/* * Low level API for Daan Sprenkels' Shamir secret sharing library * Copyright (c) 2017 Daan Sprenkels <hello@dsprenkels.com> * Copyright (c) 2019 SatoshiLabs * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included * in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * * Usage of this API is hazardous and is only reserved for beings with a * good understanding of the Shamir secret sharing scheme and who know how * crypto code is implemented. If you are unsure about this, use the * intermediate level API. You have been warned! */ #ifndef __SHAMIR_H__ #define __SHAMIR_H__ #include <stdbool.h> #include <stddef.h> #include <stdint.h> #define SHAMIR_MAX_LEN 32 /* * Computes f(x) given the Shamir shares (x_1, f(x_1)), ... , (x_m, f(x_m)). * The x coordinates of the shares must be pairwise distinct. Returns true on * success, otherwise false. * result: Array of length len where the evaluations of the polynomials in x * will be written. * result_index: The x coordinate of the result. * share_indices: Points to the array of integers x_1, ... , x_m. * share_values: Points to the array of y_1, ... , y_m, where each y_i is an * array of bytes of length len representing the evaluations of the * polynomials in x_i. * share_count: The number of shares m. * len: The length of the result array and of each of the y_1, ... , y_m arrays. * * The number of shares used to compute the result may be larger than the * required threshold. * * This function does *not* do *any* checking for integrity. If any of the * shares are not original, this will result in an invalid restored value. * All values written to `result` should be treated as secret. Even if some of * the shares that were provided as input were incorrect, the result *still* * allows an attacker to gain information about the correct result. * * This function treats `shares_values`, `share_indices` and `result` as secret * values. `share_count` is treated as a public value (for performance reasons). */ bool shamir_interpolate(uint8_t *result, uint8_t result_index, const uint8_t *share_indices, const uint8_t **share_values, uint8_t share_count, size_t len); #endif /* __SHAMIR_H__ */