mbedtls/library/bignum_core.h
Tom Cosgrove 82f131063a Update documentation following review comment
Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
2022-10-25 16:29:58 +01:00

437 lines
19 KiB
C

/**
* Core bignum functions
*
* This interface should only be used by the legacy bignum module (bignum.h)
* and the modular bignum modules (bignum_mod.c, bignum_mod_raw.c). All other
* modules should use the high-level modular bignum interface (bignum_mod.h)
* or the legacy bignum interface (bignum.h).
*
* This module is about processing non-negative integers with a fixed upper
* bound that's of the form 2^n-1 where n is a multiple of #biL.
* These can be thought of integers written in base 2^#biL with a fixed
* number of digits. Digits in this base are called *limbs*.
* Many operations treat these numbers as the principal representation of
* a number modulo 2^n or a smaller bound.
*
* The functions in this module obey the following conventions unless
* explicitly indicated otherwise:
*
* - **Overflow**: some functions indicate overflow from the range
* [0, 2^n-1] by returning carry parameters, while others operate
* modulo and so cannot overflow. This should be clear from the function
* documentation.
* - **Bignum parameters**: Bignums are passed as pointers to an array of
* limbs. A limb has the type #mbedtls_mpi_uint. Unless otherwise specified:
* - Bignum parameters called \p A, \p B, ... are inputs, and are
* not modified by the function.
* - For operations modulo some number, the modulus is called \p N
* and is input-only.
* - Bignum parameters called \p X, \p Y are outputs or input-output.
* The initial content of output-only parameters is ignored.
* - Some functions use different names that reflect traditional
* naming of operands of certain operations (e.g.
* divisor/dividend/quotient/remainder).
* - \p T is a temporary storage area. The initial content of such
* parameter is ignored and the final content is unspecified.
* - **Bignum sizes**: bignum sizes are always expressed in limbs.
* Most functions work on bignums of a given size and take a single
* \p limbs parameter that applies to all parameters that are limb arrays.
* All bignum sizes must be at least 1 and must be significantly less than
* #SIZE_MAX. The behavior if a size is 0 is undefined. The behavior if the
* total size of all parameters overflows #SIZE_MAX is undefined.
* - **Parameter ordering**: for bignum parameters, outputs come before inputs.
* Temporaries come last.
* - **Aliasing**: in general, output bignums may be aliased to one or more
* inputs. As an exception, parameters that are documented as a modulus value
* may not be aliased to an output. Outputs may not be aliased to one another.
* Temporaries may not be aliased to any other parameter.
* - **Overlap**: apart from aliasing of limb array pointers (where two
* arguments are equal pointers), overlap is not supported and may result
* in undefined behavior.
* - **Error handling**: This is a low-level module. Functions generally do not
* try to protect against invalid arguments such as nonsensical sizes or
* null pointers. Note that some functions that operate on bignums of
* different sizes have constraints about their size, and violating those
* constraints may lead to buffer overflows.
* - **Modular representatives**: functions that operate modulo \p N expect
* all modular inputs to be in the range [0, \p N - 1] and guarantee outputs
* in the range [0, \p N - 1]. If an input is out of range, outputs are
* fully unspecified, though bignum values out of range should not cause
* buffer overflows (beware that this is not extensively tested).
*/
/*
* Copyright The Mbed TLS Contributors
* 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.
*/
#ifndef MBEDTLS_BIGNUM_CORE_H
#define MBEDTLS_BIGNUM_CORE_H
#include "common.h"
#if defined(MBEDTLS_BIGNUM_C)
#include "mbedtls/bignum.h"
#endif
#define ciL ( sizeof(mbedtls_mpi_uint) ) /** chars in limb */
#define biL ( ciL << 3 ) /** bits in limb */
#define biH ( ciL << 2 ) /** half limb size */
/*
* Convert between bits/chars and number of limbs
* Divide first in order to avoid potential overflows
*/
#define BITS_TO_LIMBS(i) ( (i) / biL + ( (i) % biL != 0 ) )
#define CHARS_TO_LIMBS(i) ( (i) / ciL + ( (i) % ciL != 0 ) )
/* Get a specific byte, without range checks. */
#define GET_BYTE( X, i ) \
( ( (X)[(i) / ciL] >> ( ( (i) % ciL ) * 8 ) ) & 0xff )
/** Count leading zero bits in a given integer.
