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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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1
src/pkg/Make.deps
View File

@ -17,6 +17,7 @@ crypto/hmac.install: crypto/md5.install crypto/sha1.install hash.install os.inst
crypto/md5.install: hash.install os.install crypto/md5.install: hash.install os.install
crypto/rc4.install: os.install strconv.install crypto/rc4.install: os.install strconv.install
crypto/sha1.install: hash.install os.install crypto/sha1.install: hash.install os.install
crypto/subtle.install:
debug/dwarf.install: encoding/binary.install os.install strconv.install debug/dwarf.install: encoding/binary.install os.install strconv.install
debug/macho.install: bytes.install debug/dwarf.install encoding/binary.install fmt.install io.install os.install strconv.install debug/macho.install: bytes.install debug/dwarf.install encoding/binary.install fmt.install io.install os.install strconv.install
debug/elf.install: debug/dwarf.install encoding/binary.install fmt.install io.install os.install strconv.install debug/elf.install: debug/dwarf.install encoding/binary.install fmt.install io.install os.install strconv.install

1
src/pkg/Makefile
View File

@ -31,6 +31,7 @@ DIRS=\
crypto/md5\ crypto/md5\
crypto/rc4\ crypto/rc4\
crypto/sha1\ crypto/sha1\
crypto/subtle\
debug/dwarf\ debug/dwarf\
debug/macho\ debug/macho\
debug/elf\ debug/elf\

19
src/pkg/crypto/rsa/pkcs1v15.go
View File

@ -6,6 +6,7 @@ package rsa
import ( import (
"bytes"; "bytes";
"crypto/subtle";
big "gmp"; big "gmp";
"io"; "io";
"os"; "os";
@ -27,7 +28,7 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
// EM = 0x02 || PS || 0x00 || M // EM = 0x02 || PS || 0x00 || M
em := make([]byte, k-1); em := make([]byte, k-1);
em[0] = 2; em[0] = 2;
ps, mm := em[1:len(em)-len(msg)-1], em[len(em)-len(msg):len(em)]; ps, mm := em[1 : len(em)-len(msg)-1], em[len(em)-len(msg) : len(em)];
err = nonZeroRandomBytes(ps, rand); err = nonZeroRandomBytes(ps, rand);
if err != nil { if err != nil {
return; return;
@ -77,8 +78,8 @@ func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []by
return; return;
} }
valid &= constantTimeEq(int32(len(msg)), int32(len(key))); valid &= subtle.ConstantTimeEq(int32(len(msg)), int32(len(key)));
constantTimeCopy(valid, key, msg); subtle.ConstantTimeCopy(valid, key, msg);
return; return;
} }
@ -96,8 +97,8 @@ func decryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (valid
} }
em := leftPad(m.Bytes(), k); em := leftPad(m.Bytes(), k);
firstByteIsZero := constantTimeByteEq(em[0], 0); firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0);
secondByteIsTwo := constantTimeByteEq(em[1], 2); secondByteIsTwo := subtle.ConstantTimeByteEq(em[1], 2);
// The remainder of the plaintext must be a string of non-zero random // The remainder of the plaintext must be a string of non-zero random
// octets, followed by a 0, followed by the message. // octets, followed by a 0, followed by the message.
@ -107,9 +108,9 @@ func decryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (valid
lookingForIndex = 1; lookingForIndex = 1;
for i := 2; i < len(em); i++ { for i := 2; i < len(em); i++ {
equals0 := constantTimeByteEq(em[i], 0); equals0 := subtle.ConstantTimeByteEq(em[i], 0);
index = constantTimeSelect(lookingForIndex & equals0, i, index); index = subtle.ConstantTimeSelect(lookingForIndex & equals0, i, index);
lookingForIndex = constantTimeSelect(equals0, 0, lookingForIndex); lookingForIndex = subtle.ConstantTimeSelect(equals0, 0, lookingForIndex);
} }
valid = firstByteIsZero & secondByteIsTwo & (^lookingForIndex & 1); valid = firstByteIsZero & secondByteIsTwo & (^lookingForIndex & 1);
@ -126,7 +127,7 @@ func nonZeroRandomBytes(s []byte, rand io.Reader) (err os.Error) {
for i := 0; i < len(s); i++ { for i := 0; i < len(s); i++ {
for s[i] == 0 { for s[i] == 0 {
_, err = rand.Read(s[i:i+1]); _, err = rand.Read(s[i : i+1]);
if err != nil { if err != nil {
return; return;
} }

