Support for EME-OAEP encoding from PKCS#1 v2.1

[fweissberg]

(This is the issue corresponding to https://github.com/randombit/botan/pull/1383) In the future, Botan should support EME-OAEP encoding as specified in PKCS#1 v2.1 (RFC 3447). https://tools.ietf.org/html/rfc3447#section-7.1

[lieser]

Although the algorithm description in both RFCs is different, the end result should be the same (see also https://crypto.stackexchange.com/questions/40032/why-did-oaep-change-from-pkcs1-v2-0-and-v2-1). The main reason for the changes in the algorithm seems to be to fix possible side channels.

So this issue can be closed.

One think to keep in mind if using OAEP in the context of TPM 2.0, is that the TMP 2.0 specification mandates that if a label is provided, it must end with a null byte.