How to read DER DSA private key to AsymmetricKeyParameter in bouncy castle (Java)

Question

How to read DER file with private DSA key (4096 bit) into AsymmetricKeyParameter for usage in DSASigner ?

The following code I tried:

 byte[] privateKeyBytes = FileUtils.readFileToByteArray(new File(
                    "sign-key-private.der"));
 AsymmetricKeyParameter privateKey = PrivateKeyFactory
                    .createKey(privateKeyBytes);

Result is an exception:

java.lang.IllegalArgumentException: unknown object in getInstance: org.bouncycastle.asn1.ASN1Integer
    at org.bouncycastle.asn1.ASN1Sequence.getInstance(Unknown Source)
    at org.bouncycastle.asn1.x509.AlgorithmIdentifier.getInstance(Unknown Source)
    at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.<init>(Unknown Source)
    at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.getInstance(Unknown Source)
    at org.bouncycastle.crypto.util.PrivateKeyFactory.createKey(Unknown Source)
    at test.security.core.Program.main(Program.java:41)

Answer 1

The workaround solution I have finally used was to convert key to PEM format and use the following:

 @Cleanup
 FileReader privateKeyReader = new FileReader(new File("key.pem"));
 @Cleanup
 PEMParser parser = new PEMParser(privateKeyReader);

 PEMKeyPair keyPair = (PEMKeyPair) parser.readObject();
 AsymmetricKeyParameter privateKey = PrivateKeyFactory
     .createKey(keyPair.getPrivateKeyInfo());
 AsymmetricKeyParameter publicKey = PublicKeyFactory
     .createKey(keyPair.getPublicKeyInfo());

Answer 2

byte[] privateKeyBytes = FileUtils.readFileToByteArray(new File("sign-key-private.der"));
KeyFactory kf = KeyFactory.getInstance("RSA", "BC");
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(privateKeyBytes);
RSAPrivateKey rsaKey = (RSAPrivateKey) kf.generatePrivate(keySpec);
AsymmetricKeyParameter privateKeyParameter = new RSAKeyParameters(true, rsaKey.getModulus(), rsaKey.getPrivateExponent());