79
src/pkg/crypto/rsa/rsa.go
View File

@ -8,11 +8,12 @@ package rsa
// TODO(agl): Add support for PSS padding. // TODO(agl): Add support for PSS padding.
import ( import (
"bytes"; "bytes";
big "gmp"; "crypto/subtle";
"hash"; big "gmp";
"io"; "hash";
"os"; "io";
"os";
) )
var bigOne = big.NewInt(1) var bigOne = big.NewInt(1)
@ -92,7 +93,7 @@ type PublicKey struct {
// A PrivateKey represents an RSA key // A PrivateKey represents an RSA key
type PrivateKey struct { type PrivateKey struct {
PublicKey; // public part. PublicKey; // public part.
D *big.Int; // private exponent D *big.Int; // private exponent
P, Q *big.Int; // prime factors of N P, Q *big.Int; // prime factors of N
} }
@ -300,58 +301,6 @@ func modInverse(a, n *big.Int) (ia *big.Int) {
return x; 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 // decrypt performs an RSA decryption, resulting in a plaintext integer. If a
// random source is given, RSA blinding is used. // 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(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.) // anything about this.)
em := leftPad(m.Bytes(), k); em := leftPad(m.Bytes(), k);
firstByteIsZero := constantTimeByteEq(em[0], 0); firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0);
seed := em[1 : hash.Size() + 1]; seed := em[1 : hash.Size() + 1];
db := em[hash.Size() + 1 : len(em)]; 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 // attacks like: J. Manger. A Chosen Ciphertext Attack on RSA Optimal
// Asymmetric Encryption Padding (OAEP) as Standardized in PKCS #1 // Asymmetric Encryption Padding (OAEP) as Standardized in PKCS #1
// v2.0. In J. Kilian, editor, Advances in Cryptology. // 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 // The remainder of the plaintext must be zero or more 0x00, followed
// by 0x01, followed by the message. // 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)]; rest := db[hash.Size() : len(db)];
for i := 0; i < len(rest); i++ { for i := 0; i < len(rest); i++ {
equals0 := constantTimeByteEq(rest[i], 0); equals0 := subtle.ConstantTimeByteEq(rest[i], 0);
equals1 := constantTimeByteEq(rest[i], 1); equals1 := subtle.ConstantTimeByteEq(rest[i], 1);
index = constantTimeSelect(lookingForIndex & equals1, i, index); index = subtle.ConstantTimeSelect(lookingForIndex & equals1, i, index);
lookingForIndex = constantTimeSelect(equals1, 0, lookingForIndex); lookingForIndex = subtle.ConstantTimeSelect(equals1, 0, lookingForIndex);
invalid = constantTimeSelect(lookingForIndex & ^equals0, 1, invalid); invalid = subtle.ConstantTimeSelect(lookingForIndex & ^equals0, 1, invalid);
} }
if firstByteIsZero & lHash2Good & ^invalid & ^lookingForIndex != 1 { if firstByteIsZero & lHash2Good & ^invalid & ^lookingForIndex != 1 {

