-int BN_bn2mpi(BIGNUM *a, unsigned char *to);
-int BN_sub(BIGNUM *r, BIGNUM *a, BIGNUM *b);
-int BN_usub(BIGNUM *r, BIGNUM *a, BIGNUM *b);
-int BN_uadd(BIGNUM *r, BIGNUM *a, BIGNUM *b);
-int BN_add(BIGNUM *r, BIGNUM *a, BIGNUM *b);
-int BN_mod(BIGNUM *rem, BIGNUM *m, BIGNUM *d, BN_CTX *ctx);
-int BN_div(BIGNUM *dv, BIGNUM *rem, BIGNUM *m, BIGNUM *d, BN_CTX *ctx);
-int BN_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b,BN_CTX *ctx);
+int BN_bn2mpi(const BIGNUM *a, unsigned char *to);
+int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
+int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
+int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
+int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
+int BN_mod(BIGNUM *rem, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx);
+int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
+ BN_CTX *ctx);
+int BN_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx);