Use SHA2 instead of MD5

[breezewish]

Currently we are using MD5 to store files, which is VERY insecure since a MD5 collision can be generated in minutes on personal PC even several years ago.

Since SHA1 is also considered insecure these years, we need to migrate to SHA2, for example SHA256.

Upgrade to existing data is required.

[twd2]

@mongodb

[breezewish]

@twd2 MongoDB's MD5 is not intended to be used to deduplicate as what we are doing now. It is a checksum for file system integrity only, for detecting data corruption.

Ref:

https://docs.mongodb.com/manual/reference/glossary/#term-checksum https://docs.mongodb.com/manual/reference/glossary/#term-md5

[ksyx]

Updating users' data will be a big project...