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81 lines
2.4 KiB
81 lines
2.4 KiB
=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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