BouncyCastle Alternative to Decrypt a Encrypted p8 file

Question

I am generating RSA PrivateKey using openSSL in command prompt.

$ openssl genrsa 2048 | openssl pkcs8 -topk8 -inform PEM -out rsa_key.p8

Now this private key needs to decrypt using passphrase to get PrivateKey object which can be used for Authentication. Sample bouncycastle code which is working :

public static PrivateKey getKey()
            throws Exception {
         String filename = "C:\\Snowflake\\rsa_key.p8";
         Security.addProvider(new BouncyCastleProvider());
        PrivateKeyInfo privateKeyInfo = null;
        Security.addProvider(new BouncyCastleProvider());
        // Read an object from the private key file.
         PEMParser pemParser = new PEMParser(new FileReader(Paths.get(filename).toFile()));
            Object pemObject = pemParser.readObject();
        if (pemObject instanceof PKCS8EncryptedPrivateKeyInfo) {
            // Handle the case where the private key is encrypted.
            PKCS8EncryptedPrivateKeyInfo encryptedPrivateKeyInfo = (PKCS8EncryptedPrivateKeyInfo) pemObject;
            String passphrase = getPrivateKeyPassphrase();
            InputDecryptorProvider pkcs8Prov = new JceOpenSSLPKCS8DecryptorProviderBuilder().build(passphrase.toCharArray());
            privateKeyInfo = encryptedPrivateKeyInfo.decryptPrivateKeyInfo(pkcs8Prov);
        } else if (pemObject instanceof PrivateKeyInfo) {
            // Handle the case where the private key is unencrypted.
            privateKeyInfo = (PrivateKeyInfo) pemObject;
        }
        pemParser.close();
        JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider(BouncyCastleProvider.PROVIDER_NAME);
        return converter.getPrivateKey(privateKeyInfo);
    }

But we cannot use bouncycastle bckpix.jar as its having conflict with bcfips.jar as NoSuchField error. Is there any alternate to bouncycastle for do this task ?

This is a sample private key Encrypted using passphrase = "520759"

Michael Fehr · Answer 1 · 2021-09-03T08:26:37.360

Yes, you can do use an encrypted RSA private key without BouncyCastle, but it's a little bit "tricky".

This is the typical structure of an encrypted RSA key created with nowadays OpenSSL (version >= 1.1.1):

SEQUENCE (2 elem)
  SEQUENCE (2 elem)
    OBJECT IDENTIFIER 1.2.840.113549.1.5.13 pkcs5PBES2 (PKCS #5 v2.0)
    SEQUENCE (2 elem)
      SEQUENCE (2 elem)
        OBJECT IDENTIFIER 1.2.840.113549.1.5.12 pkcs5PBKDF2 (PKCS #5 v2.0)
        SEQUENCE (3 elem)
          OCTET STRING (8 byte) 528FDA1DBEFFE635
          INTEGER 2048
          SEQUENCE (2 elem)
            OBJECT IDENTIFIER 1.2.840.113549.2.9 hmacWithSHA256 (RSADSI digestAlgorithm)
            NULL
      SEQUENCE (2 elem)
        OBJECT IDENTIFIER 2.16.840.1.101.3.4.1.42 aes256-CBC (NIST Algorithm)
        OCTET STRING (16 byte) 9BA62A9EA65CB20CDF39BAEE7262AA45
  OCTET STRING (1232 byte) 8AAFCB6BF8D877804A3E81DB996526334E5AF4F97638C388083B045B2E3A132AD749…

The "real" key is the data in the very last "OCTET STRING" (1232 byte), but it is the encrypted data. The encryption itself is defined by the data above: it is the new encryption scheme pkcs5PBES2 (PKCS #5 v2.0) that uses PBKDF2 for the key derivation with an algorithm hmacWithSHA256. The salt for the key derivation is in the 8 byte long OCTET STRING "528FDA1DBEFFE635".

Edit: for PBKDF2 you need the number of iterations - you find this value in "INTEGER 2048" (2048).

Now we have the key, let's start the encryption using the AES algorithm in mode CBC (aes256-CBC). The randomly generated initialization vector for this task is in the "OCTET STRING" (16 byte): "9BA62A9EA65CB20CDF39BAEE7262AA45".

To get these values programmatically, you have two choices:

use an ASN1 parser (smart way) -or-
search for the identifier and get the data fields around (rough way).

In the end, it is a simple decryption of the data, and you get a PKCS#8 encoded byte array as input for a "PKCS8EncodedKeySpec" that will "generate" your RSA private key.

For learning purposes I have gone the rough way, and it worked... but as there are some more encryption schemes, key derivations and key encryption algorithms my solution was only good for exact the encryption parameter shown above.

Tried many solutions nothing works , I Updated the question with the private key I need to decrypt. This is thread is the closest i reached , https://stackoverflow.com/questions/63832456/parsing-encrypted-pkcs8-encoded-pem-file-programatically Followed the accepted answer by you. But no luck , getting error cipher.init(Cipher.DECRYPT_MODE, secretKey, ivParameterSpec); If you have any Java Code which can decrypt the Key Shared above , pls share , Thanks — Chanky Mallick, Sep 14 '21 at 19:51

BouncyCastle Alternative to Decrypt a Encrypted p8 file

1 Answers1