6859cf7459
manual when the specific function is refered to in the current manual text. This correction was originally introduced in OpenBSD's tracking of OpenSSL.
81 lines
2.4 KiB
Text
81 lines
2.4 KiB
Text
=pod
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=head1 NAME
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BN_mod_mul_reciprocal, BN_div_recp, 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_get_error(3)|ERR_get_error(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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