66 lines
2.6 KiB
Plaintext
66 lines
2.6 KiB
Plaintext
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=pod
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=head1 NAME
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BN_mod_exp_mont, BN_mod_exp_mont_consttime, BN_mod_exp_mont_consttime_x2 -
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Montgomery exponentiation
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=head1 SYNOPSIS
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#include <openssl/bn.h>
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int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont);
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int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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const BIGNUM *m, BN_CTX *ctx,
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BN_MONT_CTX *in_mont);
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int BN_mod_exp_mont_consttime_x2(BIGNUM *rr1, const BIGNUM *a1,
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const BIGNUM *p1, const BIGNUM *m1,
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BN_MONT_CTX *in_mont1, BIGNUM *rr2,
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const BIGNUM *a2, const BIGNUM *p2,
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const BIGNUM *m2, BN_MONT_CTX *in_mont2,
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BN_CTX *ctx);
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=head1 DESCRIPTION
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BN_mod_exp_mont() computes I<a> to the I<p>-th power modulo I<m> (C<rr=a^p % m>)
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using Montgomery multiplication. I<in_mont> is a Montgomery context and can be
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NULL. In the case I<in_mont> is NULL, it will be initialized within the
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function, so you can save time on initialization if you provide it in advance.
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BN_mod_exp_mont_consttime() computes I<a> to the I<p>-th power modulo I<m>
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(C<rr=a^p % m>) using Montgomery multiplication. It is a variant of
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L<BN_mod_exp_mont(3)> that uses fixed windows and the special precomputation
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memory layout to limit data-dependency to a minimum to protect secret exponents.
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It is called automatically when L<BN_mod_exp_mont(3)> is called with parameters
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I<a>, I<p>, I<m>, any of which have B<BN_FLG_CONSTTIME> flag.
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BN_mod_exp_mont_consttime_x2() computes two independent exponentiations I<a1> to
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the I<p1>-th power modulo I<m1> (C<rr1=a1^p1 % m1>) and I<a2> to the I<p2>-th
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power modulo I<m2> (C<rr2=a2^p2 % m2>) using Montgomery multiplication. For some
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fixed and equal modulus sizes I<m1> and I<m2> it uses optimizations that allow
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to speedup two exponentiations. In all other cases the function reduces to two
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calls of L<BN_mod_exp_mont_consttime(3)>.
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=head1 RETURN VALUES
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For all 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)>.
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=head1 SEE ALSO
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L<ERR_get_error(3)>, L<BN_mod_exp_mont(3)>
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=head1 COPYRIGHT
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Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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