Unique transaction fees may reveal specific users or wallets or wallet versions which reduces privacy for those specific users and the rest of the network.
New ZIPs with flexible fees, such as [#ian-1]_, along with scaling solutions need to be evaluated and applied.
Denial Of Service Vulnerability
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A transaction-rate-based denial of service attack occurs when an attacker generates enough transactions over a window of time to prevent legitimate transactions from being mined, or to hinder syncing blocks for full nodes or miners.
There are two primary protections to this kind of attack in Zcash: the block size limit, and variable transaction fees. The block size limit ensures that full nodes and miners can sync blocks even if they are completely full. However it does not protect users sending legitimate transactions to have their transactions confirmed in a timely manner.
Variable fees can mitigate this kind of denial of service because in there are more transactions available than can fit into a single block, a miner is assumed to choose the transactions that pay the highest fees. If legitimate wallets increase their fees during this condition, the attacker must also increase the fees of their transactions. This imposes a growing and ongoing cost to the attacker which limits the time window they can continue the attack.
This proposal does not alter how fees are paid from transactions to miners. However, it does require wallets to use a fixed flat fee. Therefore during a transaction rate DoS attack, legitimate fees may not rise, so an attacker can extend an attacker for a longer window for the same cost.
This ZIP does not address this concern. A future ZIP should address this issue for shielded wallets.
* The new default fee of 0.00001 or 1000 zats must start activation at block 1,080,000
* With a grace period of ~4 weeks (block 1,120,000) to upgrade to the reduced default transaction fee for zcashd and core clients used by exchanges & service providers.
Zbay, Zecwallet Suite(Zecwallet Lite for Desktop/iOS/Android & Zecwallet FullNode) and Nighthawk Wallet Android & iOS have agreed to implement the reduced fees.
Additionally, all wallet developers and operators should monitor the Zcash network for rapid growth in transaction rates. As we tend toward fuller blocks, we should proactively address the issue of growing mempool in a separate follow up ZIP.