Java - Encrypting with RSA key

Question

I've been fighting with this issue for a while now. The matter is that I have to send a PEM string to a server, which expects the final step of the following:

An encryption key of type 3DES o AES-256.
That key, encrypted with an RSA key.
That output, encoded in Base64 and in PEM format.

Here's what I got so far:

Based on the RSA key I've got from the server, I create a Cipher:

 Cipher rsa = Cipher.getInstance("RSA");

 rsa.init(Cipher.ENCRYPT_MODE, (RSAPublicKey) obj);

Later, I create an AES key:

//IV. 
byte[] bytes = new byte[16];
SecureRandom random = new SecureRandom();
random.nextBytes(bytes);

Map<String, byte[]> aes = new HashMap<String, byte[]>();

aes.put("IV", ConversionUtil.toHex(bytes, 8).getBytes());

KeyGenerator keyGen = KeyGenerator.getInstance("AES");

keyGen.init(256);
Key encryptionKey = keyGen.generateKey();

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); 

cipher.init(Cipher.ENCRYPT_MODE, encryptionKey, new IvParameterSpec(ConversionUtil.toHex(bytes, 8).getBytes()));

aes.put("key", cipher.doFinal(encryptionKey.getEncoded()));

Use all that to create the PEM string:

            StringBuilder sb = new StringBuilder();
            sb.append(StringUtils.repeat("-", 5));
            sb.append("BEGIN PEM file");
            sb.append(StringUtils.repeat("-", 5));
            sb.append("\n");

            sb.append("Proc-Type: 4,ENCRYPTED\n");
            sb.append("DEK-Info: " + "AES-256-CBC" + "," + new String(aes.get("IV")) + "\n");
            sb.append("");
            sb.append(Base64.encode(rsa.doFinal(aes.get("key"))));

            sb.append("\n");
            sb.append(StringUtils.repeat("-", 5));
            sb.append("END PEM file");
            sb.append(StringUtils.repeat("-", 5));

And then send that out to the server, which throws the following error:

3936:error:0906D06C:PEM routines:PEM_read_bio:no start line:.\crypto\pem\pem_lib.c:698:

I don't have much more visibility of the error, but I wanted to check if there's anything wrong I might be doing in the process, as it seems that error is associated to the unrecognition of the PEM.

Let me know if you have any questions.

Thanks!

You are supposed to encrypt using RSA and you are encrypting key using AES — Amit Deshpande
– Amit Deshpande, Commented Dec 5, 2012 at 17:54
Mmm, you might be right, I'm now trying to provide the IV to the RSA Cipher, but I'm getting this error: cipher.init(Cipher.ENCRYPT_MODE, (RSAPublicKey) obj, new IvParameterSpec(iv)); java.security.InvalidAlgorithmParameterException: Parameters not supported — bassprodukt
– bassprodukt, Commented Dec 5, 2012 at 18:05
Yup, I do have that, but I also need to provide an IV since the server will be using it along the RSA key it provides to decrypt the AES/3DES key I made. — bassprodukt
– bassprodukt, Commented Dec 5, 2012 at 18:13
This is not the way to provide IV. IV don't need encryption it can be shared publicly also — Amit Deshpande
– Amit Deshpande, Commented Dec 5, 2012 at 18:19

Maarten Bodewes · Accepted Answer · 2012-12-05 21:34:56Z

2

The specific error is reported because there should be no spaces between the dashes and the BEGIN statement. I don't know about the other issues, but it seems you have some work ahead of you to match the exact input requirements. Make sure you understand precisely what is expected, or you may have to try different formats "ad nauseam".

answered Dec 5, 2012 at 21:34

Maarten Bodewes

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2 Comments

bassprodukt Over a year ago

You just hit the nail. I've managed to make some advances on this, I'm now fighting against the expected carriage returns. Is there any way I can manually insert these without regards of the actual system configuration? As I'm currently trying with \n and \r, but on the actual output, there are extra ones I didn't insert. I understand the system has some influence onto how the \n and \r are made.

Maarten Bodewes Over a year ago

The system should not insert carriage returns/line feeds. It's more likely that something is going wrong in your application code. Keep debugging, you will get there eventually :)

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