-extern size_t rsa_size(rsa_t *rsa);
-extern bool rsa_public_encrypt(rsa_t *rsa, void *in, size_t len, void *out) __attribute__((__warn_unused_result__));
-extern bool rsa_private_decrypt(rsa_t *rsa, void *in, size_t len, void *out) __attribute__((__warn_unused_result__));
+extern size_t rsa_size(const rsa_t *rsa);
+extern bool rsa_public_encrypt(rsa_t *rsa, const void *in, size_t len, void *out) __attribute__((__warn_unused_result__));
+extern bool rsa_private_decrypt(rsa_t *rsa, const void *in, size_t len, void *out) __attribute__((__warn_unused_result__));