diff --git a/tests/include/test/bignum_helpers.h b/tests/include/test/bignum_helpers.h
new file mode 100644
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+++ b/tests/include/test/bignum_helpers.h
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+/**
+ * \file bignum_helpers.h
+ *
+ * \brief   This file contains the prototypes of helper functions for
+ *          bignum-related testing.
+ */
+
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+#ifndef TEST_BIGNUM_HELPERS_H
+#define TEST_BIGNUM_HELPERS_H
+
+#include <mbedtls/build_info.h>
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+#include <mbedtls/bignum.h>
+#include <bignum_mod.h>
+
+/** Allocate and populate a core MPI from a test case argument.
+ *
+ * This function allocates exactly as many limbs as necessary to fit
+ * the length of the input. In other words, it preserves leading zeros.
+ *
+ * The limb array is allocated with mbedtls_calloc() and must later be
+ * freed with mbedtls_free().
+ *
+ * \param[in,out] pX    The address where a pointer to the allocated limb
+ *                      array will be stored.
+ *                      \c *pX must be null on entry.
+ *                      On exit, \c *pX is null on error or if the number
+ *                      of limbs is 0.
+ * \param[out] plimbs   The address where the number of limbs will be stored.
+ * \param[in] input     The test argument to read.
+ *                      It is interpreted as a hexadecimal representation
+ *                      of a non-negative integer.
+ *
+ * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
+ */
+int mbedtls_test_read_mpi_core(mbedtls_mpi_uint **pX, size_t *plimbs,
+                               const char *input);
+
+/** Read a modulus from a hexadecimal string.
+ *
+ * This function allocates exactly as many limbs as necessary to fit
+ * the length of the input. In other words, it preserves leading zeros.
+ *
+ * The limb array is allocated with mbedtls_calloc() and must later be
+ * freed with mbedtls_free(). You can do that by calling
+ * mbedtls_test_mpi_mod_modulus_free_with_limbs().
+ *
+ * \param[in,out] N     A modulus structure. It must be initialized, but
+ *                      not set up.
+ * \param[in] s         The null-terminated hexadecimal string to read from.
+ * \param int_rep       The desired representation of residues.
+ *
+ * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
+ */
+int mbedtls_test_read_mpi_modulus(mbedtls_mpi_mod_modulus *N,
+                                  const char *s,
+                                  mbedtls_mpi_mod_rep_selector int_rep);
+
+/** Free a modulus and its limbs.
+ *
+ * \param[in] N         A modulus structure such that there is no other
+ *                      reference to `N->p`.
+ */
+void mbedtls_test_mpi_mod_modulus_free_with_limbs(mbedtls_mpi_mod_modulus *N);
+
+/** Read an MPI from a hexadecimal string.
+ *
+ * Like mbedtls_mpi_read_string(), but with tighter guarantees around
+ * edge cases.
+ *
+ * - This function guarantees that if \p s begins with '-' then the sign
+ *   bit of the result will be negative, even if the value is 0.
+ *   When this function encounters such a "negative 0", it calls
+ *   mbedtls_test_increment_case_uses_negative_0().
+ * - The size of the result is exactly the minimum number of limbs needed to fit
+ *   the digits in the input. In particular, this function constructs a bignum
+ *   with 0 limbs for an empty string, and a bignum with leading 0 limbs if the
+ *   string has sufficiently many leading 0 digits. This is important so that
+ *   the "0 (null)" and "0 (1 limb)" and "leading zeros" test cases do what they
+ *   claim.
+ *
+ * \param[out] X        The MPI object to populate. It must be initialized.
+ * \param[in] s         The null-terminated hexadecimal string to read from.
+ *
+ * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
+ */
+int mbedtls_test_read_mpi(mbedtls_mpi *X, const char *s);
+
+#endif /* MBEDTLS_BIGNUM_C */
+
+#endif /* TEST_BIGNUM_HELPERS_H */