Introduce new files rsa_internal.[ch] for RSA helper functions
This commit splits off the RSA helper functions into separate headers and
compilation units to have a clearer separation of the public RSA interface,
intended to be used by end-users, and the helper functions which are publicly
provided only for the benefit of designers of alternative RSA implementations.
diff --git a/include/mbedtls/rsa_internal.h b/include/mbedtls/rsa_internal.h
new file mode 100644
index 0000000..2353470
--- /dev/null
+++ b/include/mbedtls/rsa_internal.h
@@ -0,0 +1,219 @@
+/**
+ * \file rsa_internal.h
+ *
+ * \brief Context-independent RSA helper functions
+ *
+ * Copyright (C) 2006-2017, ARM Limited, All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * This file is part of mbed TLS (https://tls.mbed.org)
+ *
+ *
+ * This file declares some RSA-related helper functions useful when
+ * implementing the RSA interface. They are public and provided in a
+ * separate compilation unit in order to make it easy for designers of
+ * alternative RSA implementations to use them in their code, as it is
+ * conceived that the functionality they provide will be necessary
+ * for most complete implementations.
+ *
+ * End-users of Mbed TLS not intending to re-implement the RSA functionality
+ * are not expected to get into the need of making use of these functions directly,
+ * but instead should be able to make do with the implementation of the RSA module.
+ *
+ * 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.
+ *
+ */
+
+#ifndef MBEDTLS_RSA_INTERNAL_H
+#define MBEDTLS_RSA_INTERNAL_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include "bignum.h"
+
+#if defined(MBEDTLS_RSA_C)
+
+#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 D RSA private exponent
+ * \param E RSA public 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 *D,
+ mbedtls_mpi const *E,
+ 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 = PQ
+ * - 1 < D, E < N
+ * - D and E are modular inverses modulo P-1 and Q-1
+ * - 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 );
+
+
+#endif /* MBEDTLS_RSA_C */
+
+#endif /* rsa_internal.h */