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BN_mod_mul_montgomery(3) OpenSSL BN_mod_mul_montgomery(3) NAME
BN_mod_mul_montgomery, BN_MONT_CTX_new, BN_MONT_CTX_init, BN_MONT_CTX_free, BN_MONT_CTX_set, BN_MONT_CTX_copy, 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_init(BN_MONT_CTX *ctx); 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); 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_init() initializes an existing uninitialized BN_MONT_CTX. BN_MONT_CTX_set() sets up the mont structure from the modulus m by precomputing its inverse and a value R. 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. BN_mod_mul_montgomery() computes Mont(a,b):=a*b*R^-1 and places the result in r. BN_from_montgomery() performs the Montgomery reduction r = a*R^-1. BN_to_montgomery() computes Mont(a,R^2), i.e. a*R. 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. The BN_MONT_CTX structure is defined as follows: typedef struct bn_mont_ctx_st { int ri; /* number of bits in R */ BIGNUM RR; /* R^2 (used to convert to Montgomery form) */ BIGNUM N; /* The modulus */ BIGNUM Ni; /* R*(1/R mod N) - N*Ni = 1 * (Ni is only stored for bignum algorithm) */ BN_ULONG n0; /* least significant word of Ni */ int flags; } BN_MONT_CTX; BN_to_montgomery() is a macro. RETURN VALUES
BN_MONT_CTX_new() returns the newly allocated BN_MONT_CTX, and NULL on error. BN_MONT_CTX_init() and BN_MONT_CTX_free() have no return values. For the other functions, 1 is returned for success, 0 on error. The error codes can be obtained by ERR_get_error(3). WARNING
The inputs must be reduced modulo m, otherwise the result will be outside the expected range. SEE ALSO
bn(3), ERR_get_error(3), BN_add(3), BN_CTX_new(3) HISTORY
BN_MONT_CTX_new(), BN_MONT_CTX_free(), BN_MONT_CTX_set(), BN_mod_mul_montgomery(), BN_from_montgomery() and BN_to_montgomery() are available in all versions of SSLeay and OpenSSL. BN_MONT_CTX_init() and BN_MONT_CTX_copy() were added in SSLeay 0.9.1b. 1.0.1e 2013-02-11 BN_mod_mul_montgomery(3)
