RSA_size - get RSA modulus size
#include <openssl/rsa.h>
int RSA_size(const RSA *rsa);
This function returns the RSA modulus size in bytes. It can be used to determine how much memory must be allocated for an RSA encrypted value.
rsa->n must not be NULL.
The size in bytes.
RSA_size() is available in all versions of SSLeay and OpenSSL.