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Update mpi_gcd_invmod_odd() related comments/documentation

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Signed-off-by: Felix Conway <felix.conway@arm.com>
This commit is contained in:
Felix Conway
2025-08-05 14:33:32 +01:00
parent f4df43b6c4
commit d9c4c9c441
3 changed files with 11 additions and 17 deletions
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2
library/bignum.c
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@@ -1764,7 +1764,7 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
}
/* Check aliasing requirements */
if (A == N || G == I || (I != NULL && (I == N || G == N))) {
if (A == N || (I != NULL && (I == N || G == N))) {
return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
}

12
library/bignum_internal.h
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@@ -48,14 +48,14 @@ int mbedtls_mpi_exp_mod_unsafe(mbedtls_mpi *X, const mbedtls_mpi *A,
mbedtls_mpi *prec_RR);
/**
* \brief Compute GCD(A, N) and/or A^-1 mod N if it exists,
* in constant time.
* \brief A wrapper around a constant time function to compute
* GCD(A, N) and/or A^-1 mod N if it exists.
*
* \warning Requires N to be odd, and 0 <= A <= N, and N > 1 if
* I != NULL.
* \warning Requires N to be odd, and 0 <= A <= N. Additionally, if
* I != NULL, requires N > 1.
* The wrapper part of this function is not constant time.
*
* \note G and I must not alias each other.
* A and N must not alias each other.
* \note A and N must not alias each other.
* When I == NULL (computing only the GCD), G can alias A or N.
* When I != NULL (computing the modular inverse), G or I can
* alias A, but neither of them can alias N (the modulus).

14
tests/suites/test_suite_bignum.function
View File

@@ -1162,6 +1162,8 @@ void mpi_gcd_modinv_odd_both(char *input_A, char *input_N,
TEST_EQUAL(mbedtls_test_read_mpi(&A, input_A), 0);
TEST_EQUAL(mbedtls_test_read_mpi(&N, input_N), 0);
TEST_EQUAL(mbedtls_test_read_mpi(&exp_G, result_G), 0);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (has_inverse) {
TEST_EQUAL(mbedtls_test_read_mpi(&exp_I, result_I), 0);
}
@@ -1171,8 +1173,6 @@ void mpi_gcd_modinv_odd_both(char *input_A, char *input_N,
if (res == 0) {
TEST_ASSERT(sign_is_valid(&G));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&G, &exp_G), 0);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (has_inverse) {
TEST_ASSERT(sign_is_valid(&I));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&I, &exp_I), 0);
@@ -1186,8 +1186,6 @@ void mpi_gcd_modinv_odd_both(char *input_A, char *input_N,
if (res == 0) {
TEST_ASSERT(sign_is_valid(&G));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&G, &exp_G), 0);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (has_inverse) {
TEST_ASSERT(sign_is_valid(&I));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&I, &exp_I), 0);
@@ -1206,8 +1204,6 @@ void mpi_gcd_modinv_odd_both(char *input_A, char *input_N,
if (res == 0) {
TEST_ASSERT(sign_is_valid(&G));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&G, &exp_G), 0);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (has_inverse) {
TEST_ASSERT(sign_is_valid(&I));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&I, &exp_I), 0);
@@ -1287,14 +1283,14 @@ void mpi_gcd_modinv_odd_only_modinv(char *input_A, char *input_N,
mbedtls_mpi_init(&exp_I);
TEST_EQUAL(mbedtls_test_read_mpi(&A, input_A), 0);
TEST_EQUAL(mbedtls_test_read_mpi(&N, input_N), 0);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (has_inverse) {
TEST_EQUAL(mbedtls_test_read_mpi(&exp_I, result_I), 0);
}
res = mbedtls_mpi_gcd_modinv_odd(NULL, &I, &A, &N);
TEST_EQUAL(res, return_code);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (res == 0 && has_inverse) {
TEST_ASSERT(sign_is_valid(&I));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&I, &exp_I), 0);
@@ -1304,8 +1300,6 @@ void mpi_gcd_modinv_odd_only_modinv(char *input_A, char *input_N,
TEST_EQUAL(mbedtls_test_read_mpi(&I, input_A), 0);
res = mbedtls_mpi_gcd_modinv_odd(NULL, &I, /* A */ &I, &N);
TEST_EQUAL(res, return_code);
/* If there is no inverse then the value returned in I will be
* indeterminate, and so not useful or possible to test. */
if (res == 0 && has_inverse) {
TEST_ASSERT(sign_is_valid(&I));
TEST_EQUAL(mbedtls_mpi_cmp_mpi(&I, &exp_I), 0);