225 lines
6.6 KiB
Groff
225 lines
6.6 KiB
Groff
.\" $NetBSD: BN_mod_mul_reciprocal.3,v 1.5 2001/04/12 10:45:36 itojun Exp $
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.\" Thu Apr 12 19:26:48 2001
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.\" ======================================================================
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.\"
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.IX Title "BN_mod_mul_reciprocal 3"
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.TH BN_mod_mul_reciprocal 3 "0.9.6a" "2001-04-12" "OpenSSL"
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.UC
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.SH "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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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bn.h>
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.Ve
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.Vb 3
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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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.Ve
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.Vb 1
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\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
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.Ve
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.Vb 2
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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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.Ve
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.Vb 2
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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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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
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BN_mod_mul(3) operation when the operation will be performed
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repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
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using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
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previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
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.PP
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\&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure.
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\&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR.
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.PP
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\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
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was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
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.PP
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\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
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1/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+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 \fBrecp\fR.
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.PP
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\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
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in \fBdv\fR and the remainder in \fBrem\fR.
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.PP
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The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
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.PP
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.Vb 8
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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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.Ve
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It cannot be shared between threads.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0
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on error.
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.PP
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\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
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.PP
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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 ERR_get_error(3).
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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openssl_bn(3), openssl_err(3), BN_add(3),
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BN_CTX_new(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function
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\&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
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arguments were different.
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