*
* \param a Integer to count leading zero bits.
*
* \return The number of leading zero bits in \p a.
*/
size_t mbedtls_mpi_core_clz( mbedtls_mpi_uint a );
/** Return the minimum number of bits required to represent the value held
* in the MPI.
*
* \note This function returns 0 if all the limbs of \p A are 0.
*
* \param[in] A The address of the MPI.
* \param A_limbs The number of limbs of \p A.
*
* \return The number of bits in \p A.
*/
size_t mbedtls_mpi_core_bitlen( const mbedtls_mpi_uint *A, size_t A_limbs );
/** Convert a big-endian byte array aligned to the size of mbedtls_mpi_uint
* into the storage form used by mbedtls_mpi.
*
* \param[in,out] A The address of the MPI.
* \param A_limbs The number of limbs of \p A.
*/
void mbedtls_mpi_core_bigendian_to_host( mbedtls_mpi_uint *A,
size_t A_limbs );
/**
* \brief Perform a safe conditional copy of an MPI which doesn't reveal
* whether assignment was done or not.
*
* \param[out] X The address of the destination MPI.
* This must be initialized. Must have enough limbs to
* store the full value of \p A.
* \param[in] A The address of the source MPI. This must be initialized.
* \param limbs The number of limbs of \p A.
* \param assign The condition deciding whether to perform the
* assignment or not. Must be either 0 or 1:
* * \c 1: Perform the assignment `X = A`.
* * \c 0: Keep the original value of \p X.
*
* \note This function avoids leaking any information about whether
* the assignment was done or not.
*
* \warning If \p assign is neither 0 nor 1, the result of this function
* is indeterminate, and the resulting value in \p X might be
* neither its original value nor the value in \p A.
*/
void mbedtls_mpi_core_cond_assign( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
size_t limbs,
unsigned char assign );
/**
* \brief Perform a safe conditional swap of two MPIs which doesn't reveal
* whether the swap was done or not.
*
* \param[in,out] X The address of the first MPI.
* This must be initialized.
* \param[in,out] Y The address of the second MPI.
* This must be initialized.
* \param limbs The number of limbs of \p X and \p Y.
* \param swap The condition deciding whether to perform
* the swap or not. Must be either 0 or 1:
* * \c 1: Swap the values of \p X and \p Y.
* * \c 0: Keep the original values of \p X and \p Y.
*
* \note This function avoids leaking any information about whether
* the swap was done or not.
*
* \warning If \p swap is neither 0 nor 1, the result of this function
* is indeterminate, and both \p X and \p Y might end up with
* values different to either of the original ones.
*/
void mbedtls_mpi_core_cond_swap( mbedtls_mpi_uint *X,
mbedtls_mpi_uint *Y,
size_t limbs,
unsigned char swap );
/** Import X from unsigned binary data, little-endian.
*
* The MPI needs to have enough limbs to store the full value (including any
* most significant zero bytes in the input).
*
* \param[out] X The address of the MPI.
* \param X_limbs The number of limbs of \p X.
* \param[in] input The input buffer to import from.
* \param input_length The length bytes of \p input.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
* large enough to hold the value in \p input.
*/
int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
size_t X_limbs,
const unsigned char *input,
size_t input_length );
/** Import X from unsigned binary data, big-endian.
*
* The MPI needs to have enough limbs to store the full value (including any
* most significant zero bytes in the input).
*
* \param[out] X The address of the MPI.
* May only be #NULL if \X_limbs is 0 and \p input_length
* is 0.
* \param X_limbs The number of limbs of \p X.
