148 lines
5.2 KiB
Groff
148 lines
5.2 KiB
Groff
.\" $OpenBSD: BN_swap.3,v 1.6 2021/12/19 22:06:35 schwarze Exp $
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.\" full merge up to: OpenSSL 61f805c1 Jan 16 01:01:46 2018 +0800
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.\"
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.\" This file is a derived work.
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.\" The changes are covered by the following Copyright and license:
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.\"
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.\" Copyright (c) 2021 Ingo Schwarze <schwarze@openbsd.org>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" The original file was written by Bodo Moeller <bodo@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: December 19 2021 $
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.Dt BN_SWAP 3
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.Os
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.Sh NAME
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.Nm BN_swap ,
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.Nm BN_consttime_swap
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.Nd exchange BIGNUMs
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.Sh SYNOPSIS
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.In openssl/bn.h
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.Ft void
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.Fo BN_swap
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.Fa "BIGNUM *a"
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.Fa "BIGNUM *b"
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.Fc
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.Ft void
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.Fo BN_consttime_swap
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.Fa "BN_ULONG condition"
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.Fa "BIGNUM *a"
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.Fa "BIGNUM *b"
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.Fa "int nwords"
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.Fc
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.Sh DESCRIPTION
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.Fn BN_swap
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and
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.Fn BN_consttime_swap
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exchange the values of
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.Fa a
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and
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.Fa b .
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.Pp
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.Fn BN_swap
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implements this by exchanging the pointers to the data buffers of
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.Fa a
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and
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.Fa b
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and also exchanging the values of the
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.Dv BN_FLG_STATIC_DATA
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bits.
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Consequently, the operation is fast and execution time does not depend
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on any properties of the two numbers.
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However, execution time obviously differs between swapping (by calling
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this function) and not swapping (by not calling this function).
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.Pp
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.Fn BN_consttime_swap
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only performs the exchange if the
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.Fa condition
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is non-zero; otherwise, it has no effect.
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It implements the exchange by exchanging the contents of the data
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buffers rather than the pointers to the data buffers.
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This is slower, but implemented in such a way that the execution time
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is not only independent of the properties of the two numbers, but also
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independent of the
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.Fa condition
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argument, i.e. the same for swapping or not swapping.
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Execution time does however grow in an approximately linear manner with the
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.Fa nwords
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argument.
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.Pp
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.Fn BN_consttime_swap
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calls
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.Xr abort 3
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if at least one of
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.Fa a
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or
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.Fa b
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has fewer than
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.Fa nwords
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data words allocated or more than
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.Fa nwords
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data words are currently in use in at least one of them.
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.Sh SEE ALSO
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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_swap
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first appeared in OpenSSL 0.9.7 and has been available since
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.Ox 3.2 .
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.Pp
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.Fn BN_consttime_swap
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first appeared in OpenSSL 1.0.1g and has been available since
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.Ox 5.6 .
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