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+/**
+ * \file rsa_alt_helpers.h
+ *
+ * \brief Context-independent RSA helper functions
+ *
+ * This module declares some RSA-related helper functions useful when
+ * implementing the RSA interface. These functions are provided in a separate
+ * compilation unit in order to make it easy for designers of alternative RSA
+ * implementations to use them in their own code, as it is conceived that the
+ * functionality they provide will be necessary for most complete
+ * implementations.
+ *
+ * End-users of Mbed TLS who are not providing their own alternative RSA
+ * implementations should not use these functions directly, and should instead
+ * use only the functions declared in rsa.h.
+ *
+ * The interface provided by this module will be maintained through LTS (Long
+ * Term Support) branches of Mbed TLS, but may otherwise be subject to change,
+ * and must be considered an internal interface of the library.
+ *
+ * There are two classes of helper functions:
+ *
+ * (1) Parameter-generating helpers. These are:
+ * - mbedtls_rsa_deduce_primes
+ * - mbedtls_rsa_deduce_private_exponent
+ * - mbedtls_rsa_deduce_crt
+ * Each of these functions takes a set of core RSA parameters and
+ * generates some other, or CRT related parameters.
+ *
+ * (2) Parameter-checking helpers. These are:
+ * - mbedtls_rsa_validate_params
+ * - mbedtls_rsa_validate_crt
+ * They take a set of core or CRT related RSA parameters and check their
+ * validity.
+ *
+ */
+/*
+ * Copyright The Mbed TLS Contributors
+ * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+#ifndef MBEDTLS_RSA_ALT_HELPERS_H
+#define MBEDTLS_RSA_ALT_HELPERS_H
+
+#include "mbedtls/build_info.h"
+
+#include "mbedtls/bignum.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/**
+ * \brief Compute RSA prime moduli P, Q from public modulus N=PQ
+ * and a pair of private and public key.
+ *
+ * \note This is a 'static' helper function not operating on
+ * an RSA context. Alternative implementations need not
+ * overwrite it.
+ *
+ * \param N RSA modulus N = PQ, with P, Q to be found
+ * \param E RSA public exponent
+ * \param D RSA private exponent
+ * \param P Pointer to MPI holding first prime factor of N on success
+ * \param Q Pointer to MPI holding second prime factor of N on success
+ *
+ * \return
+ * - 0 if successful. In this case, P and Q constitute a
+ * factorization of N.
+ * - A non-zero error code otherwise.
+ *
+ * \note It is neither checked that P, Q are prime nor that
+ * D, E are modular inverses wrt. P-1 and Q-1. For that,
+ * use the helper function \c mbedtls_rsa_validate_params.
+ *
+ */
+int mbedtls_rsa_deduce_primes(mbedtls_mpi const *N, mbedtls_mpi const *E,
+ mbedtls_mpi const *D,
+ mbedtls_mpi *P, mbedtls_mpi *Q);
+
+/**
+ * \brief Compute RSA private exponent from
+ * prime moduli and public key.
+ *
+ * \note This is a 'static' helper function not operating on
+ * an RSA context. Alternative implementations need not
+ * overwrite it.
+ *
+ * \param P First prime factor of RSA modulus
+ * \param Q Second prime factor of RSA modulus
+ * \param E RSA public exponent
+ * \param D Pointer to MPI holding the private exponent on success.
+ *
+ * \return
+ * - 0 if successful. In this case, D is set to a simultaneous
+ * modular inverse of E modulo both P-1 and Q-1.
+ * - A non-zero error code otherwise.
+ *
+ * \note This function does not check whether P and Q are primes.
+ *
+ */
+int mbedtls_rsa_deduce_private_exponent(mbedtls_mpi const *P,
+ mbedtls_mpi const *Q,
+ mbedtls_mpi const *E,
+ mbedtls_mpi *D);
+
+
+/**
+ * \brief Generate RSA-CRT parameters
+ *
+ * \note This is a 'static' helper function not operating on
+ * an RSA context. Alternative implementations need not
+ * overwrite it.
