BN_mod_mul_reciprocal 3 2003-07-24 0.9.9-dev OpenSSL

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

LIBRARY

libcrypto, -lcrypto

SYNOPSIS


 #include 


 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

_B_N___m_o_d___m_u_l___r_e_c_i_p_r_o_c_a_l_(_) can be used to perform an efficient _B_N___m_o_d___m_u_l(3) operation when the operation will be performed repeatedly with the same modulus. It computes rr=(aa*bb)%mm using rreeccpp=1/mm, which is set as described below. ccttxx is a previously allocated BBNN__CCTTXX used for temporary variables.

_B_N___R_E_C_P___C_T_X___n_e_w_(_) allocates and initializes a BBNN__RREECCPP structure. _B_N___R_E_C_P___C_T_X___i_n_i_t_(_) initializes an existing uninitialized BBNN__RREECCPP.

_B_N___R_E_C_P___C_T_X___f_r_e_e_(_) frees the components of the BBNN__RREECCPP, and, if it was created by _B_N___R_E_C_P___C_T_X___n_e_w_(_), also the structure itself.

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

_B_N___d_i_v___r_e_c_p_(_) divides aa by mm using rreeccpp. It places the quotient in ddvv and the remainder in rreemm.

The BBNN__RREECCPP__CCTTXX 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

_B_N___R_E_C_P___C_T_X___n_e_w_(_) returns the newly allocated BBNN__RREECCPP__CCTTXX, and NULL on error.

_B_N___R_E_C_P___C_T_X___i_n_i_t_(_) and _B_N___R_E_C_P___C_T_X___f_r_e_e_(_) have no return values.

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

SEE ALSO

_o_p_e_n_s_s_l___b_n(3), _E_R_R___g_e_t___e_r_r_o_r(3), _B_N___a_d_d(3), _B_N___C_T_X___n_e_w(3)

HISTORY

BBNN__RREECCPP__CCTTXX was added in SSLeay 0.9.0. Before that, the function _B_N___r_e_c_i_p_r_o_c_a_l_(_) was used instead, and the _B_N___m_o_d___m_u_l___r_e_c_i_p_r_o_c_a_l_(_) arguments were different.