Decode/Read a CSR (Certificate Signing Request) Us

Question

I am generating a CSR (certificate signing request) using code without an issue with the appropriate information. I need pointers to figure out how to read the CSR content using Java and/or BouncyCastle.

Any pointers or ideas are appreciated.

Answer 1

Figured it out:

1. Convert the CSR PEM to a PKCS10CertificationRequest
2. Get the X500Name instance by accessing the getSubject() method from PKCS10CertificationRequest instance
3. Iterate over the RDN[] array and get the specific field you want using one of the ASN1ObjectIdentifier's (for example COUNTRY is 2.5.4.6)

Here is the code:

public class EncryptDecrypt {
    private Logger LOG = LoggerFactory.getLogger(EncryptDecrypt.class);
    private final String COUNTRY = "2.5.4.6";
    private final String STATE = "2.5.4.8";
    private final String LOCALE = "2.5.4.7";
    private final String ORGANIZATION = "2.5.4.10";
    private final String ORGANIZATION_UNIT = "2.5.4.11";
    private final String COMMON_NAME = "2.5.4.3";


    @Test
    public void testReadCertificateSigningRequest() {
        String csrPEM = "-----BEGIN CERTIFICATE REQUEST-----\n" +
                "MIICwjCCAaoCAQAwfTELMAkGA1UEBhMCVVMxEDAOBgNVBAgTB0Zsb3JpZGExEzAR\n" +
                "BgNVBAcTCkJvY2EgUmF0b24xGzAZBgNVBAoTEkxvb25leSBUb29ucywgSW5jLjEU\n" +
                "MBIGA1UECxMLRGV2ZWxvcG1lbnQxFDASBgNVBAMTC2V4YW1wbGUuY29tMIIBIjAN\n" +
                "BgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAiJCj31d1Rp+aKz/GTkedaiS/VSCc\n" +
                "PRARYgXukobjgBHx46HjldAcfg/DoANn5lEQaFxaIZJLbZ/AdLUyw/hUbU0CjWXv\n" +
                "pN3Ep3o9XgRTPkIFoI22VOI/O2ZLjBq/E4DWyVmv+vG6BK0LRh7hykzPCw6KIRR9\n" +
                "NCmUMJMQX5d5P/r1lR5H399pnLcLsrHoWDwBSEDgkGWyxnvEB0+/bIz42T3qnlFt\n" +
                "7avarxlHG2p5DoRTf8GJ+6imY88ZeBW/Nk18aDINsAHWLv383JICIAsZ3VuMk8m/\n" +
                "Z/Z5b21zIuZECDJjZjvAAjr/shVLB+Pck5+HJy6tqj79MJOQu+jKIrK8VwIDAQAB\n" +
                "oAAwDQYJKoZIhvcNAQEFBQADggEBAGtuAAHG4OC9jSRjGWSqfMXTDMz9tgekDREA\n" +
                "SYv5QIrOXsMzwbgDw8LxRJZEskl4JJOnjwEvUXWUF1M6XmG2h358nOnrkOlsumHw\n" +
                "Tx5gGSr6S6aJO/HG46erctE8aWpnFZYMfuEkul4ApsIufL7Bxqs3NHZWcrWBlLIP\n" +
                "aVCKx1FPRMC36Tj3EslbuUB/iTRt90Nfq1IxHMIKiwCiSNJSqfRVLANhI8MUbOjB\n" +
                "CBly1wcH68WWNkyvHVvbcF/B9AfYG9AqWjZjygKpyf81VZWctXhDc8UtomqrblXN\n" +
                "mvz4RKpIhZQLuuxlBrdzJkPm2sOdtdZghebCRRVWdjsig4sylgQ=\n" +
                "-----END CERTIFICATE REQUEST-----";

        PKCS10CertificationRequest csr = convertPemToPKCS10CertificationRequest(csrPEM);

        X500Name x500Name = csr.getSubject();
        System.out.println("x500Name is: " + x500Name + "\n");

        // country is 2.5.4.6
        System.out.println("COUNTRY: " + getX500Field(COUNTRY, x500Name));
        // state is 2.5.4.8
        System.out.println("STATE: " + getX500Field(STATE, x500Name));
        // locale is 2.5.4.7
        System.out.println("LOCALE: " + getX500Field(LOCALE, x500Name));


    }

    private String getX500Field(String asn1ObjectIdentifier, X500Name x500Name) {
        RDN[] rdnArray = x500Name.getRDNs(new ASN1ObjectIdentifier(asn1ObjectIdentifier));
        String retVal = null;
        for (RDN item : rdnArray) {
            retVal = item.getFirst().getValue().toString();
        }

        return retVal;
    }

    private PKCS10CertificationRequest convertPemToPKCS10CertificationRequest(String pem) {
        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
        PKCS10CertificationRequest csr = null;
        ByteArrayInputStream pemStream = null;
        try {
            pemStream = new ByteArrayInputStream(pem.getBytes("UTF-8"));
        } catch (UnsupportedEncodingException ex) {
            LOG.error("UnsupportedEncodingException, convertPemToPublicKey", ex);
        }

        Reader pemReader = new BufferedReader(new InputStreamReader(pemStream));
        PEMParser pemParser = new PEMParser(pemReader);

        try {
            Object parsedObj = pemParser.readObject();

            System.out.println("PemParser returned: " + parsedObj);

            if (parsedObj instanceof PKCS10CertificationRequest) {
                csr = (PKCS10CertificationRequest) parsedObj;

            }
        } catch (IOException ex) {
            LOG.error("IOException, convertPemToPublicKey", ex);
        }

        return csr;
    }

    private String toPEM(Object key) {
        StringWriter sw = new StringWriter();
        PEMWriter pem = new PEMWriter(sw);
        try {
            pem.writeObject(key);
            pem.close();
        } catch (IOException e) {
            System.out.printf("IOException: %s%n", e);
        }
        return sw.toString();
    }
}