[Bug]: Missing length check when parsing SignatureShareRequest

[djordon]

Bug - Missing length check when parsing SignatureShareRequest

1. Description

We do not check the length of the contents of SignatureShareRequests. This can lead to resource exhaustion of the signer, since a malicious coordinator can jam up the system by broadcasting signature share requests with lots of junk. What's more, going through the SignatureShareRequest takes a lot more time than generating the request itself, so doing basic validation is crucial here.

1.1 Context & Purpose

We do not want to make it easy for a malicious signer to lock the protocol. Doing basic validation on the request is necessary to ensure that an attacker cannot compromise the protocol.

2. Technical Details:

There is a ticket for this in WSTS at Trust-Machines/wsts#108. The fix in this repo is to update to use it.

2.1 Acceptance Criteria:

• A malicious signer cannot exhaust other signer resources by sending bad SignatureShareRequest messages.

3. Related Issues and Pull Requests (optional):