public Boolean decryptSessionKey() {

    // first, base64 decode the session key
    String sslString = "openssl base64 -d -in enc_sesskey -out temp";

    try {
        Process p = Runtime.getRuntime().exec(sslString);
    } catch (IOException e2) {
        e2.printStackTrace();
    }

    // now we can decrypt it
    try {
        sslString = "openssl rsautl -in temp -inkey privkey.pem -decrypt";
        Process p = Runtime.getRuntime().exec(sslString);
        BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));

        try {
            String s;
            while ((s = stdInput.readLine()) != null) {
                decrypted_session_password = s;
                writeToFile(decrypted_sesskey, s);
            }
            return true;

        } catch (Exception e) {
            return false;
        }
    } catch (IOException e1) {
        return false;
    } catch (Exception e) {
        return false;
    }
}

public Boolean encryptSessionKey(Cert receiver_cert) {

    String sslString =
        "openssl rsautl base64 -in sesskey -out temp -inkey cert.pem -encrypt -certin";

    // run this openssl encryption. Note that it will not yet be base64 encoded
    try {
        Process p = Runtime.getRuntime().exec(sslString);
    } catch (IOException e2) {
        e2.printStackTrace();
    }

    // now we base64-encode the encrypted file
    sslString = "openssl base64 -in temp -out enc_sesskey";

    try {
        Process p = Runtime.getRuntime().exec(sslString);
    } catch (IOException e1) {return false;
    } catch (Exception e) {return false;
    }

    return true;
}

openssl rsautl -encrypt -in sesskey -inkey cert.pem -certin -out temp
openssl base64 -e -in temp -out enc_sesskey

openssl base64 -d -in enc_sesskey -out temp
openssl rsautl -decrypt -in temp -inkey privkey.pem -out sesskey2