Imported Upstream version 60upstream/60

1 files changed, 502 insertions, 0 deletions

diff --git a/src/pkg/crypto/rsa/rsa.go b/src/pkg/crypto/rsa/rsa.go
new file mode 100644
index 000000000..6957659f2
--- /dev/null
+++ b/src/pkg/crypto/rsa/rsa.go
@@ -0,0 +1,502 @@
+// 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.
+package rsa
+
+// TODO(agl): Add support for PSS padding.
+
+import (
+	"big"
+	"crypto/rand"
+	"crypto/subtle"
+	"hash"
+	"io"
+	"os"
+)
+
+var bigZero = big.NewInt(0)
+var bigOne = big.NewInt(1)
+
+// A PublicKey represents the public part of an RSA key.
+type PublicKey struct {
+	N *big.Int // modulus
+	E int      // public exponent
+}
+
+// A PrivateKey represents an RSA key
+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
+}
+
+type PrecomputedValues struct {
+	Dp, Dq *big.Int // D mod (P-1) (or mod Q-1) 
+	Qinv   *big.Int // Q^-1 mod Q
+
+	// 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 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).
+}
+
+// Validate performs basic sanity checks on the key.
+// It returns nil if the key is valid, or else an os.Error describing a problem.
+
+func (priv *PrivateKey) Validate() os.Error {
+	// Check that the prime factors are actually prime. Note that this is
+	// just a sanity check. Since the random witnesses chosen by
+	// ProbablyPrime are deterministic, given the candidate number, it's
+	// easy for an attack to generate composites that pass this test.
+	for _, prime := range priv.Primes {
+		if !big.ProbablyPrime(prime, 20) {
+			return os.NewError("prime factor is composite")
+		}
+	}
+
+	// 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 os.NewError("invalid modulus")
+	}
+	// Check that e and totient(Πprimes) are coprime.
+	totient := new(big.Int).Set(bigOne)
+	for _, prime := range priv.Primes {
+		pminus1 := new(big.Int).Sub(prime, bigOne)
+		totient.Mul(totient, pminus1)
+	}
+	e := big.NewInt(int64(priv.E))
+	gcd := new(big.Int)
+	x := new(big.Int)
+	y := new(big.Int)
+	big.GcdInt(gcd, x, y, totient, e)
+	if gcd.Cmp(bigOne) != 0 {
+		return os.NewError("invalid public exponent E")
+	}
+	// Check that de ≡ 1 (mod totient(Πprimes))
+	de := new(big.Int).Mul(priv.D, e)
+	de.Mod(de, totient)
+	if de.Cmp(bigOne) != 0 {
+		return os.NewError("invalid private exponent D")
+	}
+	return nil
+}
+
+// GenerateKey generates an RSA keypair of the given bit size.
+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
+// size, as suggested in [1]. Although the public keys are compatible
+// (actually, indistinguishable) from the 2-prime case, the private keys are
+// not. Thus it may not be possible to export multi-prime private keys in
+// certain formats or to subsequently import them into other code.
+//
+// Table 1 in [2] suggests maximum numbers of primes for a given size.
+//
+// [1] US patent 4405829 (1972, expired)
+// [2] http://www.cacr.math.uwaterloo.ca/techreports/2006/cacr2006-16.pdf
+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
+	// (p-1)(q-1), the smallest possible value is 3. Some have
+	// suggested that a larger exponent (often 2**16+1) be used
+	// since previous implementation bugs[1] were avoided when this
+	// was the case. However, there are no current reasons not to use
+	// small exponents.
+	// [1] http://marc.info/?l=cryptography&m=115694833312008&w=2
+	priv.E = 3
+
+	if nprimes < 2 {
+		return nil, os.NewError("rsa.GenerateMultiPrimeKey: nprimes must be >= 2")
+	}
+
+	primes := make([]*big.Int, nprimes)
+
+NextSetOfPrimes:
+	for {
+		todo := bits
+		for i := 0; i < nprimes; i++ {
+			primes[i], err = rand.Prime(random, todo/(nprimes-i))
+			if err != nil {
+				return nil, err
+			}
+			todo -= primes[i].BitLen()
+		}
+
+		// Make sure that primes is pairwise unequal.
+		for i, prime := range primes {
+			for j := 0; j < i; j++ {
+				if prime.Cmp(primes[j]) == 0 {
+					continue NextSetOfPrimes
+				}
+			}
+		}
+
+		n := new(big.Int).Set(bigOne)
+		totient := new(big.Int).Set(bigOne)
+		pminus1 := new(big.Int)
+		for _, prime := range primes {
+			n.Mul(n, prime)
+			pminus1.Sub(prime, bigOne)
+			totient.Mul(totient, pminus1)
+		}
+
+		g := new(big.Int)
+		priv.D = new(big.Int)
+		y := new(big.Int)
+		e := big.NewInt(int64(priv.E))
+		big.GcdInt(g, priv.D, y, e, totient)
+
+		if g.Cmp(bigOne) == 0 {
+			priv.D.Add(priv.D, totient)
+			priv.Primes = primes
+			priv.N = n
+
+			break
+		}
+	}
+
+	priv.Precompute()
+	return
+}
+
+// incCounter increments a four byte, big-endian counter.
