added revocation certificate task

Google-Summer-of-Code-2016.md

@@ -267,3 +267,39 @@ dialog.
 **Contact:** [Mailinglist](https://lists.riseup.net/www/subscribe/openkeychain)
 or on IRC (Valodim in [#openkeychain at
 irc.freenode.net](https://kiwiirc.com/client/irc.freenode.net/openkeychain))
+
+
+## Revocation Certificates
+**Brief explanation:** Revocation certificates are used to revoke a key
+even if the secret key is no longer accessible (either the actual key has
+been lost or its password forgotten), and is usually the last recourse in
+such cases. This task would involve allowing OpenKeychain to both generate
+and use revocation certificates.
+
+The two components:
+1. Creation: Allowing users to create a revocation certificate for a given key
+from within OpenKeychain (this would involve saving the revoked public key).
+2. Application: Revocation certificates come in two forms - as a revoked public key,
+and much less frequently, as a detached revocation signature. In the case of
+the latter the certificate must first be applied to the correct public key before
+proceeding. In either case, the revoked key must be uploaded to keyservers to 
+complete the revocation process. The revocation and upload should be atomic.
+
+This is a smaller task which we expect to take only one or two weeks, which
+makes it suitable as a secondary goal and providing a change of pace for some
+time while working on another task.
+
+**Expected results:** Support for detached signatures in the Encrypt/Decrypt
+dialog.
+
+**Priority:** low
+
+**Knowledge Prerequisite:** Java programming
+
+**Skill level:** low
+
+**Mentor:** Vincent Breitmoser
+
+**Contact:** [Mailinglist](https://lists.riseup.net/www/subscribe/openkeychain)
+or on IRC (Valodim in [#openkeychain at
+irc.freenode.net](https://kiwiirc.com/client/irc.freenode.net/openkeychain))