compression

Compression for ERC-4337

Contracts implementing compression for ERC-4337 accountss. This work is compatible with ERC-4337 v0.6.

See https://hackmd.io/@voltrevo/Bkz8syuUp for more details & performance.

Performance

Marginal Calldata for an ERC20 Transfer

Strategy	Zeros	Non-Zeros	Bytes	L1 Gas
Vanilla 4337	421	155	576	4164
Compressed 4337	0	27	27	432

Note that L1 Gas is calculated as 4*zeros + 16*nonZeros. The exact value depends on your L2 of choice. This may involve an additional compression layer, but today this generally does not take compressibility into account, so the savings ratio should still be approximately correct.

The size of ETH transfers and other ERC20 operations is similar. Calls to other contracts need to add the size of their tx.data field, but still benefit from compression of tx.to and tx.value and a compact representation of tx.data (avoid 32 bytes to represent length and 15.5 bytes for zero padding).

The full calldata cost is expected to include a share of the approximately 174 bytes of overhead the bundle needs to pay for. This includes the aggregated BLS signature (64 bytes) and the non-data fields of the top-level ECDSA transaction (approx. 109 bytes).

Assuming this cost is divided equally, an ERC20 transfer would then need to cover the following numbers of bytes:

Bundle Size	Bytes
1	201
2	114
5	62
20	36
100	29

The L2 gas overhead for doing the decompression to make this possible is about 57,000. This means compression should break even on chains where L2 gas is about 15x cheaper than L1 gas, and provide savings thereafter. (TODO: Do this paragraph more thoroughly and document it.)

Requirements

• The bundler needs to use HandleAggregatedOpsCaller (or something better) (including the off-chain compression needed to call it correctly)
• The account (aka SCW) needs to decompress its userOp.calldata field similar to DemoAccount (see fallback)
• Your 4337 wallet (end-user software) needs to correctly compress userOp.calldata off-chain
• Your 4337 wallet should round up these userOp fields to 3 significant figures: callGasLimit, verificationGasLimit, preVerificationGas, maxFeePerGas, maxPriorityFeePerGas (additional significant figures are supported but require extra bytes)
• Addresses used should be registered in the AddressRegistry. Unregistered addresses cost 20 bytes instead of just 3. Registration is a one-time cost.

Bundlers set the actual fees for 4337 wallets. You can see how much a bundler requires using eth_estimateUserOperationGas.