PEM to PublicKey in Android

Question

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

Answer 1

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 ----- and -----END -----.
• 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.)