NAME
BN_MONT_CTX_new,
BN_MONT_CTX_free,
BN_MONT_CTX_set,
BN_MONT_CTX_set_locked,
BN_MONT_CTX_copy,
BN_mod_mul_montgomery,
BN_from_montgomery,
BN_to_montgomery —
Montgomery multiplication
SYNOPSIS
#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_set_locked(BN_MONT_CTX
**pmont, int lock, 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,
const BIGNUM *a, const BIGNUM
*b, BN_MONT_CTX *mont, BN_CTX
*ctx);
int
BN_from_montgomery(BIGNUM *r,
const BIGNUM *a, BN_MONT_CTX
*mont, BN_CTX *ctx);
int
BN_to_montgomery(BIGNUM *r,
const BIGNUM *a, BN_MONT_CTX
*mont, BN_CTX *ctx);
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.
BN_MONT_CTX_new()
allocates and initializes a BN_MONT_CTX structure.
BN_MONT_CTX_set()
sets up the mont structure from the modulus
m by precomputing its inverse and a value R.
BN_MONT_CTX_set_locked()
is a wrapper around BN_MONT_CTX_new() and
BN_MONT_CTX_set() that is useful if more than one
thread intends to use the same BN_MONT_CTX and none of
these threads is exclusively responsible for creating and initializing the
context. BN_MONT_CTX_set_locked() first acquires the
specified lock using
CRYPTO_lock(3). If *pmont already
differs from NULL, no action occurs. Otherwise, a
new BN_MONT_CTX is allocated with
BN_MONT_CTX_new(), set up with
BN_MONT_CTX_set(), and a pointer to it is stored in
*pmont. Finally, the lock is
released.
BN_MONT_CTX_copy()
copies the BN_MONT_CTX from to
to.
BN_MONT_CTX_free()
frees the components of the BN_MONT_CTX, and, if it
was created by BN_MONT_CTX_new(), also the structure
itself. If mont is a NULL
pointer, no action occurs.
BN_mod_mul_montgomery()
computes
and places the result in r.
BN_from_montgomery()
performs the Montgomery reduction
BN_to_montgomery()
computes
Note that a must be non-negative and smaller than the modulus.
For all functions, ctx is a previously allocated BN_CTX used for temporary variables.
Warning: The inputs must be reduced modulo m, otherwise the result will be outside the expected range.
RETURN VALUES
BN_MONT_CTX_new() returns the newly
allocated BN_MONT_CTX or NULL
on error.
BN_MONT_CTX_set_locked() returns a pointer
to the existing or newly created context or NULL on
error.
For the other functions, 1 is returned for success or 0 on error. The error codes can be obtained by ERR_get_error(3).
SEE ALSO
HISTORY
BN_MONT_CTX_new(),
BN_MONT_CTX_free(),
BN_MONT_CTX_set(),
BN_mod_mul_montgomery(),
BN_from_montgomery(), and
BN_to_montgomery() first appeared in SSLeay 0.6.1
and have been available since OpenBSD 2.4.
BN_MONT_CTX_copy() first appeared in
SSLeay 0.9.1 and has been available since OpenBSD
2.6.
BN_MONT_CTX_set_locked() first appeared in
OpenSSL 0.9.8 and has been available since OpenBSD
4.0.