIndex)
	}

	if firstByteIsTwo != 1 || lookingForIndex != 0 || index < 9 {
		return nil, errors.New("elgamal: decryption error")
	}
	return em[index+1:], nil
}

// Adapted from from crypto/rsa decrypt
func blind(random io.Reader, key *rsa.PublicKey, c *big.Int) (blinded, unblinder *big.Int, err error) {
	// Blinding enabled. Blinding involves multiplying c by r^e.
	// Then the decryption operation performs (m^e * r^e)^d mod n
	// which equals mr mod n. The factor of r can then be removed
	// by multiplying by the multiplicative inverse of r.

	var r *big.Int

	for {
		r, err = rand.Int(random, key.N)
		if err != nil {
			return
		}
		if r.Cmp(bigZero) == 0 {
			r = bigOne
		}
		ir, ok := modInverse(r, key.N)
		if ok {
			bigE := big.NewInt(int64(key.E))
			rpowe := new(big.Int).Exp(r, bigE, key.N)
			cCopy := new(big.Int).Set(c)
			cCopy.Mul(cCopy, rpowe)
			cCopy.Mod(cCopy, key.N)
			return cCopy, ir, nil
		}
	}
}

// ComputeKey computes the session key given the salt and the value of B.
func (cs *ClientSession) ComputeKey(salt, B []byte) ([]byte, error) {
	cs.salt = salt

	err := cs.setB(B)
	if err != nil {
		return nil, err
	}

	// x = H(s, p)                 (user enters password)
	x := new(big.Int).SetBytes(cs.SRP.KeyDerivationFunc(cs.salt, cs.password))

	// S = (B - kg^x) ^ (a + ux)   (computes session key)
	// t1 = g^x
	t1 := new(big.Int).Exp(cs.SRP.Group.Generator, x, cs.SRP.Group.Prime)
	// unblind verifier
	t1.Sub(cs.SRP.Group.Prime, t1)
	t1.Mul(cs.SRP._k, t1)
	t1.Add(t1, cs._B)
	t1.Mod(t1, cs.SRP.Group.Prime)

	// t2 = ux
	t2 := new(big.Int).Mul(cs._u, x)
	// t2 = a + ux
	t2.Add(cs._a, t2)

	// t1 = (B - kg^x) ^ (a + ux)
	t3 := new(big.Int).Exp(t1, t2, cs.SRP.Group.Prime)
	// K = H(S)
	cs.key = quickHash(cs.SRP.HashFunc, t3.Bytes())

	return cs.key, nil
}

func main() {

	var iban string
	var r, s, t, st []string
	u := new(big.Int)
	v := new(big.Int)
	w := new(big.Int)

	iban = "GB82 TEST 1234 5698 7654 32"
	r = strings.Split(iban, " ")
	s = strings.Split(r[0], "")
	t = strings.Split(r[1], "")

	st = []string{strconv.Itoa(sCode[t[0]]),
		strconv.Itoa(sCode[t[1]]),
		strconv.Itoa(sCode[t[2]]),
		strconv.Itoa(sCode[t[3]]),
		strings.Join(r[2:6], ""),
		strconv.Itoa(sCode[s[0]]),
		strconv.Itoa(sCode[s[1]]),
		strings.Join(s[2:4], ""),
	}

	u.SetString(strings.Join(st, ""), 10)
	v.SetInt64(97)
	w.Mod(u, v)

	if w.Uint64() == 1 && lCode[strings.Join(s[0:2], "")] == len(strings.Join(r, "")) {
		fmt.Printf("IBAN %s looks good!\n", iban)
	} else {
		fmt.Printf("IBAN %s looks wrong!\n", iban)
	}
}

func main() {
	lim := 1000
	primes := allPrimes(lim)
	mx_cyc := 0
	mx_len := 0

	for _, i := range primes {
		j := 1
		for j < i {
			p := new(big.Int)
			*p = bigPow(10, j)
			res := new(big.Int)
			res.Mod(p, big.NewInt(int64(i)))
			if res.Int64() == 1 {
				if mx_len < j {
					mx_len = i
					mx_cyc = j
				}
				break
			}
			j++
		}
	}
	fmt.Printf("Found: 1/%d yields %d cycles\n", mx_len, mx_cyc)
}

func main() {
	filename := "rosalind_pper.txt"
	b, err := ioutil.ReadFile(filename)
	if err != nil {
		fmt.Printf("Error is %s", err.Error())
		os.Exit(1)
	}

	input := string(b)
	lines := strings.Split(input, "\n")[0]

	tokens := strings.Split(lines, " ")
	fmt.Println(tokens)

	totalVals, _ := strconv.ParseInt(tokens[0], 10, 64)
	numSelections, _ := strconv.ParseInt(tokens[1], 10, 64)

	min = totalVals - numSelections + 1

	result := Factorial(big.NewInt(totalVals))
	//fmt.Println(result)

	var mod big.Int

	mod.Mod(result, big.NewInt(1000000))

	fmt.Println(&mod)
}

/*
	The Join function
	The first fuction to be executed
	Alaows it gives the hash and id and request the finger table for the boost node
*/
func Join(test bool) { //

	//generate id
	me.nodeId = Index(generateNodeId(), BITS)
	nodeIdInt := me.nodeId
	me.storage = map[string]string{}

	//prepare finger table
	if test { //firstnode in the ring
		me.offset = 0
		for i, _ := range me.FingerTable {
			//compute the ith node
			two := big.NewInt(2)
			dist := big.Int{}
			dist.Exp(two, big.NewInt(int64(i)), nil)
			var ithNode big.Int
			ithNode.Add(&dist, &nodeIdInt)
			x := ringSize(BITS)
			ithNode.Mod(&ithNode, &x)
			//fill the fingr table row
			me.FingerTable[i][0] = ithNode.String()
			me.FingerTable[i][1] = me.nodeId.String()
			me.FingerTable[i][2] = me.address //this node address
		}
	} else { //not first node in the ring
		//initialize offset
		GetOffsetClient(me.target)
		updateFingerTable(nodeIdInt, me.target) //target server required
		go infornMySuccessor()
		go AutoUpdate() // initialize auto update
	}

}

// (n + 2^(k-1)) mod (2^m)
func calcFinger(n []byte, k int, m int) (string, []byte) {

	// convert the n to a bigint
	nBigInt := big.Int{}
	nBigInt.SetBytes(n)

	// get the right addend, i.e. 2^(k-1)
	two := big.NewInt(2)
	addend := big.Int{}
	addend.Exp(two, big.NewInt(int64(k-1)), nil)

	// calculate sum
	sum := big.Int{}
	sum.Add(&nBigInt, &addend)

	// calculate 2^m
	ceil := big.Int{}
	ceil.Exp(two, big.NewInt(int64(m)), nil)

	// apply the mod
	result := big.Int{}
	result.Mod(&sum, &ceil)

	resultBytes := result.Bytes()
	resultHex := fmt.Sprintf("%x", resultBytes)

	return resultHex, resultBytes
}