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crypto/rsa: add support for precomputing CRT values.

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This speeds up private key operations by 3.5x (for a 2048-bit
modulus).

R=golang-dev, r, rsc1
CC=golang-dev
https://golang.org/cl/4348053
This commit is contained in:
Adam Langley 2011-04-05 18:07:01 -04:00
parent 9f1394d270
commit 360ab50a9b
4 changed files with 98 additions and 19 deletions
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49
src/pkg/crypto/rsa/rsa.go
View file

@ -13,6 +13,7 @@ import (
"hash"
"io"
"os"
"sync"
)
var bigZero = big.NewInt(0)
@ -92,12 +93,16 @@ type PrivateKey struct {
PublicKey // public part.
D *big.Int // private exponent
P, Q *big.Int // prime factors of N
rwMutex sync.RWMutex // protects the following
dP, dQ *big.Int // D mod (P-1) (or mod Q-1)
pInv *big.Int // p^-1 mod 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 {
func (priv *PrivateKey) Validate() os.Error {
// Check that p and q are 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
@ -321,6 +326,18 @@ func modInverse(a, n *big.Int) (ia *big.Int, ok bool) {
return x, true
}
// precompute performs some calculations that speed up private key operations
// in the future.
func (priv *PrivateKey) precompute() {
priv.dP = new(big.Int).Sub(priv.P, bigOne)
priv.dP.Mod(priv.D, priv.dP)
priv.dQ = new(big.Int).Sub(priv.Q, bigOne)
priv.dQ.Mod(priv.D, priv.dQ)
priv.pInv = new(big.Int).ModInverse(priv.P, priv.Q)
}
// 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) {
@ -359,7 +376,35 @@ func decrypt(rand io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int, err os.E
c.Mod(c, priv.N)
}
m = new(big.Int).Exp(c, priv.D, priv.N)
priv.rwMutex.RLock()
if priv.dP == nil && priv.P != nil {
priv.rwMutex.RUnlock()
priv.rwMutex.Lock()
if priv.dP == nil && priv.P != nil {
priv.precompute()
}
priv.rwMutex.Unlock()
priv.rwMutex.RLock()
}
if priv.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.dP, priv.P)
m2 := new(big.Int).Exp(c, priv.dQ, priv.Q)
m2.Sub(m2, m)
if m2.Sign() < 0 {
m2.Add(m2, priv.Q)
}
m2.Mul(m2, priv.pInv)
m2.Mod(m2, priv.Q)
m2.Mul(m2, priv.P)
m.Add(m, m2)
}
priv.rwMutex.RUnlock()
if ir != nil {
// Unblind.