189
src/pkg/crypto/rsa/rsa_test.go
View File

@ -5,12 +5,11 @@
package rsa package rsa
import ( import (
"bytes"; "bytes";
"crypto/sha1"; "crypto/sha1";
big "gmp"; big "gmp";
"os"; "os";
"testing"; "testing";
"testing/quick";
) )
func TestKeyGeneration(t *testing.T) { func TestKeyGeneration(t *testing.T) {
@ -109,101 +108,6 @@ func TestDecryptOAEP(t *testing.T) {
} }
} }
type TestConstantTimeCompareStruct struct {
a, b []byte;
out int;
}
var testConstandTimeCompareData = []TestConstantTimeCompareStruct{
TestConstantTimeCompareStruct{[]byte{}, []byte{}, 1},
TestConstantTimeCompareStruct{[]byte{0x11}, []byte{0x11}, 1},
TestConstantTimeCompareStruct{[]byte{0x12}, []byte{0x11}, 0},
}
func TestConstantTimeCompare(t *testing.T) {
for i, test := range testConstandTimeCompareData {
if r := constantTimeCompare(test.a, test.b); r != test.out {
t.Errorf("#%d bad result (got %x, want %x)", i, r, test.out);
}
}
}
type TestConstantTimeByteEqStruct struct {
a, b uint8;
out int;
}
var testConstandTimeByteEqData = []TestConstantTimeByteEqStruct{
TestConstantTimeByteEqStruct{0, 0, 1},
TestConstantTimeByteEqStruct{0, 1, 0},
TestConstantTimeByteEqStruct{1, 0, 0},
TestConstantTimeByteEqStruct{0xff, 0xff, 1},
TestConstantTimeByteEqStruct{0xff, 0xfe, 0},
}
func ByteEq(a, b uint8) int {
if a == b {
return 1;
}
return 0;
}
func TestConstantTimeByteEq(t *testing.T) {
for i, test := range testConstandTimeByteEqData {
if r := constantTimeByteEq(test.a, test.b); r != test.out {
t.Errorf("#%d bad result (got %x, want %x)", i, r, test.out);
}
}
err := quick.CheckEqual(constantTimeByteEq, ByteEq, nil);
if err != nil {
t.Error(err);
}
}
func Eq(a, b int32) int {
if a == b {
return 1;
}
return 0;
}
func TestConstantTimeEq(t *testing.T) {
err := quick.CheckEqual(constantTimeEq, Eq, nil);
if err != nil {
t.Error(err);
}
}
func Copy(v int, x, y []byte) []byte {
if len(x) > len(y) {
x = x[0:len(y)];
} else {
y = y[0:len(x)];
}
if v == 1 {
bytes.Copy(x, y);
}
return x;
}
func constantTimeCopyWrapper(v int, x, y []byte) []byte {
if len(x) > len(y) {
x = x[0:len(y)];
} else {
y = y[0:len(x)];
}
v &= 1;
constantTimeCopy(v, x, y);
return x;
}
func TestConstantTimeCopy(t *testing.T) {
err := quick.CheckEqual(constantTimeCopyWrapper, Copy, nil);
if err != nil {
t.Error(err);
}
}
