| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new,
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| 6 | BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using
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| 7 | reciprocal
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| 8 |
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| 9 | =head1 SYNOPSIS
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| 10 |
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| 11 | #include <openssl/bn.h>
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| 12 |
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| 13 | BN_RECP_CTX *BN_RECP_CTX_new(void);
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| 14 | void BN_RECP_CTX_free(BN_RECP_CTX *recp);
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| 15 |
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| 16 | int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
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| 17 |
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| 18 | int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, BN_RECP_CTX *recp,
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| 19 | BN_CTX *ctx);
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| 20 |
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| 21 | int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
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| 22 | BN_RECP_CTX *recp, BN_CTX *ctx);
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| 23 |
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| 24 | =head1 DESCRIPTION
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| 25 |
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| 26 | BN_mod_mul_reciprocal() can be used to perform an efficient
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| 27 | L<BN_mod_mul(3)> operation when the operation will be performed
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| 28 | repeatedly with the same modulus. It computes B<r>=(B<a>*B<b>)%B<m>
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| 29 | using B<recp>=1/B<m>, which is set as described below. B<ctx> is a
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| 30 | previously allocated B<BN_CTX> used for temporary variables.
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| 31 |
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| 32 | BN_RECP_CTX_new() allocates and initializes a B<BN_RECP> structure.
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| 33 |
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| 34 | BN_RECP_CTX_free() frees the components of the B<BN_RECP>, and, if it
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| 35 | was created by BN_RECP_CTX_new(), also the structure itself.
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| 36 | If B<recp> is NULL, nothing is done.
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| 37 |
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| 38 | BN_RECP_CTX_set() stores B<m> in B<recp> and sets it up for computing
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| 39 | 1/B<m> and shifting it left by BN_num_bits(B<m>)+1 to make it an
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| 40 | integer. The result and the number of bits it was shifted left will
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| 41 | later be stored in B<recp>.
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| 42 |
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| 43 | BN_div_recp() divides B<a> by B<m> using B<recp>. It places the quotient
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| 44 | in B<dv> and the remainder in B<rem>.
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| 45 |
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| 46 | The B<BN_RECP_CTX> structure cannot be shared between threads.
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| 47 |
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| 48 | =head1 RETURN VALUES
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| 49 |
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| 50 | BN_RECP_CTX_new() returns the newly allocated B<BN_RECP_CTX>, and NULL
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| 51 | on error.
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| 52 |
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| 53 | BN_RECP_CTX_free() has no return value.
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| 54 |
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| 55 | For the other functions, 1 is returned for success, 0 on error.
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| 56 | The error codes can be obtained by L<ERR_get_error(3)>.
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| 57 |
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| 58 | =head1 SEE ALSO
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| 59 |
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| 60 | L<ERR_get_error(3)>, L<BN_add(3)>,
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| 61 | L<BN_CTX_new(3)>
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| 62 |
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| 63 | =head1 HISTORY
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| 64 |
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| 65 | BN_RECP_CTX_init() was removed in OpenSSL 1.1.0
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| 66 |
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| 67 | =head1 COPYRIGHT
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| 68 |
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| 69 | Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 70 |
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| 71 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 72 | this file except in compliance with the License. You can obtain a copy
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| 73 | in the file LICENSE in the source distribution or at
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| 74 | L<https://www.openssl.org/source/license.html>.
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| 75 |
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| 76 | =cut
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