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adjusting size of sliding window array to correct size. #3592

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merged 4 commits into from
Sep 9, 2020
Merged

adjusting size of sliding window array to correct size. #3592

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388f9b2
adjusting size of sliding window array to correct size.
d-otte Aug 21, 2020
4374dc4
fixing spelling mistakes (window <-- windows)
d-otte Sep 7, 2020
6086151
adjusting comment on sliding window memory usage.
d-otte Sep 7, 2020
b9da1dd
adding entry file to ChangeLog.d for PR3592
d-otte Sep 7, 2020
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3 changes: 3 additions & 0 deletions ChangeLog.d/adjusting sliding_window_size_PR3592.txt
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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 changes: 2 additions & 2 deletions include/mbedtls/bignum.h
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Expand Up @@ -61,12 +61,12 @@
* 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)
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2 changes: 1 addition & 1 deletion include/mbedtls/config.h
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Expand Up @@ -3414,7 +3414,7 @@
*/

/* 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 */
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2 changes: 1 addition & 1 deletion library/bignum.c
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Expand Up @@ -2101,7 +2101,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
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;

MPI_VALIDATE_RET( X != NULL );
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