// testEncryptOAEPData contains a subset of the vectors from RSA's "Test vectors for RSA-OAEP". // testEncryptOAEPData contains a subset of the vectors from RSA's "Test vectors for RSA-OAEP".
var testEncryptOAEPData = []testEncryptOAEPStruct{ var testEncryptOAEPData = []testEncryptOAEPStruct{
// Key 1 // Key 1
@ -305,47 +209,48 @@ var testEncryptOAEPData = []testEncryptOAEPStruct{
65537, 65537,
"056b04216fe5f354ac77250a4b6b0c8525a85c59b0bd80c56450a22d5f438e596a333aa875e291dd43f48cb88b9d5fc0d499f9fcd1c397f9afc070cd9e398c8d19e61db7c7410a6b2675dfbf5d345b804d201add502d5ce2dfcb091ce9997bbebe57306f383e4d588103f036f7e85d1934d152a323e4a8db451d6f4a5b1b0f102cc150e02feee2b88dea4ad4c1baccb24d84072d14e1d24a6771f7408ee30564fb86d4393a34bcf0b788501d193303f13a2284b001f0f649eaf79328d4ac5c430ab4414920a9460ed1b7bc40ec653e876d09abc509ae45b525190116a0c26101848298509c1c3bf3a483e7274054e15e97075036e989f60932807b5257751e79", "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",
[]testEncryptOAEPMessage{ []testEncryptOAEPMessage{
// Example 10.1 // Example 10.1
testEncryptOAEPMessage{ testEncryptOAEPMessage{
[]byte{0x8b, 0xba, 0x6b, 0xf8, 0x2a, 0x6c, 0x0f, 0x86, []byte{0x8b, 0xba, 0x6b, 0xf8, 0x2a, 0x6c, 0x0f, 0x86,
0xd5, 0xf1, 0x75, 0x6e, 0x97, 0x95, 0x68, 0x70, 0xb0, 0xd5, 0xf1, 0x75, 0x6e, 0x97, 0x95, 0x68, 0x70, 0xb0,
0x89, 0x53, 0xb0, 0x6b, 0x4e, 0xb2, 0x05, 0xbc, 0x16, 0x89, 0x53, 0xb0, 0x6b, 0x4e, 0xb2, 0x05, 0xbc, 0x16,
0x94, 0xee, 0x94, 0xee,
},
[]byte{0x47, 0xe1, 0xab, 0x71, 0x19, 0xfe, 0xe5, 0x6c,
0x95, 0xee, 0x5e, 0xaa, 0xd8, 0x6f, 0x40, 0xd0, 0xaa,
0x63, 0xbd, 0x33,
},
[]byte{0x53, 0xea, 0x5d, 0xc0, 0x8c, 0xd2, 0x60, 0xfb,
0x3b, 0x85, 0x85, 0x67, 0x28, 0x7f, 0xa9, 0x15, 0x52,
0xc3, 0x0b, 0x2f, 0xeb, 0xfb, 0xa2, 0x13, 0xf0, 0xae,
0x87, 0x70, 0x2d, 0x06, 0x8d, 0x19, 0xba, 0xb0, 0x7f,
0xe5, 0x74, 0x52, 0x3d, 0xfb, 0x42, 0x13, 0x9d, 0x68,
0xc3, 0xc5, 0xaf, 0xee, 0xe0, 0xbf, 0xe4, 0xcb, 0x79,
0x69, 0xcb, 0xf3, 0x82, 0xb8, 0x04, 0xd6, 0xe6, 0x13,
0x96, 0x14, 0x4e, 0x2d, 0x0e, 0x60, 0x74, 0x1f, 0x89,
0x93, 0xc3, 0x01, 0x4b, 0x58, 0xb9, 0xb1, 0x95, 0x7a,
0x8b, 0xab, 0xcd, 0x23, 0xaf, 0x85, 0x4f, 0x4c, 0x35,
0x6f, 0xb1, 0x66, 0x2a, 0xa7, 0x2b, 0xfc, 0xc7, 0xe5,
0x86, 0x55, 0x9d, 0xc4, 0x28, 0x0d, 0x16, 0x0c, 0x12,
0x67, 0x85, 0xa7, 0x23, 0xeb, 0xee, 0xbe, 0xff, 0x71,
0xf1, 0x15, 0x94, 0x44, 0x0a, 0xae, 0xf8, 0x7d, 0x10,
0x79, 0x3a, 0x87, 0x74, 0xa2, 0x39, 0xd4, 0xa0, 0x4c,
0x87, 0xfe, 0x14, 0x67, 0xb9, 0xda, 0xf8, 0x52, 0x08,
