Source code
Revision control
Copy as Markdown
Other Tools
/*
* Classic McEliece Field Ordering Generation
* (C) 2023 Jack Lloyd
* 2023,2024 Fabian Albert, Amos Treiber - Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
**/
#ifndef BOTAN_CMCE_FIELD_ORDERING_H_
#define BOTAN_CMCE_FIELD_ORDERING_H_
#include <botan/internal/cmce_parameters.h>
#include <botan/internal/cmce_types.h>
#include <numeric>
namespace Botan {
/**
* @brief Represents a field ordering for the Classic McEliece cryptosystem.
*
* Field ordering corresponds to the permutation pi defining the alpha sequence in
* the Classic McEliece specification (see Classic McEliece ISO Sec. 8.2.).
*/
class BOTAN_TEST_API Classic_McEliece_Field_Ordering {
public:
/**
* @brief Creates a field ordering from a random bit sequence. Corresponds to
* the algorithm described in Classic McEliece ISO Sec. 8.2.
*
* @param params The McEliece parameters.
* @param random_bits The random bit sequence.
* @return The field ordering.
*/
static std::optional<Classic_McEliece_Field_Ordering> create_field_ordering(
const Classic_McEliece_Parameters& params, StrongSpan<const CmceOrderingBits> random_bits);
/**
* @brief Create the field ordering from the control bits of a benes network.
*
* @param params The McEliece parameters.
* @param control_bits The control bits of the benes network.
* @return The field ordering.
*/
static Classic_McEliece_Field_Ordering create_from_control_bits(const Classic_McEliece_Parameters& params,
const secure_bitvector& control_bits);
/**
* @brief Returns the field ordering as a vector of all alphas from alpha_0 to alpha_{n-1}.
*
* @param n The number of alphas to return.
* @return the vector of n alphas.
*/
std::vector<Classic_McEliece_GF> alphas(size_t n) const;
/**
* @brief Generates the control bits of the benes network corresponding to the field ordering.
*
* @return the control bits.
*/
secure_bitvector alphas_control_bits() const;
/**
* @brief The pi values representing the field ordering.
*
* @return pi values.
*/
CmcePermutation& pi_ref() { return m_pi; }
/**
* @brief The pi values representing the field ordering.
*
* @return pi values.
*/
const CmcePermutation& pi_ref() const { return m_pi; }
/**
* @brief Constant time comparison of two field orderings.
*
* @param other The other field ordering.
* @return Mask of equality value
*/
CT::Mask<uint16_t> ct_is_equal(const Classic_McEliece_Field_Ordering& other) const {
BOTAN_ARG_CHECK(other.pi_ref().size() == pi_ref().size(), "Field orderings must have the same size");
return CT::is_equal(pi_ref().data(), other.pi_ref().data(), pi_ref().size());
}
/**
* @brief Permute the field ordering with the given pivots.
*
* For example: If the pivot vector is 10101, the first, third and fifth element of the field ordering
* are permuted to positions 0, 1 and 2, respectively. The remaining elements are put at the end.
*
* The permutation is done for the elements from position m*t - mu,..., m*t + mu (excl.).
* This function implements Classic McEliece ISO Sec. 7.2.3 Steps 4-5.
*
* @param params The McEliece parameters.
* @param pivots The pivot vector.
*/
void permute_with_pivots(const Classic_McEliece_Parameters& params, const CmceColumnSelection& pivots);
void _const_time_poison() const { CT::poison(m_pi); }
void _const_time_unpoison() const { CT::unpoison(m_pi); }
private:
Classic_McEliece_Field_Ordering(CmcePermutation pi, CmceGfMod poly_f) : m_pi(std::move(pi)), m_poly_f(poly_f) {}
private:
CmcePermutation m_pi;
CmceGfMod m_poly_f;
};
} // namespace Botan
#endif