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DHM: add notes about leading zeros

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-04-13 22:10:24 +02:00
parent ebe9b6a51d
commit 03299dcf5b
2 changed files with 6 additions and 2 deletions
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6
library/dhm.c
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@ -223,7 +223,8 @@ int mbedtls_dhm_make_params( mbedtls_dhm_context *ctx, int x_size,
goto cleanup;
/*
* export P, G, GX
* Export P, G, GX. RFC 5246 §4.4 states that "leading zero octets are
* not required". We omit leading zeros for compactness.
*/
#define DHM_MPI_EXPORT( X, n ) \
do { \
@ -436,8 +437,9 @@ int mbedtls_dhm_calc_secret( mbedtls_dhm_context *ctx,
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) );
}
/* Output the secret without any leading zero byte. This is mandatory
* for TLS per RFC 5246 §8.1.2. */
*olen = mbedtls_mpi_size( &ctx->K );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &ctx->K, output, *olen ) );
cleanup: