How Does the Concept of “Data Availability” Relate to the Security of All Layer 2 Solutions?

Data availability (DA) is the guarantee that the raw transaction data for a batch posted to L1 is accessible to all users. This is crucial because, without access to the data, users cannot reconstruct the L2 state to verify the proof (fraud or validity) or withdraw their funds.

If the sequencer withholds the data, the L2 is effectively frozen and insecure. L2s rely on L1 to ensure this data is published.