=pod =head1 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 =head1 SYNOPSIS #include BN_RECP_CTX *BN_RECP_CTX_new(void); 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); =head1 DESCRIPTION BN_mod_mul_reciprocal() can be used to perform an efficient L operation when the operation will be performed repeatedly with the same modulus. It computes B=(B*B)%B using B=1/B, which is set as described below. B is a previously allocated B used for temporary variables. BN_RECP_CTX_new() allocates and initializes a B structure. BN_RECP_CTX_init() initializes an existing uninitialized B. BN_RECP_CTX_free() frees the components of the B, and, if it was created by BN_RECP_CTX_new(), also the structure itself. BN_RECP_CTX_set() stores B in B and sets it up for computing 1/B and shifting it left by BN_num_bits(B)+1 to make it an integer. The result and the number of bits it was shifted left will later be stored in B. BN_div_recp() divides B by B using B. It places the quotient in B and the remainder in B. The B structure cannot be shared between threads. =head1 RETURN VALUES BN_RECP_CTX_new() returns the newly allocated B, 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 L. =head1 REMOVED FUNCTIONALITY void BN_RECP_CTX_init(BN_RECP_CTX *recp); BN_RECP_CTX_init() is no longer available as of OpenSSL 1.1.0. It was used to initialize an existing uninitialized B. Typically this would be done as follows: BN_RECP_CTX ctx; BN_RECP_CTX_init(&ctx); Applications should replace use of BN_RECP_CTX_init with BN_RECP_CTX_new instead: BN_RECP_CTX *ctx; ctx = BN_RECP_CTX_new(); if(!ctx) /* Handle error */ ... BN_RECP_CTX_free(ctx); =head1 SEE ALSO L, L, L, L =head1 HISTORY B 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_RECP_CTX_init was removed in OpenSSL 1.1.0 =cut