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crypto/rand: add utility functions for number generation

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This code is extracted from crypto/rsa with
a few variables renamed and a comment fixed.

R=agl, rsc, agl
CC=golang-dev
https://golang.org/cl/4446068
This commit is contained in:
Anthony Martin 2011-05-18 18:55:06 -07:00 committed by Adam Langley
parent 4ffff35abd
commit 24b2f48a4a
3 changed files with 93 additions and 74 deletions
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1
src/pkg/crypto/rand/Makefile
View File

@ -8,6 +8,7 @@ TARG=crypto/rand
GOFILES=\
rand.go\
util.go\
GOFILES_freebsd=\
rand_unix.go\

80
src/pkg/crypto/rand/util.go Normal file
View File

@ -0,0 +1,80 @@
// Copyright 2011 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 rand
import (
"big"
"io"
"os"
)
// Prime returns a number, p, of the given size, such that p is prime
// with high probability.
func Prime(rand io.Reader, bits int) (p *big.Int, err os.Error) {
if bits < 1 {
err = os.EINVAL
}
b := uint(bits % 8)
if b == 0 {
b = 8
}
bytes := make([]byte, (bits+7)/8)
p = new(big.Int)
for {
_, err = io.ReadFull(rand, bytes)
if err != nil {
return nil, err
}
// Clear bits in the first byte to make sure the candidate has a size <= bits.
bytes[0] &= uint8(int(1<<b) - 1)
// Don't let the value be too small, i.e, set the most significant bit.
bytes[0] |= 1 << (b - 1)
// Make the value odd since an even number this large certainly isn't prime.
bytes[len(bytes)-1] |= 1
p.SetBytes(bytes)
if big.ProbablyPrime(p, 20) {
return
}
}
return
}
// Int returns a uniform random value in [0, max).
func Int(rand io.Reader, max *big.Int) (n *big.Int, err os.Error) {
k := (max.BitLen() + 7) / 8
// b is the number of bits in the most significant byte of max.
b := uint(max.BitLen() % 8)
if b == 0 {
b = 8
}
bytes := make([]byte, k)
n = new(big.Int)
for {
_, err = io.ReadFull(rand, bytes)
if err != nil {
return nil, err
}
// Clear bits in the first byte to increase the probability
// that the candidate is < max.
bytes[0] &= uint8(int(1<<b) - 1)
n.SetBytes(bytes)
if n.Cmp(max) < 0 {
return
}
}
return
}

