mbedtls/tests/suites/test_suite_bignum_mod.function

/* BEGIN_HEADER */
#include "mbedtls/bignum.h"
#include "mbedtls/entropy.h"
#include "bignum_mod.h"
#include "bignum_mod_raw.h"
#include "constant_time_internal.h"
#include "test/constant_flow.h"

#define TEST_COMPARE_MPI_RESIDUES( a, b ) \
            ASSERT_COMPARE( (a).p, (a).limbs * sizeof(mbedtls_mpi_uint), \
                            (b).p, (b).limbs * sizeof(mbedtls_mpi_uint) )

static int test_read_modulus( mbedtls_mpi_mod_modulus *m,
                              mbedtls_mpi_mod_rep_selector int_rep,
                              char *input )
{
    mbedtls_mpi_uint *p = NULL;
    size_t limbs;

    int ret = mbedtls_test_read_mpi_core( &p, &limbs, input );
    if( ret != 0 )
        return( ret );

    return( mbedtls_mpi_mod_modulus_setup( m, p, limbs, int_rep ) );
}

static int test_read_residue( mbedtls_mpi_mod_residue *r,
                              const mbedtls_mpi_mod_modulus *m,
                              char *input,
                              int skip_limbs_and_value_checks )
{
    mbedtls_mpi_uint *p = NULL;
    size_t limbs;

    int ret = mbedtls_test_read_mpi_core( &p, &limbs, input );
    if( ret != 0 )
        return( ret );

    if( skip_limbs_and_value_checks )
    {
        r->p = p;
        r->limbs = limbs;
        return( 0 );
    }

    /* mbedtls_mpi_mod_residue_setup() checks limbs, and that value < m */
    return( mbedtls_mpi_mod_residue_setup( r, m, p, limbs ) );
}
/* END_HEADER */

/* BEGIN_DEPENDENCIES
 * depends_on:MBEDTLS_BIGNUM_C
 * END_DEPENDENCIES
 */

/* BEGIN_CASE */
void mpi_mod_setup( int int_rep, int iret )
{
    #define MLIMBS 8
    mbedtls_mpi_uint mp[MLIMBS];
    mbedtls_mpi_mod_modulus m;
    int ret;

    memset( mp, 0xFF, sizeof(mp) );

    mbedtls_mpi_mod_modulus_init( &m );
    ret = mbedtls_mpi_mod_modulus_setup( &m, mp, MLIMBS, int_rep );
    TEST_EQUAL( ret, iret );

    /* Only test if the constants have been set-up  */
    if ( ret == 0 && int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY )
    {
        /* Test that the consts have been calculated */
        TEST_ASSERT( m.rep.mont.rr != NULL );
        TEST_ASSERT( m.rep.mont.mm != 0 );

    }

    /* Address sanitiser should catch if we try to free mp */
    mbedtls_mpi_mod_modulus_free( &m );

    /* Make sure that the modulus doesn't have reference to mp anymore */
    TEST_ASSERT( m.p != mp );

    /* Only test if the constants have been set-up  */
    if ( ret == 0 && int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY )
    {
        /* Verify the data and pointers allocated have been properly wiped */
        TEST_ASSERT( m.rep.mont.rr == NULL );
        TEST_ASSERT( m.rep.mont.mm == 0 );
    }
exit:
    /* It should be safe to call an mbedtls free several times */
    mbedtls_mpi_mod_modulus_free( &m );

    #undef MLIMBS
}
/* END_CASE */

/* BEGIN MERGE SLOT 1 */

/* END MERGE SLOT 1 */

/* BEGIN MERGE SLOT 2 */

/* BEGIN_CASE */
void mpi_mod_mul( char * input_A,
                  char * input_B,
                  char * input_N,
                  char * result )
{
    mbedtls_mpi_uint *X = NULL;

    mbedtls_mpi_mod_residue rA = { NULL, 0 };
    mbedtls_mpi_mod_residue rB = { NULL, 0 };
    mbedtls_mpi_mod_residue rR = { NULL, 0 };
    mbedtls_mpi_mod_residue rX = { NULL, 0 };

