int BN_mod_exp2_mont(BIGNUM *r, BIGNUM *a1, BIGNUM *p1,BIGNUM *a2,
BIGNUM *p2,BIGNUM *m,BN_CTX *ctx,BN_MONT_CTX *m_ctx);
int BN_mod_exp_simple(BIGNUM *r, BIGNUM *a, BIGNUM *p,
BIGNUM *m,BN_CTX *ctx);
int BN_mask_bits(BIGNUM *a,int n);
int BN_mod_exp2_mont(BIGNUM *r, BIGNUM *a1, BIGNUM *p1,BIGNUM *a2,
BIGNUM *p2,BIGNUM *m,BN_CTX *ctx,BN_MONT_CTX *m_ctx);
int BN_mod_exp_simple(BIGNUM *r, BIGNUM *a, BIGNUM *p,
BIGNUM *m,BN_CTX *ctx);
int BN_mask_bits(BIGNUM *a,int n);