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Avoid superflous randomization with restartable

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Checking the budget only after the randomization is done means sometimes we
were randomizing first, then noticing we ran out of budget, return, come back
and randomize again before we finally normalize.

While this is fine from a correctness and security perspective, it's a minor
inefficiency, and can also be disconcerting while debugging, so we might as
well avoid it.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard 2020-06-08 09:53:20 +02:00
parent c7295f5416
commit 18b0b3c4b5
1 changed files with 1 additions and 1 deletions
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2
library/ecp.c
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@ -2073,6 +2073,7 @@ static int ecp_mul_comb_after_precomp( const mbedtls_ecp_group *grp,
rs_ctx->rsm->state = ecp_rsm_final_norm; rs_ctx->rsm->state = ecp_rsm_final_norm;
final_norm: final_norm:
MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV );
#endif #endif
/* /*
* Knowledge of the jacobian coordinates may leak the last few bits of the * Knowledge of the jacobian coordinates may leak the last few bits of the
@ -2090,7 +2091,6 @@ final_norm:
#endif #endif
MBEDTLS_MPI_CHK( ecp_randomize_jac( grp, RR, f_rng, p_rng ) ); MBEDTLS_MPI_CHK( ecp_randomize_jac( grp, RR, f_rng, p_rng ) );
MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV );
MBEDTLS_MPI_CHK( ecp_normalize_jac( grp, RR ) ); MBEDTLS_MPI_CHK( ecp_normalize_jac( grp, RR ) );
#if defined(MBEDTLS_ECP_RESTARTABLE) #if defined(MBEDTLS_ECP_RESTARTABLE)