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Add mpi_safe_cond_swap()

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This commit is contained in:
Manuel Pégourié-Gonnard
2013-12-04 21:41:50 +01:00
parent 97871ef236
commit a60fe8943d
4 changed files with 110 additions and 7 deletions
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22
include/polarssl/bignum.h
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@@ -236,11 +236,10 @@ void mpi_swap( mpi *X, mpi *Y );
*
* \param X MPI to conditionally assign to
* \param Y Value to be assigned
* \param assign 1: perform the assignment, 0: leave X untouched
* \param assign 1: perform the assignment, 0: keep X's original value
*
* \return 0 if successful,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed,
* POLARSSL_ERR_MPI_BAD_INPUT_DATA if assing is not 0 or 1
*
* \note This function is equivalent to
* if( assign ) mpi_copy( X, Y );
@@ -251,6 +250,25 @@ void mpi_swap( mpi *X, mpi *Y );
*/
int mpi_safe_cond_assign( mpi *X, const mpi *Y, unsigned char assign );
/**
* \brief Safe conditional swap X <-> Y if swap is 1
*
* \param X First mpi value
* \param Y Second mpi value
* \param assign 1: perform the swap, 0: keep X and Y's original values
*
* \return 0 if successful,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed,
*
* \note This function is equivalent to
* if( assign ) mpi_swap( 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 and/or memory access
* patterns analysis).
*/
int mpi_safe_cond_swap( mpi *X, mpi *Y, unsigned char assign );
/**
* \brief Set value from integer
*