Question

I have generated a private key and encrypted it with a password. Now I want to load it to EncryptedPrivateKeyInfo, so that I can construct and export it into a PEM format file. Below is the code I use,

final CertAndKeyGen keypair = new CertAndKeyGen("RSA", "SHA1WithRSA", null);
final X500Name x500Name =
    new X500Name("IN", "AP", "HYD", "TEST", "TEST_ORG", "[e-mail]");
keypair.generate(1024);
final PrivateKey privKey = keypair.getPrivateKey();
final X509Certificate[] chain = new X509Certificate[1];
long validity = 123;
chain[0] = keypair.getSelfCertificate(x500Name, new Date(), 
    validity * 24 * 60 * 60);
Key key =  new SecretKeySpec(password.getBytes(), ALGO);
Cipher c = Cipher.getInstance(ALGO);
c.init(Cipher.ENCRYPT_MODE, key);
byte[] encVal = c.doFinal(privKey.getEncoded());
AlgorithmParameters params = AlgorithmParameters.getInstance("DES");
params.init(encVal); // <--- exception thrown here
EncryptedPrivateKeyInfo encinfo = new EncryptedPrivateKeyInfo(params, encVal);

// displaying encrypting value
String encryptedValue = Base64.encodeBase64String(encinfo.getEncoded());
System.out.println(encryptedValue);

But while executing the above code, I get the below exception

java.io.IOException: DER input not an octet string
  at sun.security.util.DerInputStream.getOctetString(DerInputStream.java:233)
  at com.sun.crypto.provider.SunJCE_t.a(DashoA13*..)
  at com.sun.crypto.provider.DESParameters.engineInit(DashoA13*..)
  at java.security.AlgorithmParameters.init(AlgorithmParameters.java:260)

in the line params.init(encVal);. I don’t get what’s going wrong from the exception. Any help or suggestion will be really appreciated. Thanks in advance.

Answer 1

A PKCS #8 file containing an encrypted private key has the following ASN.1 structure:

EncryptedPrivateKeyInfo ::= SEQUENCE {
  encryptionAlgorithm EncryptionAlgorithmIdentifier,
  encryptedData EncryptedData }

Notice how the encrypted data is only part of the total data package. You need to include this data in a sequence along with the encryption algorithm identifier. Your code above produces only the encryptedData part.

---

I would suggest you consider using BouncyCastle. It looks like they may have improved support for PKCS#8 recently. Here’s some sample code:

KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
KeyPair keyPair = generator.generateKeyPair();

final PrivateKey privKey = keyPair.getPrivate();

JceOpenSSLPKCS8EncryptorBuilder builder =
    new JceOpenSSLPKCS8EncryptorBuilder(PKCS8Generator.PBE_SHA1_3DES);

builder.setIterationCount(10000);
builder.setPasssword("Hello, World!".toCharArray());

OutputEncryptor outputEncryptor = builder.build();    
PKCS8Generator pkcs8Generator =
    new JcaPKCS8Generator(privKey, outputEncryptor);

try (PemWriter writer = new PemWriter(new PrintWriter(System.out))) {
  writer.writeObject(pkcs8Generator);
}

This will output an encrypted private key:

-----BEGIN ENCRYPTED PRIVATE KEY-----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-----END ENCRYPTED PRIVATE KEY-----