static int bn_cmp_words_consttime(const BN_ULONG *a, size_t a_len,
const BN_ULONG *b, size_t b_len) {
OPENSSL_COMPILE_ASSERT(sizeof(BN_ULONG) <= sizeof(crypto_word_t),
crypto_word_t_too_small);
int ret = 0;
// Process the common words in little-endian order.
size_t min = a_len < b_len ? a_len : b_len;
for (size_t i = 0; i < min; i++) {
crypto_word_t eq = constant_time_eq_w(a[i], b[i]);
crypto_word_t lt = constant_time_lt_w(a[i], b[i]);
ret =
constant_time_select_int(eq, ret, constant_time_select_int(lt, -1, 1));
}
// If |a| or |b| has non-zero words beyond |min|, they take precedence.
if (a_len < b_len) {
crypto_word_t mask = 0;
for (size_t i = a_len; i < b_len; i++) {
mask |= b[i];
}
ret = constant_time_select_int(constant_time_is_zero_w(mask), ret, -1);
} else if (b_len < a_len) {
crypto_word_t mask = 0;
for (size_t i = b_len; i < a_len; i++) {
mask |= a[i];
}
ret = constant_time_select_int(constant_time_is_zero_w(mask), ret, 1);
}
return ret;
}
static void ec_GFp_simple_mul_single(const EC_GROUP *group, EC_RAW_POINT *r,
const EC_RAW_POINT *p,
const EC_SCALAR *scalar) {
// This is a generic implementation for uncommon curves that not do not
// warrant a tuned one. It uses unsigned digits so that the doubling case in
// |ec_GFp_simple_add| is always unreachable, erring on safety and simplicity.
// Compute a table of the first 32 multiples of |p| (including infinity).
EC_RAW_POINT precomp[32];
ec_GFp_simple_point_set_to_infinity(group, &precomp[0]);
ec_GFp_simple_point_copy(&precomp[1], p);
for (size_t j = 2; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
if (j & 1) {
ec_GFp_simple_add(group, &precomp[j], &precomp[1], &precomp[j - 1]);
} else {
ec_GFp_simple_dbl(group, &precomp[j], &precomp[j / 2]);
}
}
// Divide bits in |scalar| into windows.
unsigned bits = BN_num_bits(&group->order);
int r_is_at_infinity = 1;
for (unsigned i = bits - 1; i < bits; i--) {
if (!r_is_at_infinity) {
ec_GFp_simple_dbl(group, r, r);
}
if (i % 5 == 0) {
// Compute the next window value.
const size_t width = group->order.width;
uint8_t window = bn_is_bit_set_words(scalar->words, width, i + 4) << 4;
window |= bn_is_bit_set_words(scalar->words, width, i + 3) << 3;
window |= bn_is_bit_set_words(scalar->words, width, i + 2) << 2;
window |= bn_is_bit_set_words(scalar->words, width, i + 1) << 1;
window |= bn_is_bit_set_words(scalar->words, width, i);
// Select the entry in constant-time.
EC_RAW_POINT tmp;
OPENSSL_memset(&tmp, 0, sizeof(EC_RAW_POINT));
for (size_t j = 0; j < OPENSSL_ARRAY_SIZE(precomp); j++) {
BN_ULONG mask = constant_time_eq_w(j, window);
ec_felem_select(group, &tmp.X, mask, &precomp[j].X, &tmp.X);
ec_felem_select(group, &tmp.Y, mask, &precomp[j].Y, &tmp.Y);
ec_felem_select(group, &tmp.Z, mask, &precomp[j].Z, &tmp.Z);
}
if (r_is_at_infinity) {
ec_GFp_simple_point_copy(r, &tmp);
r_is_at_infinity = 0;
} else {
ec_GFp_simple_add(group, r, r, &tmp);
}
}
}
if (r_is_at_infinity) {
ec_GFp_simple_point_set_to_infinity(group, r);
}
}
/* reverse_and_mulX_ghash interprets the bytes |b->c| as a reversed element of
* the GHASH field, multiplies that by 'x' and serialises the result back into
* |b|, but with GHASH's backwards bit ordering. */
static void reverse_and_mulX_ghash(polyval_block *b) {
uint64_t hi = b->u[0];
uint64_t lo = b->u[1];
const crypto_word_t carry = constant_time_eq_w(hi & 1, 1);
hi >>= 1;
hi |= lo << 63;
lo >>= 1;
lo ^= ((uint64_t) constant_time_select_w(carry, 0xe1, 0)) << 56;
b->u[0] = CRYPTO_bswap8(lo);
b->u[1] = CRYPTO_bswap8(hi);
}
int EVP_tls_cbc_remove_padding(crypto_word_t *out_padding_ok, size_t *out_len,
const uint8_t *in, size_t in_len,
size_t block_size, size_t mac_size) {
const size_t overhead = 1 /* padding length byte */ + mac_size;
/* These lengths are all public so we can test them in non-constant time. */
if (overhead > in_len) {
return 0;
}
size_t padding_length = in[in_len - 1];
crypto_word_t good = constant_time_ge_w(in_len, overhead + padding_length);
/* The padding consists of a length byte at the end of the record and
* then that many bytes of padding, all with the same value as the
* length byte. Thus, with the length byte included, there are i+1
* bytes of padding.
