Assuming the client supports different keys, what is some rationale that should be considered for signing and encryption keys?
The encryption key
- needs to be present on each device that is used to read email
- all those copies means it has a greater risk of getting lost or stolen on mobile devices (and therefore should be revoked)
The signing key
- can be device-specific
- Since it has a long lasting lifetime (2-4 years), it can be revoked when a device is stolen.
Therefore a fewer subset of messages will have their integrity called into question
Is this valid thinking? What are some other perspectives?