Export public key for external usage

[hatemalimam]

When exporting a key from the iPhone keychain, it's exported in a cut down format – just the public key and exponent without any of the other ASN.1 stuff we’d expect in a fully encoded public key. The java crypto functions generally expect a fully encoded key (OID and all).

Any easy way to include such helpers that play well with this lib ?

an example of the helpers can be found here https://github.com/reejosamuel/RSA/blob/master/RSA/RSA/RSA.m#L121

[amitaymolko]

The code you've provided looks helpful and will help implement this quickly. I'll look into this when I get the time If you happen to get around to fixing this and creating a PR that would also be great. Thanks