    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_modulus_init( &m );

    TEST_EQUAL( test_read_modulus( &m, MBEDTLS_MPI_MOD_REP_MONTGOMERY, input_N ),
                0 );

    TEST_EQUAL( test_read_residue( &rA, &m, input_A, 0 ), 0 );
    TEST_EQUAL( test_read_residue( &rB, &m, input_B, 0 ), 0 );
    TEST_EQUAL( test_read_residue( &rR, &m, result,  0 ), 0 );

    const size_t limbs = m.limbs;
    const size_t bytes = limbs * sizeof( mbedtls_mpi_uint );

    TEST_EQUAL( rA.limbs, limbs );
    TEST_EQUAL( rB.limbs, limbs );
    TEST_EQUAL( rR.limbs, limbs );

    ASSERT_ALLOC( X, limbs );

    TEST_EQUAL( mbedtls_mpi_mod_residue_setup( &rX, &m, X, limbs ), 0 );

    TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rA, &rB, &m ), 0 );
    ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

    /* alias X to A */
    memcpy( rX.p, rA.p, bytes );
    TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rX, &rB, &m ), 0 );
    ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

    /* alias X to B */
    memcpy( rX.p, rB.p, bytes );
    TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rA, &rX, &m ), 0);
    ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

    /* A == B: alias A and B */
    if( memcmp( rA.p, rB.p, bytes ) == 0 )
    {
        TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rA, &rA, &m ), 0 );
        ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

        /* X, A, B all aliased together */
        memcpy( rX.p, rA.p, bytes );
        TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rX, &rX, &m ), 0 );
        ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );
    }

    /* A != B: test B * A */
    else
    {
        TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rB, &rA, &m ), 0 );
        ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

        /* B * A: alias X to A */
        memcpy( rX.p, rA.p, bytes );
        TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rB, &rX, &m ), 0 );
        ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );

        /* B + A: alias X to B */
        memcpy( rX.p, rB.p, bytes );
        TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rX, &rA, &m ), 0 );
        ASSERT_COMPARE( rX.p, bytes, rR.p, bytes );
    }

exit:
    mbedtls_free( rA.p );
    mbedtls_free( rB.p );
    mbedtls_free( rR.p );
    mbedtls_free( X );
    mbedtls_free( (mbedtls_mpi_uint *) m.p );

    mbedtls_mpi_mod_modulus_free( &m );
}
/* END_CASE */

/* BEGIN_CASE */
void mpi_mod_mul_neg( char * input_A,
                      char * input_B,
                      char * input_N,
                      char * result,
                      int exp_ret )
{
    mbedtls_mpi_uint *X = NULL;

    mbedtls_mpi_mod_residue rA = { NULL, 0 };
    mbedtls_mpi_mod_residue rB = { NULL, 0 };
    mbedtls_mpi_mod_residue rR = { NULL, 0 };
    mbedtls_mpi_mod_residue rX = { NULL, 0 };

    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_modulus_init( &m );

    mbedtls_mpi_mod_modulus fake_m;
    mbedtls_mpi_mod_modulus_init( &fake_m );

    TEST_EQUAL( test_read_modulus( &m, MBEDTLS_MPI_MOD_REP_MONTGOMERY, input_N ),
                0 );

    TEST_EQUAL( test_read_residue( &rA, &m, input_A, 1 ), 0 );
    TEST_EQUAL( test_read_residue( &rB, &m, input_B, 1 ), 0 );
    TEST_EQUAL( test_read_residue( &rR, &m, result,  1 ), 0 );

    const size_t limbs = m.limbs;

    ASSERT_ALLOC( X, limbs );

    TEST_EQUAL( mbedtls_mpi_mod_residue_setup( &rX, &m, X, limbs ), 0 );
    rX.limbs = rR.limbs;

    TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rA, &rB, &m ), exp_ret );