+func incCounter(c *[4]byte) {
+	if c[3]++; c[3] != 0 {
+		return
+	}
+	if c[2]++; c[2] != 0 {
+		return
+	}
+	if c[1]++; c[1] != 0 {
+		return
+	}
+	c[0]++
+}
+
+// mgf1XOR XORs the bytes in out with a mask generated using the MGF1 function
+// specified in PKCS#1 v2.1.
+func mgf1XOR(out []byte, hash hash.Hash, seed []byte) {
+	var counter [4]byte
+
+	done := 0
+	for done < len(out) {
+		hash.Write(seed)
+		hash.Write(counter[0:4])
+		digest := hash.Sum()
+		hash.Reset()
+
+		for i := 0; i < len(digest) && done < len(out); i++ {
+			out[done] ^= digest[i]
+			done++
+		}
+		incCounter(&counter)
+	}
+}
+
+// MessageTooLongError is returned when attempting to encrypt a message which
+// is too large for the size of the public key.
+type MessageTooLongError struct{}
+
+func (MessageTooLongError) String() string {
+	return "message too long for RSA public key size"
+}
+
+func encrypt(c *big.Int, pub *PublicKey, m *big.Int) *big.Int {
+	e := big.NewInt(int64(pub.E))
+	c.Exp(m, e, pub.N)
+	return c
+}
+
+// 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, 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 {
+		err = MessageTooLongError{}
+		return
+	}
+
+	hash.Write(label)
+	lHash := hash.Sum()
+	hash.Reset()
+
+	em := make([]byte, k)
+	seed := em[1 : 1+hash.Size()]
+	db := em[1+hash.Size():]
+
+	copy(db[0:hash.Size()], lHash)
+	db[len(db)-len(msg)-1] = 1
+	copy(db[len(db)-len(msg):], msg)
+
+	_, err = io.ReadFull(random, seed)
+	if err != nil {
+		return
+	}
+
+	mgf1XOR(db, hash, seed)
+	mgf1XOR(seed, hash, db)
+
+	m := new(big.Int)
+	m.SetBytes(em)
+	c := encrypt(new(big.Int), pub, m)
+	out = c.Bytes()
+
+	if len(out) < k {
+		// If the output is too small, we need to left-pad with zeros.
+		t := make([]byte, k)
+		copy(t[k-len(out):], out)
+		out = t
+	}
+
+	return
+}
+
+// A DecryptionError represents a failure to decrypt a message.
+// It is deliberately vague to avoid adaptive attacks.
+type DecryptionError struct{}
+
+func (DecryptionError) String() string { return "RSA decryption error" }
+
+// A VerificationError represents a failure to verify a signature.
+// It is deliberately vague to avoid adaptive attacks.
+type VerificationError struct{}
+
+func (VerificationError) String() string { return "RSA verification error" }
+
+// modInverse returns ia, the inverse of a in the multiplicative group of prime
+// order n. It requires that a be a member of the group (i.e. less than n).
+func modInverse(a, n *big.Int) (ia *big.Int, ok bool) {
+	g := new(big.Int)
+	x := new(big.Int)
+	y := new(big.Int)
+	big.GcdInt(g, x, y, a, n)
+	if g.Cmp(bigOne) != 0 {
+		// In this case, a and n aren't coprime and we cannot calculate
+		// the inverse. This happens because the values of n are nearly
+		// prime (being the product of two primes) rather than truly
+		// prime.
+		return
+	}
+
+	if x.Cmp(bigOne) < 0 {
+		// 0 is not the multiplicative inverse of any element so, if x
+		// < 1, then x is negative.
+		x.Add(x, n)
+	}
+
+	return x, true
+}
+
+// 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)
+	}
+}
+
+// decrypt performs an RSA decryption, resulting in a plaintext integer. If a
+// random source is given, RSA blinding is used.
+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{}
+		return
+	}
+
+	var ir *big.Int
+	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
+		// by multiplying by the multiplicative inverse of r.
