JNIEXPORT jbyteArray function(JNIEnv* env, jbyteArray array) {
    int length = (*env)->GetArrayLength(env, array);

    jbyte data[256];

    (*env)->GetByteArrayRegion(env, array, 0, 256, data);
    //also tried
    //jbyte *data = (jbyte*) (*env)->GetByteArrayElements(env, array, NULL);
}

//there is some openSSL stuff here that sets up a pointer to an RSA struct called keys that is size bytes large

jbyteArray result = (*env)->NewByteArray(env, size);

(*env)->SetByteArrayRegion(env, result, 0, size, (jbyte*)keys;

JNIEXPORT jbyteArray function(JNIEnv* env, jbyteArray array)

JNIEXPORT jbyteArray function(JNIEnv* env, jclass cls, jbyteArray array)

JNIEXPORT jbyteArray function(JNIEnv* env, jobject obj, jbyteArray array)

EVP_pkey *pkey = EVP_PKEY_new();
EVP_PKEY_assign_RSA(pkey, rsa);