Convert OpenSwan key to RSA key

openswan-to-rsa.c

#include <stdio.h>
#include <openssl/rsa.h>
#include <openssl/bn.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

int main(void) {
        BIGNUM *bn;
        RSA *rsa = RSA_new();
        bn = BN_new();
        BN_set_word(bn, <exponent, such as 0x010001 or 0x3>);
        rsa->e = bn;
        bn = NULL;
        BN_hex2bn(&bn,"<modulus in hex without 0x>");
        rsa->n = bn;

        EVP_PKEY *pkey = EVP_PKEY_new();
        EVP_PKEY_set1_RSA(pkey, rsa);

        PEM_write_PUBKEY(stdout, pkey);
}