+
+		var r *big.Int
+
+		for {
+			r, err = rand.Int(random, priv.N)
+			if err != nil {
+				return
+			}
+			if r.Cmp(bigZero) == 0 {
+				r = bigOne
+			}
+			var ok bool
+			ir, ok = modInverse(r, priv.N)
+			if ok {
+				break
+			}
+		}
+		bigE := big.NewInt(int64(priv.E))
+		rpowe := new(big.Int).Exp(r, bigE, priv.N)
+		cCopy := new(big.Int).Set(c)
+		cCopy.Mul(cCopy, rpowe)
+		cCopy.Mod(cCopy, priv.N)
+		c = cCopy
+	}
+
+	if priv.Precomputed.Dp == nil {
+		m = new(big.Int).Exp(c, priv.D, priv.N)
+	} else {
+		// We have the precalculated values needed for the CRT.
+		m = new(big.Int).Exp(c, priv.Precomputed.Dp, priv.Primes[0])
+		m2 := new(big.Int).Exp(c, priv.Precomputed.Dq, priv.Primes[1])
+		m.Sub(m, m2)
+		if m.Sign() < 0 {
+			m.Add(m, priv.Primes[0])
+		}
+		m.Mul(m, priv.Precomputed.Qinv)
+		m.Mod(m, priv.Primes[0])
+		m.Mul(m, priv.Primes[1])
+		m.Add(m, m2)
+
+		for i, values := range priv.Precomputed.CRTValues {
+			prime := priv.Primes[2+i]
+			m2.Exp(c, values.Exp, prime)
+			m2.Sub(m2, m)
+			m2.Mul(m2, values.Coeff)
+			m2.Mod(m2, prime)
+			if m2.Sign() < 0 {
+				m2.Add(m2, prime)
+			}
+			m2.Mul(m2, values.R)
+			m.Add(m, m2)
+		}
+	}
+
+	if ir != nil {
+		// Unblind.
+		m.Mul(m, ir)
+		m.Mod(m, priv.N)
+	}
+
+	return
+}
+
+// DecryptOAEP decrypts ciphertext using RSA-OAEP.
+// If rand != nil, DecryptOAEP uses RSA blinding to avoid timing side-channel attacks.
+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 {
+		err = DecryptionError{}
+		return
+	}
+
+	c := new(big.Int).SetBytes(ciphertext)
+
+	m, err := decrypt(random, priv, c)
+	if err != nil {
+		return
+	}
+
+	hash.Write(label)
+	lHash := hash.Sum()
+	hash.Reset()
+
+	// Converting the plaintext number to bytes will strip any
+	// leading zeros so we may have to left pad. We do this unconditionally
+	// to avoid leaking timing information. (Although we still probably
+	// leak the number of leading zeros. It's not clear that we can do
+	// anything about this.)
+	em := leftPad(m.Bytes(), k)
+
+	firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0)
+
+	seed := em[1 : hash.Size()+1]
+	db := em[hash.Size()+1:]
+
+	mgf1XOR(seed, hash, db)
+	mgf1XOR(db, hash, seed)
+
+	lHash2 := db[0:hash.Size()]
+
+	// We have to validate the plaintext in constant time in order to avoid
+	// attacks like: J. Manger. A Chosen Ciphertext Attack on RSA Optimal
+	// Asymmetric Encryption Padding (OAEP) as Standardized in PKCS #1
+	// v2.0. In J. Kilian, editor, Advances in Cryptology.
+	lHash2Good := subtle.ConstantTimeCompare(lHash, lHash2)
+
+	// The remainder of the plaintext must be zero or more 0x00, followed
+	// by 0x01, followed by the message.
+	//   lookingForIndex: 1 iff we are still looking for the 0x01
+	//   index: the offset of the first 0x01 byte
+	//   invalid: 1 iff we saw a non-zero byte before the 0x01.
+	var lookingForIndex, index, invalid int
+	lookingForIndex = 1
+	rest := db[hash.Size():]
+
+	for i := 0; i < len(rest); i++ {
+		equals0 := subtle.ConstantTimeByteEq(rest[i], 0)
+		equals1 := subtle.ConstantTimeByteEq(rest[i], 1)
+		index = subtle.ConstantTimeSelect(lookingForIndex&equals1, i, index)
+		lookingForIndex = subtle.ConstantTimeSelect(equals1, 0, lookingForIndex)
+		invalid = subtle.ConstantTimeSelect(lookingForIndex&^equals0, 1, invalid)
+	}
+
+	if firstByteIsZero&lHash2Good&^invalid&^lookingForIndex != 1 {
+		err = DecryptionError{}
+		return
+	}
+
+	msg = rest[index+1:]
+	return
+}
+
+// leftPad returns a new slice of length size. The contents of input are right
+// aligned in the new slice.
+func leftPad(input []byte, size int) (out []byte) {
+	n := len(input)
+	if n > size {
+		n = size
+	}
+	out = make([]byte, size)
+	copy(out[len(out)-n:], input)
+	return
+}