0xec, 0x6c, 0x72, 0x55, 0x79, 0x4a, 0x96, 0xcc, 0x29,
0x14, 0x2f, 0x9a, 0x8b, 0xd4, 0x18, 0xe3, 0xc1, 0xfd,
0x67, 0x34, 0x4b, 0x0c, 0xd0, 0x82, 0x9d, 0xf3, 0xb2,
0xbe, 0xc6, 0x02, 0x53, 0x19, 0x62, 0x93, 0xc6, 0xb3,
0x4d, 0x3f, 0x75, 0xd3, 0x2f, 0x21, 0x3d, 0xd4, 0x5c,
0x62, 0x73, 0xd5, 0x05, 0xad, 0xf4, 0xcc, 0xed, 0x10,
0x57, 0xcb, 0x75, 0x8f, 0xc2, 0x6a, 0xee, 0xfa, 0x44,
0x12, 0x55, 0xed, 0x4e, 0x64, 0xc1, 0x99, 0xee, 0x07,
0x5e, 0x7f, 0x16, 0x64, 0x61, 0x82, 0xfd, 0xb4, 0x64,
0x73, 0x9b, 0x68, 0xab, 0x5d, 0xaf, 0xf0, 0xe6, 0x3e,
0x95, 0x52, 0x01, 0x68, 0x24, 0xf0, 0x54, 0xbf, 0x4d,
0x3c, 0x8c, 0x90, 0xa9, 0x7b, 0xb6, 0xb6, 0x55, 0x32,
0x84, 0xeb, 0x42, 0x9f, 0xcc,
},
}, },
[]byte{0x47, 0xe1, 0xab, 0x71, 0x19, 0xfe, 0xe5, 0x6c, },
0x95, 0xee, 0x5e, 0xaa, 0xd8, 0x6f, 0x40, 0xd0, 0xaa,
0x63, 0xbd, 0x33,
},
[]byte{0x53, 0xea, 0x5d, 0xc0, 0x8c, 0xd2, 0x60, 0xfb,
0x3b, 0x85, 0x85, 0x67, 0x28, 0x7f, 0xa9, 0x15, 0x52,
0xc3, 0x0b, 0x2f, 0xeb, 0xfb, 0xa2, 0x13, 0xf0, 0xae,
0x87, 0x70, 0x2d, 0x06, 0x8d, 0x19, 0xba, 0xb0, 0x7f,
0xe5, 0x74, 0x52, 0x3d, 0xfb, 0x42, 0x13, 0x9d, 0x68,
0xc3, 0xc5, 0xaf, 0xee, 0xe0, 0xbf, 0xe4, 0xcb, 0x79,
0x69, 0xcb, 0xf3, 0x82, 0xb8, 0x04, 0xd6, 0xe6, 0x13,
0x96, 0x14, 0x4e, 0x2d, 0x0e, 0x60, 0x74, 0x1f, 0x89,
0x93, 0xc3, 0x01, 0x4b, 0x58, 0xb9, 0xb1, 0x95, 0x7a,
0x8b, 0xab, 0xcd, 0x23, 0xaf, 0x85, 0x4f, 0x4c, 0x35,
0x6f, 0xb1, 0x66, 0x2a, 0xa7, 0x2b, 0xfc, 0xc7, 0xe5,
0x86, 0x55, 0x9d, 0xc4, 0x28, 0x0d, 0x16, 0x0c, 0x12,
0x67, 0x85, 0xa7, 0x23, 0xeb, 0xee, 0xbe, 0xff, 0x71,
0xf1, 0x15, 0x94, 0x44, 0x0a, 0xae, 0xf8, 0x7d, 0x10,
0x79, 0x3a, 0x87, 0x74, 0xa2, 0x39, 0xd4, 0xa0, 0x4c,
0x87, 0xfe, 0x14, 0x67, 0xb9, 0xda, 0xf8, 0x52, 0x08,
0xec, 0x6c, 0x72, 0x55, 0x79, 0x4a, 0x96, 0xcc, 0x29,
0x14, 0x2f, 0x9a, 0x8b, 0xd4, 0x18, 0xe3, 0xc1, 0xfd,
0x67, 0x34, 0x4b, 0x0c, 0xd0, 0x82, 0x9d, 0xf3, 0xb2,
0xbe, 0xc6, 0x02, 0x53, 0x19, 0x62, 0x93, 0xc6, 0xb3,
0x4d, 0x3f, 0x75, 0xd3, 0x2f, 0x21, 0x3d, 0xd4, 0x5c,
0x62, 0x73, 0xd5, 0x05, 0xad, 0xf4, 0xcc, 0xed, 0x10,
0x57, 0xcb, 0x75, 0x8f, 0xc2, 0x6a, 0xee, 0xfa, 0x44,
0x12, 0x55, 0xed, 0x4e, 0x64, 0xc1, 0x99, 0xee, 0x07,
0x5e, 0x7f, 0x16, 0x64, 0x61, 0x82, 0xfd, 0xb4, 0x64,
0x73, 0x9b, 0x68, 0xab, 0x5d, 0xaf, 0xf0, 0xe6, 0x3e,
0x95, 0x52, 0x01, 0x68, 0x24, 0xf0, 0x54, 0xbf, 0x4d,
0x3c, 0x8c, 0x90, 0xa9, 0x7b, 0xb6, 0xb6, 0x55, 0x32,
0x84, 0xeb, 0x42, 0x9f, 0xcc,
},
}},
}, },
} }