    /* Check when m is not initialized */
    TEST_EQUAL( mbedtls_mpi_mod_mul( &rX, &rA, &rB, &fake_m ),
                MBEDTLS_ERR_MPI_BAD_INPUT_DATA );

exit:
    mbedtls_free( rA.p );
    mbedtls_free( rB.p );
    mbedtls_free( rR.p );
    mbedtls_free( X );
    mbedtls_free( (mbedtls_mpi_uint *) m.p );

    mbedtls_mpi_mod_modulus_free( &m );
    mbedtls_mpi_mod_modulus_free( &fake_m );
}
/* END_CASE */

/* END MERGE SLOT 2 */

/* BEGIN MERGE SLOT 3 */
/* BEGIN_CASE */
void mpi_mod_sub( char * input_N,
                  char * input_A, char * input_B,
                  char * input_D, int expected_ret )
{
    mbedtls_mpi_mod_residue a = { NULL, 0 };
    mbedtls_mpi_mod_residue b = { NULL, 0 };
    mbedtls_mpi_mod_residue d = { NULL, 0 };
    mbedtls_mpi_mod_residue x = { NULL, 0 };
    mbedtls_mpi_uint *X_raw = NULL;

    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_modulus_init( &m );

    TEST_EQUAL( 0,
        test_read_modulus( &m, MBEDTLS_MPI_MOD_REP_MONTGOMERY, input_N ) );

    /* test_read_residue() normally checks that inputs have the same number of
     * limbs as the modulus. For negative testing we can ask it to skip this
     * with a non-zero final parameter. */
    TEST_EQUAL( 0, test_read_residue( &a, &m, input_A, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &b, &m, input_B, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &d, &m, input_D, expected_ret != 0 ) );

    size_t limbs = m.limbs;
    size_t bytes = limbs * sizeof( *X_raw );

    if( expected_ret == 0 )
    {
        /* Negative test with too many limbs in output */
        ASSERT_ALLOC( X_raw, limbs + 1 );

        x.p = X_raw;
        x.limbs = limbs + 1;
        TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                    mbedtls_mpi_mod_sub( &x, &a, &b, &m ) );

        mbedtls_free( X_raw );
        X_raw = NULL;

        /* Negative test with too few limbs in output */
        if( limbs > 1 )
        {
            ASSERT_ALLOC( X_raw, limbs - 1 );

            x.p = X_raw;
            x.limbs = limbs - 1;
            TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                        mbedtls_mpi_mod_sub( &x, &a, &b, &m ) );

            mbedtls_free( X_raw );
            X_raw = NULL;
        }

        /* Negative testing with too many/too few limbs in a and b is covered by
         * manually-written test cases with expected_ret != 0. */
    }

    ASSERT_ALLOC( X_raw, limbs );

    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &x, &m, X_raw, limbs ) );

    /* a - b => Correct result, or expected error */
    TEST_EQUAL( expected_ret, mbedtls_mpi_mod_sub( &x, &a, &b, &m ) );
    if( expected_ret != 0 )
        goto exit;

    TEST_COMPARE_MPI_RESIDUES( x, d );

    /* a - b: alias x to a => Correct result */
    memcpy( x.p, a.p, bytes );
    TEST_EQUAL( 0, mbedtls_mpi_mod_sub( &x, &x, &b, &m ) );
    TEST_COMPARE_MPI_RESIDUES( x, d );

    /* a - b: alias x to b => Correct result */
    memcpy( x.p, b.p, bytes );
    TEST_EQUAL( 0, mbedtls_mpi_mod_sub( &x, &a, &x, &m ) );
    TEST_COMPARE_MPI_RESIDUES( x, d );

    if ( memcmp( a.p, b.p, bytes ) == 0 )
    {
        /* a == b: alias a and b */

        /* a - a => Correct result */
        TEST_EQUAL( 0, mbedtls_mpi_mod_sub( &x, &a, &a, &m ) );
        TEST_COMPARE_MPI_RESIDUES( x, d );

        /* a - a: x, a, b all aliased together => Correct result */
        memcpy( x.p, a.p, bytes );
        TEST_EQUAL( 0, mbedtls_mpi_mod_sub( &x, &x, &x, &m ) );
        TEST_COMPARE_MPI_RESIDUES( x, d );
    }

exit:
    mbedtls_free( (void *)m.p ); /* mbedtls_mpi_mod_modulus_free() sets m.p = NULL */
    mbedtls_mpi_mod_modulus_free( &m );

    mbedtls_free( a.p );
    mbedtls_free( b.p );
    mbedtls_free( d.p );
    mbedtls_free( X_raw );
}
/* END_CASE */

