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Make memory access pattern constant

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Manuel Pégourié-Gonnard 2013-11-21 20:00:38 +01:00
parent aade42fd88
commit d728350cee
3 changed files with 28 additions and 18 deletions
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3
include/polarssl/bignum.h
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@ -246,7 +246,8 @@ void mpi_swap( mpi *X, mpi *Y );
* if( assign ) mpi_copy( X, Y );
* except that it avoids leaking any information about whether
* the assignment was done or not (the above code may leak
* information through branch prediction analysis).
* information through branch prediction and/or memory access
* patterns analysis).
*/
int mpi_safe_cond_assign( mpi *X, mpi *Y, unsigned char assign );

14
include/polarssl/ecp.h
View file

@ -463,15 +463,15 @@ int ecp_sub( const ecp_group *grp, ecp_point *R,
* or P is not a valid pubkey,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
*
* \note In order to prevent simple timing attacks, this function
* executes a constant number of operations (that is, point
* doubling and addition of distinct points) for random m in
* the allowed range.
* \note In order to prevent timing attacks, this function
* executes the exact same sequence of (base field)
* operations for any valid m. It avoids any if-branch or
* array index depending on the value of m.
*
* \note If f_rng is not NULL, it is used to randomize intermediate
* results in order to prevent potential attacks targetting
* these results. It is recommended to always provide a
* non-NULL f_rng (the overhead is negligible).
* results in order to prevent potential timing attacks
* targetting these results. It is recommended to always
* provide a non-NULL f_rng (the overhead is negligible).
*/
int ecp_mul( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,