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Add another option to reduce EC memory usage

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Also document speed/memory trade-offs better.
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Manuel Pégourié-Gonnard 2013-12-30 18:41:16 +01:00
parent 70896a023e
commit 9e4191c3e7
3 changed files with 31 additions and 3 deletions
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26
include/polarssl/ecp.h
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@ -178,11 +178,33 @@ ecp_keypair;
* Minimum value: 2. Maximum value: 7.
*
* Result is an array of at most ( 1 << ( POLARSSL_ECP_WINDOW_SIZE - 1 ) )
* points used for point multiplication.
* points used for point multiplication. This value is directly tied to EC
* peak memory usage, so decreasing it by one should roughly cut memory usage
* by two (if large curves are in use).
*
* Reduction in size may reduce speed for big curves.
* Reduction in size may reduce speed, but larger curves are impacted first.
* Sample performances (in ECDHE handshakes/s, with FIXED_POINT_OPTIM = 1):
* w-size: 6 5 4 3 2
* 521 145 141 135 120 97
* 384 214 209 198 177 146
* 256 320 320 303 262 226
* 224 475 475 453 398 342
* 192 640 640 633 587 476
*/
#define POLARSSL_ECP_WINDOW_SIZE 6 /**< Maximum window size used */
/*
* Trade memory for speed on fixed-point multiplication.
*
* This speeds up repeated multiplication of the generator (that is, the
* multiplication in ECDSA signatures, and half of the multiplications in
* ECDSA verification and ECDHE) by a factor roughly 3 to 4.
*
* The cost is increasing EC peak memory usage by a factor roughly 2.
*
* Change this value to 0 to reduce peak memory usage.
*/
#define POLARSSL_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up */
#endif
/*