/* BEGIN_CASE */
void mpi_mod_inv_mont( char * input_N,
                       char * input_A, char * input_I,
                       int expected_ret )
{
    mbedtls_mpi_mod_residue a = { NULL, 0 };    /* argument */
    mbedtls_mpi_mod_residue i = { NULL, 0 };    /* expected inverse wrt N */
    mbedtls_mpi_mod_residue x = { NULL, 0 };    /* output */
    mbedtls_mpi_uint *X_raw = NULL;

    mbedtls_mpi_mod_modulus N;
    mbedtls_mpi_mod_modulus_init( &N );

    TEST_EQUAL( 0,
        test_read_modulus( &N, MBEDTLS_MPI_MOD_REP_MONTGOMERY, input_N ) );

    /* test_read_residue() normally checks that inputs have the same number of
     * limbs as the modulus. For negative testing we can ask it to skip this
     * with a non-zero final parameter. */
    TEST_EQUAL( 0, test_read_residue( &a, &N, input_A, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &i, &N, input_I, expected_ret != 0 ) );

    size_t limbs = N.limbs;
    size_t bytes = limbs * sizeof( *X_raw );

    ASSERT_ALLOC( X_raw, limbs );

    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &x, &N, X_raw, limbs ) );

    TEST_EQUAL( expected_ret, mbedtls_mpi_mod_inv( &x, &a, &N ) );
    if( expected_ret == 0 )
    {
        TEST_COMPARE_MPI_RESIDUES( x, i );

        /* a^-1: alias x to a => Correct result */
        memcpy( x.p, a.p, bytes );
        TEST_EQUAL( 0, mbedtls_mpi_mod_inv( &x, &x, &N ) );
        TEST_COMPARE_MPI_RESIDUES( x, i );
    }

exit:
    mbedtls_free( (void *)N.p ); /* mbedtls_mpi_mod_modulus_free() sets N.p = NULL */
    mbedtls_mpi_mod_modulus_free( &N );

    mbedtls_free( a.p );
    mbedtls_free( i.p );
    mbedtls_free( X_raw );
}
/* END_CASE */

/* BEGIN_CASE */
void mpi_mod_inv_non_mont( char * input_N,
                           char * input_A, char * input_I,
                           int expected_ret )
{
    mbedtls_mpi_mod_residue a = { NULL, 0 };    /* argument */
    mbedtls_mpi_mod_residue i = { NULL, 0 };    /* expected inverse wrt N */
    mbedtls_mpi_mod_residue x = { NULL, 0 };    /* output */
    mbedtls_mpi_uint *X_raw = NULL;

    mbedtls_mpi_mod_modulus N;
    mbedtls_mpi_mod_modulus_init( &N );

    TEST_EQUAL( 0,
        test_read_modulus( &N, MBEDTLS_MPI_MOD_REP_OPT_RED, input_N ) );

    /* test_read_residue() normally checks that inputs have the same number of
     * limbs as the modulus. For negative testing we can ask it to skip this
     * with a non-zero final parameter. */
    TEST_EQUAL( 0, test_read_residue( &a, &N, input_A, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &i, &N, input_I, expected_ret != 0 ) );

    size_t limbs = N.limbs;
    size_t bytes = limbs * sizeof( *X_raw );

    ASSERT_ALLOC( X_raw, limbs );

    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &x, &N, X_raw, limbs ) );

    TEST_EQUAL( expected_ret, mbedtls_mpi_mod_inv( &x, &a, &N ) );
    if( expected_ret == 0 )
    {
        TEST_COMPARE_MPI_RESIDUES( x, i );

