#include <openssl/bn.h>

BIGNUM *BN_new(void);

int BN_hex2bn(BIGNUM **a, const char *str);

int BN_print_fp(FILE *fp, const BIGNUM *a);

       BN_new() allocates and initializes a BIGNUM structure.

       BN_hex2bn() takes as many characters as possible from the string str, including the
       leading character '-' which means negative, to form a valid hexadecimal number
       representation and converts them to a BIGNUM and stores it in **a. If *a is NULL, a
       new BIGNUM is created. If a is NULL, it only computes the length of valid
       representation.  A "negative zero" is converted to zero.  BN_dec2bn() is the same
       using the decimal system.

       BN_hex2bn() and BN_dec2bn() return the number of characters used in parsing, or 0 on
       error, in which case no new BIGNUM will be created.

       BN_print() and BN_print_fp() write the hexadecimal encoding of a, with a leading '-'
       for negative numbers, to the BIO or FILE fp.

       BN_print_fp() and BN_print() return 1 on success, 0 on write errors.

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BN_CTX *BN_CTX_new(void);

int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);

int BN_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx);

int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx);

       BN_CTX_new() allocates and initializes a BN_CTX structure.

       BN_add() adds a and b and places the result in r ("r=a+b").  r may be the same BIGNUM
       as a or b.

       BN_mul() multiplies a and b and places the result in r ("r=a*b").  r may be the same
       BIGNUM as a or b.  For multiplication by powers of 2, use BN_lshift(3).

       BN_mod_exp() computes a to the p-th power modulo m ("r=a^p % m"). This function uses
       less time and space than BN_exp().

       For all functions, ctx is a previously allocated BN_CTX used for temporary variables;
       see BN_CTX_new(3).

       Unless noted otherwise, the result BIGNUM must be different from the arguments.

       For all functions, 1 is returned for success, 0 on error.

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int BN_cmp(BIGNUM *a, BIGNUM *b);

       BN_cmp() compares the numbers a and b.

       BN_cmp() returns -1 if a < b, 0 if a == b and 1 if a > b.