Walrus assurance and security properties

The properties below hold true subject to the assumption that for all storage epochs 2/3 of shards are operated by storage nodes that faithfully and correctly follow the Walrus protocol.

As described before, each blob is encoded into slivers using an erasure code and a blob ID is cryptographically derived. For a given blob ID there is a point of availability (PoA) and an availability period, observable through an event on the Sui chain.

The following properties relate to the PoA:

• After the PoA, for a blob ID, any correct user that performs a read within the availability period will eventually terminate and get a value (V) which is either the blob contents (F) or None.
• After the PoA, if two correct users perform a read and get (V) and (V'), respectively, then (V = V').
• A correct user with an appropriate storage resource can always perform store for a blob (F) with a blob ID and advance the protocol until the PoA.
• A read after the PoA for a blob (F) stored by a correct user, will result in (F).

Some assurance properties ensure the correct internal processes of Walrus storage nodes. For the purposes of defining these, an inconsistency proof proves that a blob ID was stored by a user that incorrectly encoded a blob.

• After the PoA and for a blob ID stored by a correct user, a storage node is always able to recover the correct slivers for its shards for this blob ID.
• After the PoA, if a correct storage node cannot recover a sliver, it can produce an inconsistency proof for the blob ID.
• If a blob ID is stored by a correct user, an inconsistently proof cannot be derived for it.
• A read by a correct user for a blob ID for which an inconsistency proof may exist returns None.

Note that there is no delete operation and a blob ID past the PoA will be available for the full availability period.