        /* a^-1: alias x to a => Correct result */
        memcpy( x.p, a.p, bytes );
        TEST_EQUAL( 0, mbedtls_mpi_mod_inv( &x, &x, &N ) );
        TEST_COMPARE_MPI_RESIDUES( x, i );
    }

exit:
    mbedtls_free( (void *)N.p ); /* mbedtls_mpi_mod_modulus_free() sets N.p = NULL */
    mbedtls_mpi_mod_modulus_free( &N );

    mbedtls_free( a.p );
    mbedtls_free( i.p );
    mbedtls_free( X_raw );
}
/* END_CASE */
/* END MERGE SLOT 3 */

/* BEGIN MERGE SLOT 4 */

/* END MERGE SLOT 4 */

/* BEGIN MERGE SLOT 5 */
/* BEGIN_CASE */
void mpi_mod_add( char * input_N,
                  char * input_A, char * input_B,
                  char * input_S, int expected_ret )
{
    mbedtls_mpi_mod_residue a = { NULL, 0 };
    mbedtls_mpi_mod_residue b = { NULL, 0 };
    mbedtls_mpi_mod_residue s = { NULL, 0 };
    mbedtls_mpi_mod_residue x = { NULL, 0 };
    mbedtls_mpi_uint *X_raw = NULL;

    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_modulus_init( &m );

    TEST_EQUAL( 0,
        test_read_modulus( &m, MBEDTLS_MPI_MOD_REP_MONTGOMERY, input_N ) );

    /* test_read_residue() normally checks that inputs have the same number of
     * limbs as the modulus. For negative testing we can ask it to skip this
     * with a non-zero final parameter. */
    TEST_EQUAL( 0, test_read_residue( &a, &m, input_A, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &b, &m, input_B, expected_ret != 0 ) );
    TEST_EQUAL( 0, test_read_residue( &s, &m, input_S, expected_ret != 0 ) );

    size_t limbs = m.limbs;
    size_t bytes = limbs * sizeof( *X_raw );

    if( expected_ret == 0 )
    {
        /* Negative test with too many limbs in output */
        ASSERT_ALLOC( X_raw, limbs + 1 );

        x.p = X_raw;
        x.limbs = limbs + 1;
        TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                    mbedtls_mpi_mod_add( &x, &a, &b, &m ) );

        mbedtls_free( X_raw );
        X_raw = NULL;

        /* Negative test with too few limbs in output */
        if( limbs > 1 )
        {
            ASSERT_ALLOC( X_raw, limbs - 1 );

            x.p = X_raw;
            x.limbs = limbs - 1;
            TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                        mbedtls_mpi_mod_add( &x, &a, &b, &m ) );

            mbedtls_free( X_raw );
            X_raw = NULL;
        }

        /* Negative testing with too many/too few limbs in a and b is covered by
         * manually-written test cases with oret != 0. */
    }

    /* Allocate correct number of limbs for X_raw */
    ASSERT_ALLOC( X_raw, limbs );

    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &x, &m, X_raw, limbs ) );

    /* A + B => Correct result or expected error */
    TEST_EQUAL( expected_ret, mbedtls_mpi_mod_add( &x, &a, &b, &m ) );
    if( expected_ret != 0 )
        goto exit;

    TEST_COMPARE_MPI_RESIDUES( x, s );

    /* a + b: alias x to a => Correct result */
    memcpy( x.p, a.p, bytes );
    TEST_EQUAL( 0, mbedtls_mpi_mod_add( &x, &x, &b, &m ) );
    TEST_COMPARE_MPI_RESIDUES( x, s );

    /* a + b: alias x to b => Correct result */
    memcpy( x.p, b.p, bytes );
    TEST_EQUAL( 0, mbedtls_mpi_mod_add( &x, &a, &x, &m ) );
    TEST_COMPARE_MPI_RESIDUES( x, s );

    if ( memcmp( a.p, b.p, bytes ) == 0 )
    {
        /* a == b: alias a and b */

        /* a + a => Correct result */
        TEST_EQUAL( 0, mbedtls_mpi_mod_add( &x, &a, &a, &m ) );
        TEST_COMPARE_MPI_RESIDUES( x, s );

