What Is the Cost for an Attacker to Execute a Persistent Transaction Spam Attack?

The cost for an attacker to execute a persistent transaction spam attack is the cumulative sum of all the transaction fees they must pay for the spam transactions to be confirmed. Since miners prioritize transactions by fee-per-byte, the attacker must pay a competitive fee for every spam transaction to ensure it is included and clogs the block space.

In a congested network, this cost can quickly become prohibitively expensive, as the attacker is essentially paying the market price for all the block space they consume. This economic barrier is the primary defense against such attacks.