Add conditional assign and swap function for MPI modulus
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/bignum_mod_raw.c b/library/bignum_mod_raw.c
index 8c89b2c..f04354d 100644
--- a/library/bignum_mod_raw.c
+++ b/library/bignum_mod_raw.c
@@ -41,6 +41,24 @@
#include "bignum_mod.h"
#include "constant_time_internal.h"
+int mbedtls_mpi_mod_raw_cond_assign( mbedtls_mpi_uint *X,
+ mbedtls_mpi_uint *Y,
+ const mbedtls_mpi_mod_modulus *m,
+ unsigned char assign )
+{
+ return mbedtls_mpi_core_cond_assign( X, m->limbs,
+ Y, m->limbs, assign );
+}
+
+int mbedtls_mpi_mod_raw_cond_swap( mbedtls_mpi_uint *X,
+ mbedtls_mpi_uint *Y,
+ const mbedtls_mpi_mod_modulus *m,
+ unsigned char swap )
+{
+ return mbedtls_mpi_core_cond_swap( X, m->limbs,
+ Y, m->limbs, swap );
+}
+
int mbedtls_mpi_mod_raw_read( mbedtls_mpi_uint *X,
const mbedtls_mpi_mod_modulus *m,
const unsigned char *input,
diff --git a/library/bignum_mod_raw.h b/library/bignum_mod_raw.h
index 7b3a0c1..00ec921 100644
--- a/library/bignum_mod_raw.h
+++ b/library/bignum_mod_raw.h
@@ -33,6 +33,63 @@
#include "bignum_mod.h"
+/**
+ * \brief Perform a safe conditional copy of MPI which doesn't reveal whether
+ * the condition was true or not.
+ *
+ * \param[OUT] X The address of the first MPI. This must be initialized.
+ * \param[IN] Y The address of the second MPI. This must be initialized.
+ * \param[IN] m The address of the modulus related to \p X and \p Y.
+ * \param assign The condition deciding whether to perform the
+ * assignment or not. Must be either 0 or 1:
+ * * \c 1: Perform the assignment `X = Y`.
+ * * \c 0: Keep the original value of \p X.
+ *
+ * \note This function avoids leaking any information about whether
+ * the assignment was done or not.
+ *
+ * \warning If \p assign is neither 0 nor 1, the result of this function
+ * is indeterminate, and the resulting value in \p X might be
+ * neither its original value nor the value in \p Y.
+ *
+ * \return \c 0 if successful.
+ * \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
+ * large enough to hold the value in \p Y.
+ * \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
+ */
+int mbedtls_mpi_mod_raw_cond_assign( mbedtls_mpi_uint *X,
+ mbedtls_mpi_uint *Y,
+ const mbedtls_mpi_mod_modulus *m,
+ unsigned char assign );
+
+/**
+ * \brief Perform a safe conditional copy of MPI which doesn't reveal whether
+ * the condition was true or not.
+ *
+ * \param[IN,OUT] X The address of the first MPI. This must be initialized.
+ * \param[IN,OUT] Y The address of the second MPI. This must be initialized.
+ * \param[IN] m The address of the modulus related to \p X and \p Y.
+ * \param swap The condition deciding whether to perform
+ * the swap or not. Must be either 0 or 1:
+ * * \c 1: Swap the values of \p X and \p Y.
+ * * \c 0: Keep the original values of \p X and \p Y.
+ *
+ * \note This function avoids leaking any information about whether
+ * the swap was done or not.
+ *
+ * \warning If \p swap is neither 0 nor 1, the result of this function
+ * is indeterminate, and both \p X and \p Y might end up with
+ * values different to either of the original ones.
+ *
+ * \return \c 0 if successful.
+ * \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if the size of
+ * \p X and \p Y is differ.
+ * \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p X or \p Y is invalid.
+ */int mbedtls_mpi_mod_raw_cond_swap( mbedtls_mpi_uint *X,
+ mbedtls_mpi_uint *Y,
+ const mbedtls_mpi_mod_modulus *m,
+ unsigned char swap );
+
/** Import X from unsigned binary data.
*
* The MPI needs to have enough limbs to store the full value (including any