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Title "BN_MOD_MUL_MONTGOMERY 3ossl"
BN_MOD_MUL_MONTGOMERY 3ossl "2023-09-19" "3.0.11" "OpenSSL"
For nroff, turn off justification. Always turn off hyphenation; it makes
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"NAME"
BN_mod_mul_montgomery, BN_MONT_CTX_new, BN_MONT_CTX_free, BN_MONT_CTX_set, BN_MONT_CTX_copy, BN_from_montgomery, BN_to_montgomery - Montgomery multiplication
"SYNOPSIS"
Header "SYNOPSIS" .Vb 1 #include <openssl/bn.h> \& BN_MONT_CTX *BN_MONT_CTX_new(void); void BN_MONT_CTX_free(BN_MONT_CTX *mont); \& int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *m, BN_CTX *ctx); BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from); \& int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_MONT_CTX *mont, BN_CTX *ctx); \& int BN_from_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont, BN_CTX *ctx); \& int BN_to_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont, BN_CTX *ctx); .Ve
"DESCRIPTION"
Header "DESCRIPTION" These functions implement Montgomery multiplication. They are used automatically when BN_mod_exp\|(3) is called with suitable input, but they may be useful when several operations are to be performed using the same modulus.

\fBBN_MONT_CTX_new() allocates and initializes a \s-1BN_MONT_CTX\s0 structure.

\fBBN_MONT_CTX_set() sets up the mont structure from the modulus m by precomputing its inverse and a value R.

\fBBN_MONT_CTX_copy() copies the \s-1BN_MONT_CTX\s0 from to to.

\fBBN_MONT_CTX_free() frees the components of the \s-1BN_MONT_CTX\s0, and, if it was created by BN_MONT_CTX_new(), also the structure itself. If mont is \s-1NULL,\s0 nothing is done.

\fBBN_mod_mul_montgomery() computes Mont(a,b):=a*b*R^-1 and places the result in r.

\fBBN_from_montgomery() performs the Montgomery reduction r = a*R^-1.

\fBBN_to_montgomery() computes Mont(a,R^2), i.e. a*R. Note that a must be nonnegative and smaller than the modulus.

For all functions, ctx is a previously allocated \s-1BN_CTX\s0 used for temporary variables.

"RETURN VALUES"
Header "RETURN VALUES" \fBBN_MONT_CTX_new() returns the newly allocated \s-1BN_MONT_CTX\s0, and \s-1NULL\s0 on error.

\fBBN_MONT_CTX_free() has no return value.

For the other functions, 1 is returned for success, 0 on error. The error codes can be obtained by ERR_get_error\|(3).

"WARNINGS"
Header "WARNINGS" The inputs must be reduced modulo m, otherwise the result will be outside the expected range.
"SEE ALSO"
Header "SEE ALSO" \fBERR_get_error\|(3), BN_add\|(3), \fBBN_CTX_new\|(3)
"HISTORY"
Header "HISTORY" \fBBN_MONT_CTX_init() was removed in OpenSSL 1.1.0
"COPYRIGHT"
Header "COPYRIGHT" Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.