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Exp mod: clarify preprocessing

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Signed-off-by: Janos Follath <janos.follath@arm.com>
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Janos Follath 2024-02-19 11:27:38 +00:00
parent 583f047c9f
commit 467a5499a5
1 changed files with 8 additions and 1 deletions
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9
library/bignum.c
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@ -1654,7 +1654,14 @@ int mbedtls_mpi_exp_mod(mbedtls_mpi *X, const mbedtls_mpi *A,
X->s = 1; X->s = 1;
/* /*
* Make sure that A has exactly as many limbs as N. * Make sure that X is in a form that is safe for consumption by
* the core functions.
*
* - The core functions will not touch the limbs of X above N->n. The
* result will be correct if those limbs are 0, which the mod call
* ensures.
* - Also, X must have at least as many limbs as N for the calls to the
* core functions.
*/ */
if (mbedtls_mpi_cmp_mpi(X, N) >= 0) { if (mbedtls_mpi_cmp_mpi(X, N) >= 0) {
MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(X, X, N)); MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(X, X, N));