Read an encrypted private key with bouncycastle/spongycastle

Question

I have a password protected, encrypted RSA private key, which was created with PyCrypto (2.6.1) and has according to their docs the following format: PrivateKeyInfo, PKCS#8 (DER SEQUENCE), PEM (RFC1423), see [https://www.dlitz.net/software/pycrypto/api/current/Crypto.PublicKey.RSA._RSAobj-class.html#exportKey].

How can I decrypt this RSA key with Bouncycastle/Spongycastle?

I've searched Google for quite a long time and only came up with results, that either won't work with version 1.50 (because PEMReader was deprecated and got removed) or with examples of PEMParser who seems to could not read this format. BTW: Is there any documentation on Bouncycastle I missed?

This is the header of my encrypted private key:

-----BEGIN PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,68949227DD8A502D
xyz...

I would really be thankful, if anyone could help me out!

Answer 1

To sum up what I found on this topic here and there :

Here is the final code if you want to get the modulus for example :

import java.io.FileReader;
import java.security.Security;
import java.security.KeyFactory
import org.bouncycastle.jce.provider.BouncyCastleProvider;
// Note that you need to add 'pkix' package. e.g. 'org.bouncycastle:bcpkix-jdk15on'
import org.bouncycastle.openssl.PEMEncryptedKeyPair;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.PEMDecryptorProvider;
import org.bouncycastle.openssl.PEMKeyPair;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
import org.bouncycastle.openssl.jcajce.JcePEMDecryptorProviderBuilder;

// For JcaPEMKeyConverter().setProvider("BC")
Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

// Using bcpkix-jdk14-1.48
PEMParser pemParser = new PEMParser(new FileReader(file));
Object object = pemParser.readObject();
JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC");
KeyPair kp;
if (object instanceof PEMEncryptedKeyPair)
{
    // Encrypted key - we will use provided password
    PEMEncryptedKeyPair ckp = (PEMEncryptedKeyPair) object;
    PEMDecryptorProvider decProv = new JcePEMDecryptorProviderBuilder().build(password.toCharArray());
    kp = converter.getKeyPair(ckp.decryptKeyPair(decProv));
}
else
{
    // Unencrypted key - no password needed
    PEMKeyPair ukp = (PEMKeyPair) object;
    kp = converter.getKeyPair(ukp);
}

// RSA
KeyFactory keyFac = KeyFactory.getInstance("RSA");
RSAPrivateCrtKeySpec privateKey = keyFac.getKeySpec(kp.getPrivate(), RSAPrivateCrtKeySpec.class);

return privateKey;

And then you can call for example :

privateKey.getModulus();

Answer 2

The following static method will handle all the following PEM encoding styles for encrypted private keys:

-----BEGIN ENCRYPTED PRIVATE KEY-----
-----BEGIN PRIVATE KEY-----
-----BEGIN EC PRIVATE KEY-----

First ensure that you've registered BC as a security provider then you can use this method:

  static public PrivateKey stringToPrivateKey(String s, String password)
      throws IOException, PKCSException {

    PrivateKeyInfo pki;

    try (PEMParser pemParser = new PEMParser(new StringReader(s))) {

      Object o = pemParser.readObject();

      if (o instanceof PKCS8EncryptedPrivateKeyInfo) {

        PKCS8EncryptedPrivateKeyInfo epki = (PKCS8EncryptedPrivateKeyInfo) o;

        JcePKCSPBEInputDecryptorProviderBuilder builder =
            new JcePKCSPBEInputDecryptorProviderBuilder().setProvider(bc);

        InputDecryptorProvider idp = builder.build(password.toCharArray());

        pki = epki.decryptPrivateKeyInfo(idp);
      } else if (o instanceof PEMEncryptedKeyPair) {

        PEMEncryptedKeyPair epki = (PEMEncryptedKeyPair) o;
        PEMKeyPair pkp = epki.decryptKeyPair(new BcPEMDecryptorProvider(password.toCharArray()));

        pki = pkp.getPrivateKeyInfo();
      } else {
        throw new PKCSException("Invalid encrypted private key class: " + o.getClass().getName());
      }

      JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider(bc);
      return converter.getPrivateKey(pki);
    }
  }