CODEWITHSUNDEEP
javaandroidrsapem
cph2117
cph2117

Reputation: 2681

PEM to PublicKey in Android

I've seen a number of similar questions, but nothing has quite worked for me. I am simply trying to convert an RSA public key that's in PEM format that I've retrieved from a server into a PublicKeyin Android. Can anyone point me in the right direction?

EDIT: I've successfully used the following code to convert the PEM into a PublicKey, but upon encoding a message, I get unexpected output...

 public PublicKey getFromString(String keystr) throws Exception
    {
        // Remove the first and last lines

        String pubKeyPEM = keystr.replace("-----BEGIN PUBLIC KEY-----\n", "");
        pubKeyPEM = pubKeyPEM.replace("-----END PUBLIC KEY-----", "");

        // Base64 decode the data

        byte [] encoded = Base64.decode(pubKeyPEM);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        PublicKey pubkey = kf.generatePublic(keySpec);

        return pubkey;
    }

    public String RSAEncrypt(final String plain) throws NoSuchAlgorithmException, NoSuchPaddingException,
            InvalidKeyException, IllegalBlockSizeException, BadPaddingException, IOException {

        if (pubKey!=null) {
            cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, pubKey);
            encryptedBytes = cipher.doFinal(plain.getBytes());
            Log.d("BYTES", new String(encryptedBytes));
            return Hex.encodeHexString(encryptedBytes);
        }
        else
            return null;
    }

The output looks like this:

b6813f8791d67c0fa82890d005c8ff554b57143b752b34784ad271ec01bfaa9a6a31e7ae08444baef1585a6f78f3f848eecb1706bf7b2868fccefc9d728c30480f3aabc9ac5c3a9b4b3c74c2f7d6f0da235234953ea24b644112e04a2ec619f6bf95306ef30563c4608ec4b53ed7c15736d5f79c7fa1e35f2444beb366ae4c71

when I expect something closer to:

JfoSJGo1qELUbpzH8d4QXtafup+J2F9wLxHCop00BQ4YS0cRdRCKDfHpFPZQYjNeyQj00HwHbz+vj8haTPbpdqT94AHAl+VZ+TPAiUw1U5EXLLyy4tzbmfVI7CwvMm26lwB4REzYUZdedha1caxMEfxQ5duB+x4ol9eRZM/savg=

Is there some formatting or file type that I'm missing?

Upvotes: 13

Views: 10196

Answers (2)

Daniel C
Daniel C

Reputation: 2480

This doesn't answer the question, but I find the content relevant. Posting as an answer because it doesn't fit as a comment.

PEM vs DER

  • PEM basically encapsulates a DER-encoded certificate or key.
  • DER is binary, PEM is text; so PEM can easily be copy-pasted to an email, for example.
  • What PEM does is:
    1. Encode the DER certificate or key using Base64, and
    2. Delimit the result with -----BEGIN <something>----- and -----END <something>-----.
  • The key or certificate is the same, just represented in a different format.

Mostly paraphrasing from ASN.1(wiki).

DER to Android/Java public key

The following is an example of how to use a key factory in order to instantiate a DSA public key from its encoding. Assume Alice has received a digital signature from Bob. Bob also sent her his public key (in encoded format) to verify his signature. Alice then performs the following actions:

X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(bobEncodedPubKey);
KeyFactory keyFactory = KeyFactory.getInstance("DSA");
PublicKey bobPubKey = keyFactory.generatePublic(bobPubKeySpec);

...

Note that bobEncodedPubKey is DER-encoded in this sample.

https://developer.android.com/reference/java/security/KeyFactory

PEM to Android/Java public key

Similar to what is done for DER, but do the following beforehand:

  1. Remove the BEGIN/END delimitation, and
  2. Decode the content in Base64 to obtain the original DER.

(The question already shows code on how to do this.)

Upvotes: 4

cph2117
cph2117

Reputation: 2681

To answer my own question...The first output is in hex and the second output is in base 64. Just change the return statement to return new String(Base64.encode(encryptedBytes)); and you'll be good!

Upvotes: 8

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