HP Open Source Security for OpenVMS Volume 2: HP SSL for OpenVMS > CRYPTO Application Programming Interface (API) Reference

BN_mod_mul_reciprocal

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NAME

BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init, BN_RECP_CTX_free, BN_RECP_CTX_set — modular multiplication using reciprocal

Synopsis

#include <openssl/bn.h> 
BN_RECP_CTX
*BN_RECP_CTX_new(void); 
void BN_RECP_CTX_init(BN_RECP_CTX
*recp); 
void BN_RECP_CTX_free(BN_RECP_CTX *recp); 
int
BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx); 
int
BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
BN_CTX *ctx); 
int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM
*a, BIGNUM *b, BN_RECP_CTX *recp, BN_CTX *ctx);

DESCRIPTION

BN_mod_mul_reciprocal() can be used to perform an efficient BN_mod_mul(3) operation when the operation will be performed repeatedly with the same modulus. It computes r=(a*b)%m using recp=1/m, which is set as described below. ctx is a previously allocated BN_CTX used for temporary variables.

BN_RECP_CTX_new() allocates and initializes a BN_RECP structure. BN_RECP_CTX_init() initializes an existing uninitialized BN_RECP.

BN_RECP_CTX_free() frees the components of the BN_RECP, and, if it was created by BN_RECP_CTX_new(), also the structure itself.

BN_RECP_CTX_set() stores m in recp and sets it up for computing 1/m and shifting it left by BN_num_bits(m)+1 to make it an integer. The result and the number of bits it was shifted left will later be stored in recp.

BN_div_recp() divides a by m using recp. It places the quotient in dv and the remainder in rem.

The BN_RECP_CTX structure is defined as follows: 

 typedef struct bn_recp_ctx_st
	{
	BIGNUM N;	/* the divisor */
	BIGNUM Nr;	/* the reciprocal */
	int num_bits;
	int shift;
	int flags;
	} BN_RECP_CTX;

It cannot be shared between threads.

RETURN VALUES

BN_RECP_CTX_new() returns the newly allocated BN_RECP_CTX, and NULL on error.

BN_RECP_CTX_init() and BN_RECP_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).

SEE ALSO

bn(3), ERR_get_error(3), BN_add(3), BN_CTX_new(3)

HISTORY

BN_RECP_CTX was added in SSLeay 0.9.0. Before that, the function BN_reciprocal() was used instead, and the BN_mod_mul_reciprocal() arguments were different.



BN_mod_mul_montgomery
  		 


BN_new