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Improved on the previous fix and added a test case to cover both types

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of carries.
This commit is contained in:
Janos Follath
2015-10-30 17:43:11 +01:00
parent 3fc644f246
commit 6c92268093
2 changed files with 10 additions and 18 deletions
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25
library/bignum.c
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@ -858,22 +858,11 @@ int mbedtls_mpi_add_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
{
int ret;
size_t i, j;
mbedtls_mpi_uint *o, *p, c;
mbedtls_mpi TB;
mbedtls_mpi_uint *o, *p, c, tmp;
if( X == B )
{
B = A; A = X;
if( B == A )
{
// Making a temporary copy instead of shifting by one to deny
// the possibility of corresponding side-channel attacks.
mbedtls_mpi_init( &TB );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &TB, B ) );
B = &TB;
}
const mbedtls_mpi *T = A; A = X; B = T;
}
if( X != A )
@ -892,10 +881,14 @@ int mbedtls_mpi_add_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
o = B->p; p = X->p; c = 0;
/*
* tmp is used because it might happen that p == o
*/
for( i = 0; i < j; i++, o++, p++ )
{
tmp= *o;
*p += c; c = ( *p < c );
*p += *o; c += ( *p < *o );
*p += tmp; c += ( *p < tmp );
}
while( c != 0 )
@ -910,10 +903,6 @@ int mbedtls_mpi_add_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
}
cleanup:
if( &TB == B )
{
mbedtls_mpi_free( &TB );
}
return( ret );
}