*
* We can't check just |padding_length+1| bytes because that leaks
* decrypted information. Therefore we always have to check the maximum
* amount of padding possible. (Again, the length of the record is
* public information so we can use it.) */
size_t to_check = 256; /* maximum amount of padding, inc length byte. */
if (to_check > in_len) {
to_check = in_len;
}
for (size_t i = 0; i < to_check; i++) {
uint8_t mask = constant_time_ge_8(padding_length, i);
uint8_t b = in[in_len - 1 - i];
/* The final |padding_length+1| bytes should all have the value
* |padding_length|. Therefore the XOR should be zero. */
good &= ~(mask & (padding_length ^ b));
}
/* If any of the final |padding_length+1| bytes had the wrong value,
* one or more of the lower eight bits of |good| will be cleared. */
good = constant_time_eq_w(0xff, good & 0xff);
/* Always treat |padding_length| as zero on error. If, assuming block size of
* 16, a padding of [<15 arbitrary bytes> 15] treated |padding_length| as 16
* and returned -1, distinguishing good MAC and bad padding from bad MAC and
* bad padding would give POODLE's padding oracle. */
padding_length = good & (padding_length + 1);
*out_len = in_len - padding_length;
*out_padding_ok = good;
return 1;
}
void EVP_tls_cbc_copy_mac(uint8_t *out, size_t md_size, const uint8_t *in,
size_t in_len, size_t orig_len) {
uint8_t rotated_mac1[EVP_MAX_MD_SIZE], rotated_mac2[EVP_MAX_MD_SIZE];
uint8_t *rotated_mac = rotated_mac1;
uint8_t *rotated_mac_tmp = rotated_mac2;
/* mac_end is the index of |in| just after the end of the MAC. */
size_t mac_end = in_len;
size_t mac_start = mac_end - md_size;
assert(orig_len >= in_len);
assert(in_len >= md_size);
assert(md_size <= EVP_MAX_MD_SIZE);
/* scan_start contains the number of bytes that we can ignore because
* the MAC's position can only vary by 255 bytes. */
size_t scan_start = 0;
/* This information is public so it's safe to branch based on it. */
if (orig_len > md_size + 255 + 1) {
scan_start = orig_len - (md_size + 255 + 1);
}
size_t rotate_offset = 0;
uint8_t mac_started = 0;
OPENSSL_memset(rotated_mac, 0, md_size);
for (size_t i = scan_start, j = 0; i < orig_len; i++, j++) {
if (j >= md_size) {
j -= md_size;
}
crypto_word_t is_mac_start = constant_time_eq_w(i, mac_start);
mac_started |= is_mac_start;
uint8_t mac_ended = constant_time_ge_8(i, mac_end);
rotated_mac[j] |= in[i] & mac_started & ~mac_ended;
/* Save the offset that |mac_start| is mapped to. */
rotate_offset |= j & is_mac_start;
}
/* Now rotate the MAC. We rotate in log(md_size) steps, one for each bit
* position. */
for (size_t offset = 1; offset < md_size; offset <<= 1, rotate_offset >>= 1) {
/* Rotate by |offset| iff the corresponding bit is set in
* |rotate_offset|, placing the result in |rotated_mac_tmp|. */
const uint8_t skip_rotate = (rotate_offset & 1) - 1;
for (size_t i = 0, j = offset; i < md_size; i++, j++) {
if (j >= md_size) {
j -= md_size;
}
rotated_mac_tmp[i] =
constant_time_select_8(skip_rotate, rotated_mac[i], rotated_mac[j]);
}
/* Swap pointers so |rotated_mac| contains the (possibly) rotated value.
* Note the number of iterations and thus the identity of these pointers is
* public information. */
uint8_t *tmp = rotated_mac;
rotated_mac = rotated_mac_tmp;
rotated_mac_tmp = tmp;
}
OPENSSL_memcpy(out, rotated_mac, md_size);
}