* \param[in] input The input buffer to import from.
* May only be #NULL if \p input_length is 0.
* \param input_length The length in bytes of \p input.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
* large enough to hold the value in \p input.
*/
int mbedtls_mpi_core_read_be( mbedtls_mpi_uint *X,
size_t X_limbs,
const unsigned char *input,
size_t input_length );
/** Export A into unsigned binary data, little-endian.
*
* \note If \p output is shorter than \p A the export is still successful if the
* value held in \p A fits in the buffer (that is, if enough of the most
* significant bytes of \p A are 0).
*
* \param[in] A The address of the MPI.
* \param A_limbs The number of limbs of \p A.
* \param[out] output The output buffer to export to.
* \param output_length The length in bytes of \p output.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p output isn't
* large enough to hold the value of \p A.
*/
int mbedtls_mpi_core_write_le( const mbedtls_mpi_uint *A,
size_t A_limbs,
unsigned char *output,
size_t output_length );
/** Export A into unsigned binary data, big-endian.
*
* \note If \p output is shorter than \p A the export is still successful if the
* value held in \p A fits in the buffer (that is, if enough of the most
* significant bytes of \p A are 0).
*
* \param[in] A The address of the MPI.
* \param A_limbs The number of limbs of \p A.
* \param[out] output The output buffer to export to.
* \param output_length The length in bytes of \p output.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p output isn't
* large enough to hold the value of \p A.
*/
int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *A,
size_t A_limbs,
unsigned char *output,
size_t output_length );
/** \brief Shift an MPI right in place by a number of bits.
*
* Shifting by more bits than there are bit positions
* in \p X is valid and results in setting \p X to 0.
*
* This function's execution time depends on the value
* of \p count (and of course \p limbs).
*
* \param[in,out] X The number to shift.
* \param limbs The number of limbs of \p X. This must be at least 1.
* \param count The number of bits to shift by.
*/
void mbedtls_mpi_core_shift_r( mbedtls_mpi_uint *X, size_t limbs,
size_t count );
/**
* \brief Add two fixed-size large unsigned integers, returning the carry.
*
* Calculates `A + B` where `A` and `B` have the same size.
*
* This function operates modulo `2^(biL*limbs)` and returns the carry
* (1 if there was a wraparound, and 0 otherwise).
*
* \p X may be aliased to \p A or \p B.
*
* \param[out] X The result of the addition.
* \param[in] A Little-endian presentation of the left operand.
* \param[in] B Little-endian presentation of the right operand.
* \param limbs Number of limbs of \p X, \p A and \p B.
*
* \return 1 if `A + B >= 2^(biL*limbs)`, 0 otherwise.
*/
mbedtls_mpi_uint mbedtls_mpi_core_add( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *B,
size_t limbs );
/**
* \brief Conditional addition of two fixed-size large unsigned integers,
* returning the carry.
*
* Functionally equivalent to
*
* ```
* if( cond )
* X += A;
* return carry;
* ```
*
* This function operates modulo `2^(biL*limbs)`.
*
* \param[in,out] X The pointer to the (little-endian) array
* representing the bignum to accumulate onto.
* \param[in] A The pointer to the (little-endian) array
* representing the bignum to conditionally add
* to \p X. This may be aliased to \p X but may not
* overlap otherwise.
* \param limbs Number of limbs of \p X and \p A.
* \param cond Condition bit dictating whether addition should
* happen or not. This must be \c 0 or \c 1.
*
* \warning If \p cond is neither 0 nor 1, the result of this function
* is unspecified, and the resulting value in \p X might be
* neither its original value nor \p X + \p A.
*
* \return 1 if `X + cond * A >= 2^(biL*limbs)`, 0 otherwise.
*/
mbedtls_mpi_uint mbedtls_mpi_core_add_if( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
size_t limbs,
unsigned cond );
/**
* \brief Subtract two fixed-size large unsigned integers, returning the borrow.
*
* Calculate `A - B` where \p A and \p B have the same size.
