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Determine MBEDTLS_ECP_MAX_BITS automatically

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MBEDTLS_ECP_MAX_BITS doesn't make sense as a configuration option: it
must not be smaller than the largest supported curve, and it's useless
to set it to a larger value. So unconditionally set it to the size of
the largest supported curve. Remove it from the build configuration.

Alternative implementations must no longer need define this macro.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-05-28 00:17:26 +02:00
parent 9ef1ea7444
commit d0b16303bb
4 changed files with 40 additions and 12 deletions
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3
configs/config-suite-b.h
View file

@ -84,8 +84,7 @@
#define MBEDTLS_AES_ROM_TABLES
/* Save RAM by adjusting to our exact needs */
#define MBEDTLS_ECP_MAX_BITS 384
#define MBEDTLS_MPI_MAX_SIZE 48 // 384 bits is 48 bytes
#define MBEDTLS_MPI_MAX_SIZE 48 // 384-bit EC curve = 48 bytes
/* Save RAM at the expense of speed, see ecp.h */
#define MBEDTLS_ECP_WINDOW_SIZE 2

3
configs/config-thread.h
View file

@ -85,8 +85,7 @@
#define MBEDTLS_AES_ROM_TABLES
/* Save RAM by adjusting to our exact needs */
#define MBEDTLS_ECP_MAX_BITS 256
#define MBEDTLS_MPI_MAX_SIZE 32 // 256 bits is 32 bytes
#define MBEDTLS_MPI_MAX_SIZE 32 // 256-bit EC curve = 32 bytes
/* Save ROM and a few bytes of RAM by specifying our own ciphersuite list */
#define MBEDTLS_SSL_CIPHERSUITES MBEDTLS_TLS_ECJPAKE_WITH_AES_128_CCM_8

1
include/mbedtls/config.h
View file

@ -3155,7 +3155,6 @@
//#define MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT 384 /**< Maximum size of (re)seed buffer */
/* ECP options */
//#define MBEDTLS_ECP_MAX_BITS 521 /**< Maximum bit size of groups */
//#define MBEDTLS_ECP_WINDOW_SIZE 6 /**< Maximum window size used */
//#define MBEDTLS_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up */

45
include/mbedtls/ecp.h
View file

@ -242,13 +242,6 @@ mbedtls_ecp_group;
* \{
*/
#if !defined(MBEDTLS_ECP_MAX_BITS)
/**
* The maximum size of the groups, that is, of \c N and \c P.
*/
#define MBEDTLS_ECP_MAX_BITS 521 /**< The maximum size of groups, in bits. */
#endif
#if !defined(MBEDTLS_ECP_WINDOW_SIZE)
/*
* Maximum "window" size used for point multiplication.
@ -294,6 +287,44 @@ mbedtls_ecp_group;
#include "ecp_alt.h"
#endif /* MBEDTLS_ECP_ALT */
/**
* The maximum size of the groups, that is, of \c N and \c P.
*/
#if !defined(MBEDTLS_ECP_C)
/* Dummy definition to help code that has optional ECP support and
* defines an MBEDTLS_ECP_MAX_BYTES-sized array unconditionally. */
#define MBEDTLS_ECP_MAX_BITS 1
/* Note: the curves must be listed in DECREASING size! */
#elif defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 521
#elif defined(MBEDTLS_ECP_DP_BP512R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 512
#elif defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 448
#elif defined(MBEDTLS_ECP_DP_BP384R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 384
#elif defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 384
#elif defined(MBEDTLS_ECP_DP_BP256R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 256
#elif defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 256
#elif defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 256
#elif defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 255
#elif defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 225 // n is slightly above 2^224
#elif defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 224
#elif defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 192
#elif defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED)
#define MBEDTLS_ECP_MAX_BITS 192
#else
#error "Missing definition of MBEDTLS_ECP_MAX_BITS"
#endif
#define MBEDTLS_ECP_MAX_BYTES ( ( MBEDTLS_ECP_MAX_BITS + 7 ) / 8 )
#define MBEDTLS_ECP_MAX_PT_LEN ( 2 * MBEDTLS_ECP_MAX_BYTES + 1 )