126 lines
3.5 KiB
Groff
126 lines
3.5 KiB
Groff
.\" $OpenBSD: BN_mod_inverse.3,v 1.13 2023/10/21 13:53:43 schwarze Exp $
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.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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.\"
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.\" This file was written by Ulf Moeller <ulf@openssl.org>.
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.\" Copyright (c) 2000 The OpenSSL Project. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" 3. All advertising materials mentioning features or use of this
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.\" software must display the following acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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.\"
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.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
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.\" endorse or promote products derived from this software without
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.\" prior written permission. For written permission, please contact
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.\" openssl-core@openssl.org.
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.\"
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.\" 5. Products derived from this software may not be called "OpenSSL"
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.\" nor may "OpenSSL" appear in their names without prior written
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.\" permission of the OpenSSL Project.
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.\"
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.\" 6. Redistributions of any form whatsoever must retain the following
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.\" acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
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.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
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.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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.\" OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: October 21 2023 $
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.Dt BN_MOD_INVERSE 3
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.Os
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.Sh NAME
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.Nm BN_mod_inverse
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.Nd compute inverse modulo m
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.Sh SYNOPSIS
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.In openssl/bn.h
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.Ft BIGNUM *
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.Fo BN_mod_inverse
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.Fa "BIGNUM *r"
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.Fa "const BIGNUM *a"
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.Fa "const BIGNUM *m"
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.Fa "BN_CTX *ctx"
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.Fc
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.Sh DESCRIPTION
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.Fn BN_mod_inverse
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computes the inverse of
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.Fa a
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modulo
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.Fa m
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and places the result in
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.Fa r ,
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so that
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.Fa r
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satisfies
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.Li a * r == 1 (mod m) .
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If
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.Fa r
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is
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.Dv NULL ,
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a new
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.Vt BIGNUM
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is allocated.
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.Pp
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If the flag
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.Dv BN_FLG_CONSTTIME
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is set on
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.Fa a
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or
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.Fa m ,
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it operates in constant time.
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.Pp
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.Fa ctx
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is a previously allocated
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.Vt BN_CTX
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used for temporary variables.
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.Fa r
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may be the same
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.Vt BIGNUM
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as
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.Fa a
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or
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.Fa m .
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.Sh RETURN VALUES
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.Fn BN_mod_inverse
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returns the
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.Vt BIGNUM
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containing the inverse, or
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.Dv NULL
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on error.
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The error codes can be obtained by
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.Xr ERR_get_error 3 .
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.Sh SEE ALSO
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.Xr BN_add 3 ,
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.Xr BN_new 3 ,
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.Xr BN_set_flags 3
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.Sh HISTORY
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.Fn BN_mod_inverse
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first appeared in SSLeay 0.5.1 and has been available since
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.Ox 2.4 .
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.Pp
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The
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.Fa r
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argument was added in SSLeay 0.9.1 and
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.Ox 2.6 .
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