* This function operates modulo `2^(biL*limbs)` and returns the carry
* (1 if there was a wraparound, i.e. if `A < B`, and 0 otherwise).
*
* \p X may be aliased to \p A or \p B, or even both, but may not overlap
* either otherwise.
*
* \param[out] X The result of the subtraction.
* \param[in] A Little-endian presentation of left operand.
* \param[in] B Little-endian presentation of right operand.
* \param limbs Number of limbs of \p X, \p A and \p B.
*
* \return 1 if `A < B`.
* 0 if `A >= B`.
*/
mbedtls_mpi_uint mbedtls_mpi_core_sub( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *B,
size_t limbs );
/**
* \brief Perform a fixed-size multiply accumulate operation: X += b * A
*
* \p X may be aliased to \p A (when \p X_limbs == \p A_limbs), but may not
* otherwise overlap.
*
* This function operates modulo `2^(biL*X_limbs)`.
*
* \param[in,out] X The pointer to the (little-endian) array
* representing the bignum to accumulate onto.
* \param X_limbs The number of limbs of \p X. This must be
* at least \p A_limbs.
* \param[in] A The pointer to the (little-endian) array
* representing the bignum to multiply with.
* This may be aliased to \p X but may not overlap
* otherwise.
* \param A_limbs The number of limbs of \p A.
* \param b X scalar to multiply with.
*
* \return The carry at the end of the operation.
*/
mbedtls_mpi_uint mbedtls_mpi_core_mla( mbedtls_mpi_uint *X, size_t X_limbs,
const mbedtls_mpi_uint *A, size_t A_limbs,
mbedtls_mpi_uint b );
/**
* \brief Calculate initialisation value for fast Montgomery modular
* multiplication
*
* \param[in] N Little-endian presentation of the modulus. This must have
* at least one limb.
*
* \return The initialisation value for fast Montgomery modular multiplication
*/
mbedtls_mpi_uint mbedtls_mpi_core_montmul_init( const mbedtls_mpi_uint *N );
/**
* \brief Montgomery multiplication: X = A * B * R^-1 mod N (HAC 14.36)
*
* \p A and \p B must be in canonical form. That is, < \p N.
*
* \p X may be aliased to \p A or \p N, or even \p B (if \p AN_limbs ==
* \p B_limbs) but may not overlap any parameters otherwise.
*
* \p A and \p B may alias each other, if \p AN_limbs == \p B_limbs. They may
* not alias \p N (since they must be in canonical form, they cannot == \p N).
*
* \param[out] X The destination MPI, as a little-endian array of
* length \p AN_limbs.
* On successful completion, X contains the result of
* the multiplication `A * B * R^-1` mod N where
* `R = 2^(biL*AN_limbs)`.
* \param[in] A Little-endian presentation of first operand.
* Must have the same number of limbs as \p N.
* \param[in] B Little-endian presentation of second operand.
* \param[in] B_limbs The number of limbs in \p B.
* Must be <= \p AN_limbs.
* \param[in] N Little-endian presentation of the modulus.
* This must be odd, and have exactly the same number
* of limbs as \p A.
* It may alias \p X, but must not alias or otherwise
* overlap any of the other parameters.
* \param[in] AN_limbs The number of limbs in \p X, \p A and \p N.
* \param mm The Montgomery constant for \p N: -N^-1 mod 2^biL.
* This can be calculated by `mbedtls_mpi_core_montmul_init()`.
* \param[in,out] T Temporary storage of size at least 2*AN_limbs+1 limbs.
* Its initial content is unused and
* its final content is indeterminate.
* It must not alias or otherwise overlap any of the
* other parameters.
*/
void mbedtls_mpi_core_montmul( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *B, size_t B_limbs,
const mbedtls_mpi_uint *N, size_t AN_limbs,
mbedtls_mpi_uint mm, mbedtls_mpi_uint *T );
#endif /* MBEDTLS_BIGNUM_CORE_H */