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Merge pull request #3652 from d-otte/mbedtls-2.7

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Backport 2.7: adjusting size of sliding window array to correct size
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Manuel Pégourié-Gonnard 2020-09-09 10:00:01 +02:00 committed by GitHub
parent 75ffb27577 72a410dcfc
commit 5796dfe197
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4 changed files with 7 additions and 4 deletions
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3
ChangeLog.d/adjusting sliding_window_size_PR3592.txt Normal file
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@ -0,0 +1,3 @@
Changes
* Reduce stack usage significantly during sliding window exponentiation.
Reported in #3591 and fix contributed in #3592 by Daniel Otte.

4
include/mbedtls/bignum.h
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@ -83,12 +83,12 @@
* Maximum window size used for modular exponentiation. Default: 6
* Minimum value: 1. Maximum value: 6.
*
* Result is an array of ( 2 << MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
* Result is an array of ( 2 ** MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
* for the sliding window calculation. (So 64 by default)
*
* Reduction in size, reduces speed.
*/
#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum windows size used. */
#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum window size used. */
#endif /* !MBEDTLS_MPI_WINDOW_SIZE */
#if !defined(MBEDTLS_MPI_MAX_SIZE)

2
include/mbedtls/config.h
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@ -2814,7 +2814,7 @@
*/
/* MPI / BIGNUM options */
//#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum windows size used. */
//#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum window size used. */
//#define MBEDTLS_MPI_MAX_SIZE 1024 /**< Maximum number of bytes for usable MPIs. */
/* CTR_DRBG options */

2
library/bignum.c
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@ -1850,7 +1850,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
size_t i, j, nblimbs;
size_t bufsize, nbits;
mbedtls_mpi_uint ei, mm, state;
mbedtls_mpi RR, T, W[ 2 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
mbedtls_mpi RR, T, W[ 1 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
int neg;
if( mbedtls_mpi_cmp_int( N, 0 ) <= 0 || ( N->p[0] & 1 ) == 0 )