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mbedtls/library/bignum_internal.h
Manuel Pégourié-Gonnard c6b28b31ef Be explicit about modinv output range
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
2025-09-11 09:58:45 +02:00

123 lines
5.4 KiB
C

/**
* \file bignum_internal.h
*
* \brief Internal-only bignum public-key cryptosystem API.
*
* This file declares bignum-related functions that are to be used
* only from within the Mbed TLS library itself.
*
*/
/*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
*/
#ifndef MBEDTLS_BIGNUM_INTERNAL_H
#define MBEDTLS_BIGNUM_INTERNAL_H
/**
* \brief Perform a modular exponentiation: X = A^E mod N
*
* \warning This function is not constant time with respect to \p E (the exponent).
*
* \param X The destination MPI. This must point to an initialized MPI.
* This must not alias E or N.
* \param A The base of the exponentiation.
* This must point to an initialized MPI.
* \param E The exponent MPI. This must point to an initialized MPI.
* \param N The base for the modular reduction. This must point to an
* initialized MPI.
* \param prec_RR A helper MPI depending solely on \p N which can be used to
* speed-up multiple modular exponentiations for the same value
* of \p N. This may be \c NULL. If it is not \c NULL, it must
* point to an initialized MPI. If it hasn't been used after
* the call to mbedtls_mpi_init(), this function will compute
* the helper value and store it in \p prec_RR for reuse on
* subsequent calls to this function. Otherwise, the function
* will assume that \p prec_RR holds the helper value set by a
* previous call to mbedtls_mpi_exp_mod(), and reuse it.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \c N is negative or
* even, or if \c E is negative.
* \return Another negative error code on different kinds of failures.
*
*/
int mbedtls_mpi_exp_mod_unsafe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR);
/**
* \brief A wrapper around a constant time function to compute
* GCD(A, N) and/or A^-1 mod N if it exists.
*
* \warning Requires N to be odd, and 0 <= A <= N. Additionally, if
* I != NULL, requires N > 1.
* The wrapper part of this function is not constant time.
*
* \note A and N must not alias each other.
* When I == NULL (computing only the GCD), G can alias A or N.
* When I != NULL (computing the modular inverse), G or I can
* alias A, but neither of them can alias N (the modulus).
*
* \param[out] G The GCD of \p A and \p N.
* This may be NULL, to only compute I.
* \param[out] I The inverse of \p A modulo \p N if it exists (that is,
* if \p G above is 1 on exit), in the range [1, \p N);
* indeterminate otherwise.
* This may be NULL, to only compute G.
* \param[in] A The 1st operand of GCD and number to invert.
* This value must be less than or equal to \p N.
* \param[in] N The 2nd operand of GCD and modulus for inversion.
* Must be odd or the results are indeterminate.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if preconditions were not
* met.
*/
int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
mbedtls_mpi *I,
const mbedtls_mpi *A,
const mbedtls_mpi *N);
/**
* \brief Modular inverse: X = A^-1 mod N with N odd
*
* \param[out] X The inverse of \p A modulo \p N in the range [1, \p N)
* on success; indeterminate otherwise.
* \param[in] A The number to invert.
* \param[in] N The modulus. Must be odd and greater than 1.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if preconditions were not
* met.
* \return #MBEDTLS_ERR_MPI_NOT_ACCEPTABLE if A is not invertible mod N.
*/
int mbedtls_mpi_inv_mod_odd(mbedtls_mpi *X,
const mbedtls_mpi *A,
const mbedtls_mpi *N);
/**
* \brief Modular inverse: X = A^-1 mod N with N even,
* A odd and 1 < A < N.
*
* \param[out] X The inverse of \p A modulo \p N in the range [1, \p N)
* on success; indeterminate otherwise.
* \param[in] A The number to invert. Must be odd, greated than 1
* and less than \p N.
* \param[in] N The modulus. Must be even and greater than 1.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if preconditions were not
* met.
* \return #MBEDTLS_ERR_MPI_NOT_ACCEPTABLE if A is not invertible mod N.
*/
int mbedtls_mpi_inv_mod_even_in_range(mbedtls_mpi *X,
mbedtls_mpi const *A,
mbedtls_mpi const *N);
#endif /* bignum_internal.h */