[CAY-2109] cayenne-crypto: add value authentication (HMAC)

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.B1
• Assignee: Nikita Timofeev
• Reporter: Andrus Adamchik
• Created: 30/Aug/16 08:55
• Updated: 31/Mar/17 13:08
• Resolved: 31/Mar/17 13:08

Description

A previously ignored concern with using cayenne-crypto is data integrity. Corrupt messages will happily decrypt to garbage. Valid messages will happily decrypt with a corrupt key, also to garbage. So to make the system more robust, we'll be adding an optional message authentication code (MAC). I am using "Cryptography Engineering" book [1] as a reference on the best MAC practices. Implementation parameters:

• HMAC [2]
• SHA-256
• authenticate-then-encrypt
• Authenticated message will be made of the following fields:

protocol_version || flags || secret_key || message

(or should we just do header || secret_key || message?)

[1] https://www.schneier.com/books/cryptography_engineering/
[2] https://en.wikipedia.org/wiki/Hash-based_message_authentication_code