where is the struct RSA defined??

[霏霏]

In the source code of openssh(my source code is 6.0 for Openbsd）：
The content below is Rsa.h

#ifndef RSA_H
#define RSA_H

#include <openssl/bn.h>
#include <openssl/rsa.h>

void     rsa_public_encrypt(BIGNUM *, BIGNUM *, RSA *);
int     rsa_private_decrypt(BIGNUM *, BIGNUM *, RSA *);
void     rsa_generate_additional_parameters(RSA *);

#endif                /* RSA_H */

Question:
    Where is the file openssl/rsa.h? So where is the struct RSA defined??