86
src/pkg/crypto/rsa/rsa.go
View File

@ -9,6 +9,7 @@ package rsa
import (
"big"
"crypto/rand"
"crypto/subtle"
"hash"
"io"
@ -18,69 +19,6 @@ import (
var bigZero = big.NewInt(0)
var bigOne = big.NewInt(1)
// randomPrime returns a number, p, of the given size, such that p is prime
// with high probability.
func randomPrime(rand io.Reader, bits int) (p *big.Int, err os.Error) {
if bits < 1 {
err = os.EINVAL
}
bytes := make([]byte, (bits+7)/8)
p = new(big.Int)
for {
_, err = io.ReadFull(rand, bytes)
if err != nil {
return
}
// Don't let the value be too small.
bytes[0] |= 0x80
// Make the value odd since an even number this large certainly isn't prime.
bytes[len(bytes)-1] |= 1
p.SetBytes(bytes)
if big.ProbablyPrime(p, 20) {
return
}
}
return
}
// randomNumber returns a uniform random value in [0, max).
func randomNumber(rand io.Reader, max *big.Int) (n *big.Int, err os.Error) {
k := (max.BitLen() + 7) / 8
// r is the number of bits in the used in the most significant byte of
// max.
r := uint(max.BitLen() % 8)
if r == 0 {
r = 8
}
bytes := make([]byte, k)
n = new(big.Int)
for {
_, err = io.ReadFull(rand, bytes)
if err != nil {
return
}
// Clear bits in the first byte to increase the probability
// that the candidate is < max.
bytes[0] &= uint8(int(1<<r) - 1)
n.SetBytes(bytes)
if n.Cmp(max) < 0 {
return
}
}
return
}
// A PublicKey represents the public part of an RSA key.
type PublicKey struct {
N *big.Int // modulus
@ -162,8 +100,8 @@ func (priv *PrivateKey) Validate() os.Error {
}
// GenerateKey generates an RSA keypair of the given bit size.
func GenerateKey(rand io.Reader, bits int) (priv *PrivateKey, err os.Error) {
return GenerateMultiPrimeKey(rand, 2, bits)
func GenerateKey(random io.Reader, bits int) (priv *PrivateKey, err os.Error) {
return GenerateMultiPrimeKey(random, 2, bits)
}
// GenerateMultiPrimeKey generates a multi-prime RSA keypair of the given bit
@ -176,7 +114,7 @@ func GenerateKey(rand io.Reader, bits int) (priv *PrivateKey, err os.Error) {
//
// [1] US patent 4405829 (1972, expired)
// [2] http://www.cacr.math.uwaterloo.ca/techreports/2006/cacr2006-16.pdf
func GenerateMultiPrimeKey(rand io.Reader, nprimes int, bits int) (priv *PrivateKey, err os.Error) {
func GenerateMultiPrimeKey(random io.Reader, nprimes int, bits int) (priv *PrivateKey, err os.Error) {
priv = new(PrivateKey)
// Smaller public exponents lead to faster public key
// operations. Since the exponent must be coprime to
@ -198,7 +136,7 @@ NextSetOfPrimes:
for {
todo := bits
for i := 0; i < nprimes; i++ {
primes[i], err = randomPrime(rand, todo/(nprimes-i))
primes[i], err = rand.Prime(random, todo/(nprimes-i))
if err != nil {
return nil, err
}
@ -293,7 +231,7 @@ func encrypt(c *big.Int, pub *PublicKey, m *big.Int) *big.Int {
// EncryptOAEP encrypts the given message with RSA-OAEP.
// The message must be no longer than the length of the public modulus less
// twice the hash length plus 2.
func EncryptOAEP(hash hash.Hash, rand io.Reader, pub *PublicKey, msg []byte, label []byte) (out []byte, err os.Error) {
func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, label []byte) (out []byte, err os.Error) {
hash.Reset()
k := (pub.N.BitLen() + 7) / 8
if len(msg) > k-2*hash.Size()-2 {
@ -313,7 +251,7 @@ func EncryptOAEP(hash hash.Hash, rand io.Reader, pub *PublicKey, msg []byte, lab
db[len(db)-len(msg)-1] = 1
copy(db[len(db)-len(msg):], msg)
_, err = io.ReadFull(rand, seed)
_, err = io.ReadFull(random, seed)
if err != nil {
return
}
@ -405,7 +343,7 @@ func (priv *PrivateKey) Precompute() {
// decrypt performs an RSA decryption, resulting in a plaintext integer. If a
// random source is given, RSA blinding is used.
func decrypt(rand io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.Error) {
func decrypt(random io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.Error) {
// TODO(agl): can we get away with reusing blinds?
if c.Cmp(priv.N) > 0 {
err = DecryptionError{}
@ -413,7 +351,7 @@ func decrypt(rand io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.E
}
var ir *big.Int
if rand != nil {
if random != nil {
// 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
@ -422,7 +360,7 @@ func decrypt(rand io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.E
var r *big.Int
for {
r, err = randomNumber(rand, priv.N)
r, err = rand.Int(random, priv.N)
if err != nil {
return
}
@ -483,7 +421,7 @@ func decrypt(rand io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.E
// DecryptOAEP decrypts ciphertext using RSA-OAEP.
// If rand != nil, DecryptOAEP uses RSA blinding to avoid timing side-channel attacks.
func DecryptOAEP(hash hash.Hash, rand io.Reader, priv *PrivateKey, ciphertext []byte, label []byte) (msg []byte, err os.Error) {
func DecryptOAEP(hash hash.Hash, random io.Reader, priv *PrivateKey, ciphertext []byte, label []byte) (msg []byte, err os.Error) {
k := (priv.N.BitLen() + 7) / 8
if len(ciphertext) > k ||
k < hash.Size()*2+2 {
@ -493,7 +431,7 @@ func DecryptOAEP(hash hash.Hash, rand io.Reader, priv *PrivateKey, ciphertext []
c := new(big.Int).SetBytes(ciphertext)
m, err := decrypt(rand, priv, c)
m, err := decrypt(random, priv, c)
if err != nil {
return
}