mirror of https://github.com/openssl/openssl.git
82 lines
2.3 KiB
Plaintext
82 lines
2.3 KiB
Plaintext
=pod
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=head1 NAME
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BN_mod_mul_reciprocal, BN_RECP_CTX_new, BN_RECP_CTX_init,
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BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using
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reciprocal
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=head1 SYNOPSIS
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#include <openssl/bn.h>
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BN_RECP_CTX *BN_RECP_CTX_new(void);
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void BN_RECP_CTX_init(BN_RECP_CTX *recp);
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void BN_RECP_CTX_free(BN_RECP_CTX *recp);
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int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
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int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
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BN_CTX *ctx);
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int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
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BN_RECP_CTX *recp, BN_CTX *ctx);
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=head1 DESCRIPTION
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BN_mod_mul_reciprocal() can be used to perform an efficient
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L<BN_mod_mul(3)|BN_mod_mul(3)> operation when the operation will be performed
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repeatedly with the same modulus. It computes B<r>=(B<a>*B<b>)%B<m>
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using B<recp>=1/B<m>, which is set as described below. B<ctx> is a
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previously allocated B<BN_CTX> used for temporary variables.
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BN_RECP_CTX_new() allocates and initializes a B<BN_RECP> structure.
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BN_RECP_CTX_init() initializes an existing uninitialized B<BN_RECP>.
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BN_RECP_CTX_free() frees the components of the B<BN_RECP>, and, if it
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was created by BN_RECP_CTX_new(), also the structure itself.
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BN_RECP_CTX_set() stores B<m> in B<recp> and sets it up for computing
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1/B<m> and shifting it left by BN_num_bits(B<m>)+1 to make it an
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integer. The result and the number of bits it was shifted left will
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later be stored in B<recp>.
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BN_div_recp() divides B<a> by B<m> using B<recp>. It places the quotient
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in B<dv> and the remainder in B<rem>.
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The B<BN_RECP_CTX> structure is defined as follows:
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typedef struct bn_recp_ctx_st
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{
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BIGNUM N; /* the divisor */
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BIGNUM Nr; /* the reciprocal */
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int num_bits;
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int shift;
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int flags;
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} BN_RECP_CTX;
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It cannot be shared between threads.
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=head1 RETURN VALUES
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BN_RECP_CTX_new() returns the newly allocated B<BN_RECP_CTX>, and NULL
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on error.
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BN_RECP_CTX_init() and BN_RECP_CTX_free() have no return values.
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For the other functions, 1 is returned for success, 0 on error.
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The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
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=head1 SEE ALSO
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L<bn(3)|bn(3)>, L<err(3)|err(3)>, L<BN_add(3)|BN_add(3)>,
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L<BN_CTX_new(3)|BN_CTX_new(3)>
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=head1 HISTORY
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B<BN_RECP_CTX> was added in SSLeay 0.9.0. Before that, the function
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BN_reciprocal() was used instead, and the BN_mod_mul_reciprocal()
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arguments were different.
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=cut
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