We've made some significant changes to BIP75 which we think simplify things greatly:

Instead of introducing encrypted versions of all BIP70 messages (EncryptedPaymentRequest, EncryptedPayment, etc), we have defined a generic EncryptedProtocolMessage type which is essentially a wrapper that enables encryption for all existing BIP70 messages. This reduces the number of new messages we are defining and makes it easier to add new message types in the future.

We've also decided to use AES-GCM instead of AES-CBC, which eliminates the need for the verification hash.

A pull request has been submitted, which can be seen here: https://github.com/bitcoin/bips/pull/385

All comments are welcome. Thank you!

James