[FEATURE-REQ] SHA256 of geohashes in the intersection code

[tremblerz]

Issue type

This builds on top of #806. This is going to be a change that we need to apply to the intersect logic. See the old PR for reference - relevant file diff from the PR
When we load the location data from the Asyncstorage, instead of reading the raw data, we need to read from Geohashes. The next step is as follows -

1. read geohashes
2. Append timestamp to the geohash
3. Apply SHA256([geohash, timestamp])
4. Compare it with the received points in the intersect.js

[diarmidmackenzie]

My view is that these should use a slow hash algorithm, and scrypt is my favoured approach for various reasons detailed here:

https://pathcheck.atlassian.net/wiki/spaces/TEST/pages/61112371/Design+for+MVP1+HA+JSON+Changes

[summetj]

@tremblerz - If I'm reading your issue description correctly, #806 is the first step in this process that can be done independently, and this can be added only after #806 is finished. Did I understand that correctly?

[diarmidmackenzie]

For anyone who wants to work on tis please see Jira SAF-268 for a proposed alternate plan of attack.

Same basic outcome, but proposing different sequencing to ensure Safe Paths & Safe Places retain compatibility as much as possible during this change.

[yonatanmk]

To clarify, we're going to hash the concatenation of the geohash and timestamp using Scrypt, not SHA256