+ *
+ * \param P First prime factor of N
+ * \param Q Second prime factor of N
+ * \param D RSA private exponent
+ * \param DP Output variable for D modulo P-1
+ * \param DQ Output variable for D modulo Q-1
+ * \param QP Output variable for the modular inverse of Q modulo P.
+ *
+ * \return 0 on success, non-zero error code otherwise.
+ *
+ * \note This function does not check whether P, Q are
+ * prime and whether D is a valid private exponent.
+ *
+ */
+int mbedtls_rsa_deduce_crt(const mbedtls_mpi *P, const mbedtls_mpi *Q,
+ const mbedtls_mpi *D, mbedtls_mpi *DP,
+ mbedtls_mpi *DQ, mbedtls_mpi *QP);
+
+
+/**
+ * \brief Check validity of core RSA parameters
+ *
+ * \note This is a 'static' helper function not operating on
+ * an RSA context. Alternative implementations need not
+ * overwrite it.
+ *
+ * \param N RSA modulus N = PQ
+ * \param P First prime factor of N
+ * \param Q Second prime factor of N
+ * \param D RSA private exponent
+ * \param E RSA public exponent
+ * \param f_rng PRNG to be used for primality check, or NULL
+ * \param p_rng PRNG context for f_rng, or NULL
+ *
+ * \return
+ * - 0 if the following conditions are satisfied
+ * if all relevant parameters are provided:
+ * - P prime if f_rng != NULL (%)
+ * - Q prime if f_rng != NULL (%)
+ * - 1 < N = P * Q
+ * - 1 < D, E < N
+ * - D and E are modular inverses modulo P-1 and Q-1
+ * (%) This is only done if MBEDTLS_GENPRIME is defined.
+ * - A non-zero error code otherwise.
+ *
+ * \note The function can be used with a restricted set of arguments
+ * to perform specific checks only. E.g., calling it with
+ * (-,P,-,-,-) and a PRNG amounts to a primality check for P.
+ */
+int mbedtls_rsa_validate_params(const mbedtls_mpi *N, const mbedtls_mpi *P,
+ const mbedtls_mpi *Q, const mbedtls_mpi *D,
+ const mbedtls_mpi *E,
+ int (*f_rng)(void *, unsigned char *, size_t),
+ void *p_rng);
+
+/**
+ * \brief Check validity of RSA CRT parameters
+ *
+ * \note This is a 'static' helper function not operating on
+ * an RSA context. Alternative implementations need not
+ * overwrite it.
+ *
+ * \param P First prime factor of RSA modulus
+ * \param Q Second prime factor of RSA modulus
+ * \param D RSA private exponent
+ * \param DP MPI to check for D modulo P-1
+ * \param DQ MPI to check for D modulo P-1
+ * \param QP MPI to check for the modular inverse of Q modulo P.
+ *
+ * \return
+ * - 0 if the following conditions are satisfied:
+ * - D = DP mod P-1 if P, D, DP != NULL
+ * - Q = DQ mod P-1 if P, D, DQ != NULL
+ * - QP = Q^-1 mod P if P, Q, QP != NULL
+ * - \c MBEDTLS_ERR_RSA_KEY_CHECK_FAILED if check failed,
+ * potentially including \c MBEDTLS_ERR_MPI_XXX if some
+ * MPI calculations failed.
+ * - \c MBEDTLS_ERR_RSA_BAD_INPUT_DATA if insufficient
+ * data was provided to check DP, DQ or QP.
+ *
+ * \note The function can be used with a restricted set of arguments
+ * to perform specific checks only. E.g., calling it with the
+ * parameters (P, -, D, DP, -, -) will check DP = D mod P-1.
+ */
+int mbedtls_rsa_validate_crt(const mbedtls_mpi *P, const mbedtls_mpi *Q,
+ const mbedtls_mpi *D, const mbedtls_mpi *DP,
+ const mbedtls_mpi *DQ, const mbedtls_mpi *QP);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* rsa_alt_helpers.h */