        /* a + a: x, a, b all aliased together => Correct result */
        memcpy( x.p, a.p, bytes );
        TEST_EQUAL( 0, mbedtls_mpi_mod_add( &x, &x, &x, &m ) );
        TEST_COMPARE_MPI_RESIDUES( x, s );
    }

exit:
    mbedtls_free( (void *)m.p ); /* mbedtls_mpi_mod_modulus_free() sets m.p = NULL */
    mbedtls_mpi_mod_modulus_free( &m );

    mbedtls_free( a.p );
    mbedtls_free( b.p );
    mbedtls_free( s.p );
    mbedtls_free( X_raw );
}
/* END_CASE */
/* END MERGE SLOT 5 */

/* BEGIN MERGE SLOT 6 */

/* END MERGE SLOT 6 */

/* BEGIN MERGE SLOT 7 */
/* BEGIN_CASE */
void mpi_residue_setup( char * input_N, char * input_R, int ret )
{
    mbedtls_mpi_uint *N = NULL;
    mbedtls_mpi_uint *R = NULL;
    size_t n_limbs, r_limbs;
    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_residue r;

    mbedtls_mpi_mod_modulus_init( &m );

    /* Allocate the memory for intermediate data structures */
    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, input_N ) );
    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R, &r_limbs, input_R ) );

    TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs,
                MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );

    TEST_EQUAL( ret, mbedtls_mpi_mod_residue_setup( &r, &m, R , r_limbs ) );

    if ( ret == 0 )
    {
        TEST_EQUAL( r.limbs, r_limbs );
        TEST_ASSERT( r.p == R );
    }

exit:
    mbedtls_mpi_mod_modulus_free( &m );
    mbedtls_free( N );
    mbedtls_free( R );
}
/* END_CASE */

/* BEGIN_CASE */
void mpi_mod_io_neg( char * input_N, data_t * buf, int ret )
{
    mbedtls_mpi_uint *N = NULL;
    mbedtls_mpi_uint *R = NULL;

    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_residue r = { NULL, 0 };
    mbedtls_mpi_mod_ext_rep endian = MBEDTLS_MPI_MOD_EXT_REP_LE;

    mbedtls_mpi_mod_modulus_init( &m );

    size_t n_limbs;
    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, input_N ) );
    size_t r_limbs = n_limbs;
    ASSERT_ALLOC( R, r_limbs );

    /* modulus->p == NULL || residue->p == NULL ( m has not been set-up ) */
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_read( &r, &m, buf->x, buf->len, endian ) );

    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_write( &r, &m, buf->x, buf->len, endian ) );

    /* Set up modulus and test with residue->p == NULL */
    TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs,
                MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );

    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_read( &r, &m, buf->x, buf->len, endian ) );
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_write( &r, &m, buf->x, buf->len, endian ) );

    /* Do the rest of the tests with a residue set up with the input data */
    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R , r_limbs ) );

    /* Fail for r_limbs < m->limbs */
    r.limbs--;
    TEST_ASSERT( r.limbs < m.limbs );
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_read( &r, &m, buf->x, buf->len, endian ) );
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_write( &r, &m, buf->x, buf->len, endian ) );
    r.limbs++;

    /* Fail for r_limbs > m->limbs */
    m.limbs--;
    TEST_ASSERT( r.limbs > m.limbs );
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_read( &r, &m, buf->x, buf->len, endian ) );
    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
                mbedtls_mpi_mod_write( &r, &m, buf->x, buf->len, endian ) );
    m.limbs++;

    /* Test the read */
    TEST_EQUAL( ret, mbedtls_mpi_mod_read( &r, &m, buf->x, buf->len, endian ) );

    /* Test write overflow only when the representation is large and read is successful  */
    if ( r.limbs > 1 && ret == 0 )
        TEST_EQUAL( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL,
                        mbedtls_mpi_mod_write( &r, &m, buf->x, 1, endian ) );

exit:
    mbedtls_mpi_mod_residue_release( &r );
    mbedtls_mpi_mod_modulus_free( &m );
    mbedtls_free( N );
    mbedtls_free( R );
}
/* END_CASE */

