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Split constant time functions into crypto/subtle.

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R=rsc
CC=go-dev
http://go/go-review/1018020
This commit is contained in:
Adam Langley 2009-11-02 11:12:07 -08:00
parent d00248980b
commit ad67a86626
8 changed files with 249 additions and 216 deletions
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79
src/pkg/crypto/rsa/rsa.go
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@ -8,11 +8,12 @@ package rsa
// TODO(agl): Add support for PSS padding.
import (
"bytes";
big "gmp";
"hash";
"io";
"os";
"bytes";
"crypto/subtle";
big "gmp";
"hash";
"io";
"os";
)
var bigOne = big.NewInt(1)
@ -92,7 +93,7 @@ type PublicKey struct {
// A PrivateKey represents an RSA key
type PrivateKey struct {
PublicKey; // public part.
PublicKey; // public part.
D *big.Int; // private exponent
P, Q *big.Int; // prime factors of N
}
@ -300,58 +301,6 @@ func modInverse(a, n *big.Int) (ia *big.Int) {
return x;
}
// constantTimeCompare returns 1 iff the two equal length slices, x
// and y, have equal contents. The time taken is a function of the length of
// the slices and is independent of the contents.
func constantTimeCompare(x, y []byte) int {
var v byte;
for i := 0; i < len(x); i++ {
v |= x[i]^y[i];
}
return constantTimeByteEq(v, 0);
}
// constantTimeSelect returns a if v is 1 and b if v is 0.
// Its behaviour is undefined if v takes any other value.
func constantTimeSelect(v, a, b int) int {
return ^(v-1)&a | (v-1)&b;
}
// constantTimeByteEq returns 1 if a == b and 0 otherwise.
func constantTimeByteEq(a, b uint8) int {
x := ^(a^b);
x &= x>>4;
x &= x>>2;
x &= x>>1;
return int(x);
}
// constantTimeEq returns 1 if a == b and 0 otherwise.
func constantTimeEq(a, b int32) int {
x := ^(a^b);
x &= x>>16;
x &= x>>8;
x &= x>>4;
x &= x>>2;
x &= x>>1;
return int(x&1);
}
// constantTimeCopy copies the contents of y into x iff v == 1. If v == 0, x is left unchanged.
// Its behaviour is undefined if v takes any other value.
func constantTimeCopy(v int, x, y []byte) {
xmask := byte(v - 1);
ymask := byte(^(v - 1));
for i := 0; i < len(x); i++ {
x[i] = x[i] & xmask | y[i] & ymask;
}
return;
}
// 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) {
@ -419,7 +368,7 @@ func DecryptOAEP(hash hash.Hash, rand io.Reader, priv *PrivateKey, ciphertext []
// anything about this.)
em := leftPad(m.Bytes(), k);
firstByteIsZero := constantTimeByteEq(em[0], 0);
firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0);
seed := em[1 : hash.Size() + 1];
db := em[hash.Size() + 1 : len(em)];
@ -433,7 +382,7 @@ func DecryptOAEP(hash hash.Hash, rand io.Reader, priv *PrivateKey, ciphertext []
// 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 := constantTimeCompare(lHash, lHash2);
lHash2Good := subtle.ConstantTimeCompare(lHash, lHash2);
// The remainder of the plaintext must be zero or more 0x00, followed
// by 0x01, followed by the message.
@ -445,11 +394,11 @@ func DecryptOAEP(hash hash.Hash, rand io.Reader, priv *PrivateKey, ciphertext []
rest := db[hash.Size() : len(db)];
for i := 0; i < len(rest); i++ {
equals0 := constantTimeByteEq(rest[i], 0);
equals1 := constantTimeByteEq(rest[i], 1);
index = constantTimeSelect(lookingForIndex & equals1, i, index);
lookingForIndex = constantTimeSelect(equals1, 0, lookingForIndex);
invalid = constantTimeSelect(lookingForIndex & ^equals0, 1, invalid);
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 {