Generate CSR from private key or Key Store

Question

How can i generate CSR from the Key Store.

I have generated CSR from key pair. Below is my code.

public static PKCS10CertificationRequest generateCSR(KeyPair keyPair, String cn) throws IOException,
        OperatorCreationException {
    String principal = String.format(CN_PATTERN, cn);

    ContentSigner signer = new JCESigner (keyPair.getPrivate(),DEFAULT_SIGNATURE_ALGORITHM);

    PKCS10CertificationRequestBuilder csrBuilder = new JcaPKCS10CertificationRequestBuilder(
            new X500Name(principal), keyPair.getPublic());
    ExtensionsGenerator extensionsGenerator = new ExtensionsGenerator();
    extensionsGenerator.addExtension(Extension.basicConstraints, true, new BasicConstraints(
            true));
    csrBuilder.addAttribute(PKCSObjectIdentifiers.pkcs_9_at_extensionRequest,
            extensionsGenerator.generate());
    Log.e("csr builder ","csr "+csrBuilder.toString());
    PKCS10CertificationRequest csr = csrBuilder.build(signer);

    return csr;
}

But i cannot generate CSR from Keystore(Private Key). Is there any way i can generate key pair from Keystore?

Please help me.Thanks in Advance.

Answer 1

Your code is compatible with Android KeyStore. You just need to generate the KeyPair into the Keystore

The KeyStore is available from Android 4.3 (API level 18). There are slight differences between versions

Android >=18 < 23

KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(context)
                .setAlias(alias)
                .setSubject(new X500Principal("CN=" + alias + ", O=Android Authority"))
                .setSerialNumber(BigInteger.ONE)
                .setStartDate(start.getTime())
                .setEndDate(end.getTime())
                .build();

KeyPairGenerator kpg = KeyPairGenerator.getInstance(
                KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore");

kpg.initialize(spec);
KeyPair keyPair = kpg.generateKeyPair();

Android >=23

KeyPairGenerator kpg = KeyPairGenerator.getInstance(
                KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore");


kpg.initialize(new KeyGenParameterSpec.Builder(
                alias,
                KeyProperties.PURPOSE_SIGN | KeyProperties.PURPOSE_VERIFY)
                .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA512)
                .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PKCS1)
                .build());

KeyPair keyPair = kpg.generateKeyPair();