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feat(crypto): introduce bn_read_be_512

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This commit is contained in:
Ondřej Vejpustek 2023-09-19 15:01:30 +02:00
parent 93bb4c2e35
commit 4a686d9231
3 changed files with 36 additions and 0 deletions
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24
crypto/bignum.c
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@ -107,6 +107,30 @@ void bn_read_be(const uint8_t *in_number, bignum256 *out_number) {
out_number->val[BN_LIMBS - 1] = temp;
}
// out_number = (bignum512) in_number
// Assumes in_number is a raw bigendian 512-bit number
// Guarantees out_number is normalized
void bn_read_be_512(const uint8_t *in_number, bignum512 *out_number) {
bignum256 lower = {0}, upper = {0};
bn_read_be(in_number + 32, &lower);
bn_read_be(in_number, &upper);
const int shift_length = BN_BITS_PER_LIMB * BN_LIMBS - 256;
uint32_t shift = upper.val[0] & ((1 << shift_length) - 1);
for (int i = 0; i < shift_length; i++) {
bn_rshift(&upper);
}
lower.val[BN_LIMBS - 1] |= shift << (BN_BITS_PER_LIMB - shift_length);
for (int i = 0; i < BN_LIMBS; i++) {
out_number->val[i] = lower.val[i];
}
for (int i = 0; i < BN_LIMBS; i++) {
out_number->val[i + BN_LIMBS] = upper.val[i];
}
}
// out_number = (256BE) in_number
// Assumes in_number < 2**256
// Guarantess out_number is a raw bigendian 256-bit number

1
crypto/bignum.h
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@ -74,6 +74,7 @@ static inline void write_le(uint8_t *data, uint32_t x) {
void bn_copy_lower(const bignum512 *x, bignum256 *y);
void bn_read_be(const uint8_t *in_number, bignum256 *out_number);
void bn_read_be_512(const uint8_t *in_number, bignum512 *out_number);
void bn_write_be(const bignum256 *in_number, uint8_t *out_number);
void bn_read_le(const uint8_t *in_number, bignum256 *out_number);
void bn_write_le(const bignum256 *in_number, uint8_t *out_number);

11
crypto/tests/test_bignum.py
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@ -216,6 +216,13 @@ def assert_bn_read_be(in_number):
assert bignum_is_normalised(bn_out_number)
assert out_number == in_number
def assert_bn_read_be_512(in_number):
raw_in_number = integer_to_raw_number512(in_number, "big")
bn_out_number = bignum512()
lib.bn_read_be_512(raw_in_number, bn_out_number)
out_number = bignum512_to_int(bn_out_number)
assert bignum_is_normalised(bn_out_number)
assert out_number == in_number
@ -760,6 +767,10 @@ def test_bn_read_be(r):
assert_bn_read_be(r.rand_int_256())
def test_bn_read_be_512(r):
assert_bn_read_be_512(r.rand_int_512())
def test_bn_read_le(r):
assert_bn_read_le(r.rand_int_256())