11
src/pkg/crypto/subtle/Makefile Normal file
View File

@ -0,0 +1,11 @@
# 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.
include $(GOROOT)/src/Make.$(GOARCH)
TARG=crypto/subtle
GOFILES=\
constant_time.go\
include $(GOROOT)/src/Make.pkg

59
src/pkg/crypto/subtle/constant_time.go Normal file
View File

@ -0,0 +1,59 @@
// 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.
// This package implements functions that are often useful in cryptographic
// code but require careful thought to use correctly.
package subtle
// 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 x if v is 1 and y if v is 0.
// Its behavior is undefined if v takes any other value.
func ConstantTimeSelect(v, x, y int) int {
return ^(v-1) & x | (v-1)&y;
}
// ConstantTimeByteEq returns 1 if x == x and 0 otherwise.
func ConstantTimeByteEq(x, y uint8) int {
z := ^(x^y);
z &= z>>4;
z &= z>>2;
z &= z>>1;
return int(z);
}
// ConstantTimeEq returns 1 if x == y and 0 otherwise.
func ConstantTimeEq(x, y int32) int {
z := ^(x^y);
z &= z>>16;
z &= z>>8;
z &= z>>4;
z &= z>>2;
z &= z>>1;
return int(z&1);
}
// ConstantTimeCopy copies the contents of y into x iff v == 1. If v == 0, x is left unchanged.
// Its behavior 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;
}

106
src/pkg/crypto/subtle/constant_time_test.go Normal file
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// 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 subtle
import (
"bytes";
"testing";
"testing/quick";
)
type TestConstantTimeCompareStruct struct {
a, b []byte;
out int;
}
var testConstandTimeCompareData = []TestConstantTimeCompareStruct{
TestConstantTimeCompareStruct{[]byte{}, []byte{}, 1},
TestConstantTimeCompareStruct{[]byte{0x11}, []byte{0x11}, 1},
TestConstantTimeCompareStruct{[]byte{0x12}, []byte{0x11}, 0},
}
func TestConstantTimeCompare(t *testing.T) {
for i, test := range testConstandTimeCompareData {
if r := ConstantTimeCompare(test.a, test.b); r != test.out {
t.Errorf("#%d bad result (got %x, want %x)", i, r, test.out);
}
}
}
type TestConstantTimeByteEqStruct struct {
a, b uint8;
out int;
}
var testConstandTimeByteEqData = []TestConstantTimeByteEqStruct{
TestConstantTimeByteEqStruct{0, 0, 1},
TestConstantTimeByteEqStruct{0, 1, 0},
TestConstantTimeByteEqStruct{1, 0, 0},
TestConstantTimeByteEqStruct{0xff, 0xff, 1},
TestConstantTimeByteEqStruct{0xff, 0xfe, 0},
}
func byteEq(a, b uint8) int {
if a == b {
return 1;
}
return 0;
}
func TestConstantTimeByteEq(t *testing.T) {
for i, test := range testConstandTimeByteEqData {
if r := ConstantTimeByteEq(test.a, test.b); r != test.out {
t.Errorf("#%d bad result (got %x, want %x)", i, r, test.out);
}
}
err := quick.CheckEqual(ConstantTimeByteEq, byteEq, nil);
if err != nil {
t.Error(err);
}
}
func eq(a, b int32) int {
if a == b {
return 1;
}
return 0;
}
func TestConstantTimeEq(t *testing.T) {
err := quick.CheckEqual(ConstantTimeEq, eq, nil);
if err != nil {
t.Error(err);
}
}
func copy(v int, x, y []byte) []byte {
if len(x) > len(y) {
x = x[0:len(y)];
} else {
y = y[0:len(x)];
}
if v == 1 {
bytes.Copy(x, y);
}
return x;
}
func constantTimeCopyWrapper(v int, x, y []byte) []byte {
if len(x) > len(y) {
x = x[0:len(y)];
} else {
y = y[0:len(x)];
}
v &= 1;
ConstantTimeCopy(v, x, y);
return x;
}
func TestConstantTimeCopy(t *testing.T) {
err := quick.CheckEqual(constantTimeCopyWrapper, copy, nil);
if err != nil {
t.Error(err);
}
}