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