How to decrypt a private key in Java (without BC o

Question

Is it possible decrypt an encrypted RSA (or others, shouldn't matter) private keys using JCE and/or BouncyCastle provider (not using openssl bundle)?

I can read unencrypted keys just fine using PrivateKeyFactory.

Googling this gets me through examples of using PEMReader (from BC openssl bundle) that has a password applied to it, but - don't want to use openssl bundle, don't necessarily want to use PEM format, and I can decode PEM using PemReader (from provider bundle). It's what can I do with it afterwards is the question.

I'm looking for some mega-function, or a series thereof that can do it, i.e. I am not looking into parsing the ASN1 of the encrypted key, figuring out the encryption method, passing the input through the cipher, etc.

Answer 1

If you have an encrypted PKCS#8 key in binary format (i.e. not in PEM format) the following code shows how to retrieve the private key:

public PrivateKey decryptKey(byte[] pkcs8Data, char[] password) throws Exception {
    PBEKeySpec pbeSpec = new PBEKeySpec(password);
    EncryptedPrivateKeyInfo pkinfo = new EncryptedPrivateKeyInfo(pkcs8Data);
    SecretKeyFactory skf = SecretKeyFactory.getInstance(pkinfo.getAlgName());
    Key secret = skf.generateSecret(pbeSpec);
    PKCS8EncodedKeySpec keySpec = pkinfo.getKeySpec(secret);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    return kf.generatePrivate(keySpec);
}

If you have a PEM format, remove the header (first line), the footer(last line) et convert the remaining content from base64 to regular byte array.