/* BEGIN_CASE */
void mpi_mod_io( char * input_N, data_t * input_A, int endian )
{
    mbedtls_mpi_uint *N = NULL;
    mbedtls_mpi_uint *R = NULL;
    mbedtls_mpi_uint *R_COPY = NULL;
    unsigned char *obuf = NULL;
    unsigned char *ref_buf = NULL;
    mbedtls_mpi_mod_modulus m;
    mbedtls_mpi_mod_residue r;
    mbedtls_mpi_mod_residue r_copy;
    size_t n_limbs, n_bytes, a_bytes;

    mbedtls_mpi_mod_modulus_init( &m );

    /* Read inputs */
    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, input_N ) );
    n_bytes = n_limbs * sizeof( mbedtls_mpi_uint );
    a_bytes = input_A->len;

    /* Allocate the memory for intermediate data structures */
    ASSERT_ALLOC( R, n_bytes );
    ASSERT_ALLOC( R_COPY, n_bytes );

    /* Test that input's size is not greater to modulo's */
    TEST_LE_U( a_bytes, n_bytes );

    /* Init Structures */
    TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs,
                MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );

    /* Enforcing p_limbs >= m->limbs */
    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R, n_limbs ) );

    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, input_A->x, input_A->len,
                                         endian ) );

    /* Read a copy for checking that writing didn't change the value of r */
    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r_copy, &m,
                                                  R_COPY, n_limbs ) );
    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r_copy, &m, input_A->x, input_A->len,
                                         endian ) );

    /* Get number of bytes without leading zeroes */
    size_t a_bytes_trimmed = a_bytes;
    while( a_bytes_trimmed > 0 )
    {
        unsigned char* r_byte_array = (unsigned char*) r.p;
        if( r_byte_array[--a_bytes_trimmed] != 0 )
            break;
    }
    a_bytes_trimmed++;

    /* Test write with three output buffer sizes: tight, same as input and
     * longer than the input */
    size_t obuf_sizes[3];
    const size_t obuf_sizes_len = sizeof( obuf_sizes ) / sizeof( obuf_sizes[0] );
    obuf_sizes[0] = a_bytes_trimmed;
    obuf_sizes[1] = a_bytes;
    obuf_sizes[2] = a_bytes + 8;

    for( size_t i = 0; i < obuf_sizes_len; i++ )
    {
        ASSERT_ALLOC( obuf, obuf_sizes[i] );
        TEST_EQUAL( 0, mbedtls_mpi_mod_write( &r, &m, obuf, obuf_sizes[i], endian ) );

        /* Make sure that writing didn't corrupt the value of r */
        ASSERT_COMPARE( r.p, r.limbs, r_copy.p, r_copy.limbs );

        /* Set up reference output for checking the result */
        ASSERT_ALLOC( ref_buf, obuf_sizes[i] );
        switch( endian )
        {
            case MBEDTLS_MPI_MOD_EXT_REP_LE:
                memcpy( ref_buf, input_A->x, a_bytes_trimmed );
                break;
            case MBEDTLS_MPI_MOD_EXT_REP_BE:
                {
                    size_t a_offset = input_A->len - a_bytes_trimmed;
                    size_t ref_offset = obuf_sizes[i] - a_bytes_trimmed;
                    memcpy( ref_buf + ref_offset, input_A->x + a_offset,
                            a_bytes_trimmed );
                }
                break;
            default:
                TEST_ASSERT( 0 );
        }

        /* Check the result */
        ASSERT_COMPARE( obuf, obuf_sizes[i], ref_buf, obuf_sizes[i] );

        mbedtls_free( ref_buf );
        ref_buf = NULL;
        mbedtls_free( obuf );
        obuf = NULL;
    }

exit:
    mbedtls_mpi_mod_modulus_free( &m );
    mbedtls_free( N );
    mbedtls_free( R );
    mbedtls_free( R_COPY );
    mbedtls_free( obuf );
}
/* END_CASE */
/* END MERGE SLOT 7 */

/* BEGIN MERGE SLOT 8 */

/* END MERGE SLOT 8 */

/* BEGIN MERGE SLOT 9 */

/* END MERGE SLOT 9 */

/* BEGIN MERGE SLOT 10 */

/* END MERGE SLOT 10 */