size-solidity

Size is a credit marketplace with unified liquidity across maturities.

Networks:

Audits

For bug reports, please refer to our Bug Bounty Program

Documentation

Overview, Accounting and Protocol Design

Whitepaper

Technical overview

Architecture

The architecture of Size v2 was inspired by dYdX v2, with the following design goals:

Upgradeability
Modularity
Overcome EIP-170's contract code size limit of 24kb
Maintaining the protocol invariants after each user interaction ("FREI-PI" pattern)

For that purpose, the contract is deployed behind an UUPS-Upgradeable proxy, and contains a single entrypoint, Size.sol. External libraries are used, and a single State storage variable is passed to them via delegatecalls. All user-facing functions have the same pattern:

state.validateFunction(params);
state.executeFunction(params);
state.validateInvariant(params);

The Multicall pattern is also available to allow users to perform a sequence of multiple actions, such as depositing borrow tokens, liquidating an underwater borrower, and withdrawing all liquidated collateral. Note: in order to accept ether deposits through multicalls, all user-facing functions have the payable modifier, and deposit always uses address(this).balance to wrap ether. This means leftover amounts, if sent forcibly, are always credited to the depositor.

Additional safety features were employed, such as different levels of Access Control (ADMIN, PAUSER_ROLE, KEEPER_ROLE, BORROW_RATE_UPDATER_ROLE), and Pause.

Tokens

In order to address donation and reentrancy attacks, the following measures were adopted:

No withdraws of native ether, only wrapped ether (WETH)
Underlying borrow and collateral tokens, such as USDC and WETH, are converted 1:1 into deposit tokens via deposit, which mints szaUSDC and szWETH, and received back via withdraw, which burns deposit tokens 1:1 in exchange for the underlying tokens.

Maths

All mathematical operations are implemented with explicit rounding (mulDivUp or mulDivDown) using Solady's FixedPointMathLib. Whenever a taker-maker operation occurs, all rounding tries to favor the maker, who is the passive party. In some generic situations, such as in yield curve calculations, the rounding is always in one direction.

Decimal amounts are preserved until a conversion is necessary:

USDC/aUSDC: 6 decimals
WETH/szETH: 18 decimals
szDebt: same as borrow token
Price feeds: 18 decimals

All percentages are expressed in 18 decimals. For example, a 150% liquidation collateral ratio is represented as 1500000000000000000.

Oracles

Price Feed

A contract that provides the price of ETH in terms of USDC in 18 decimals. For example, a price of 3327.39 ETH/USDC is represented as 3327390000000000000000.

Variable Pool Borrow Rate Feed

In order to set the current market average value of USDC variable borrow rates, we perform an off-chain calculation on Aave's rate, convert it to 18 decimals, and store it in the Size contract. For example, a rate of 2.49% on Aave v3 is represented as 24900000000000000. The admin can disable this feature by setting the stale interval to zero. If the oracle information is stale, orders relying on the variable rate feed cannot be matched.

Copy trading

Since Size v1.6.1, users can copy other users' limit orders.

Users can copy borrow/loan offers from other users
Users can copy both or a single offer from a single address
Users can specify safeguards per copied curve:
- min/max APR (safety envelope): if the calculated APR falls outside of this range, the min/max is used instead
- min/max tenor: if the requested tenor goes outside of this range, the market order reverts
Users can specify offset APRs to be applied to the curves
Once a copy offer is set, the user's own offers should be ignored, even if they update them. Copy offers have precedence until erased (setting them to null/default vales)

As an additional safety measure against inverted curves, market orders check that the borrow offer is lower than the user's loan offer for a given tenor. This does not prevent the copy address from changing curves in a single multicall transaction and bypassing this check.

Notes

Copying another account's limit orders introduces the risk of them placing suboptimal rates and executing market orders against delegators, incurring monetary losses. Only trusted addresses should be copied.
The max/min params from the copyLimitOrder method are not global max/min for the user-defined limit orders; they are specific to copy offers. Once the copy address offer is no longer valid, max/min guards for mismatched curves will not be applied. The only reason to stop market orders is in the event of "self arbitrage," i.e., for a given tenor, when the borrow curve >= lending curve, since these users could be drained by an attacker by borrowing high and lending low in a single transaction.

Test

forge install
forge test

Coverage

yarn coverage

FIles

| File                                                                 | % Lines            | % Statements       | % Branches       | % Funcs          |
+======================================================================================================================================================+
| src/Size.sol                                                         | 100.00% (85/85)    | 100.00% (67/67)    | 100.00% (3/3)    | 100.00% (23/23)  |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/SizeView.sol                                                     | 100.00% (49/49)    | 100.00% (45/45)    | 100.00% (1/1)    | 100.00% (23/23)  |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/AccountingLibrary.sol                                  | 96.81% (91/94)     | 96.88% (93/96)     | 86.96% (20/23)   | 100.00% (12/12)  |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/CapsLibrary.sol                                        | 93.33% (14/15)     | 93.33% (14/15)     | 75.00% (3/4)     | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/DepositTokenLibrary.sol                                | 100.00% (14/14)    | 100.00% (10/10)    | 100.00% (0/0)    | 100.00% (4/4)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/LoanLibrary.sol                                        | 97.44% (38/39)     | 97.83% (45/46)     | 93.33% (14/15)   | 100.00% (8/8)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/Math.sol                                               | 100.00% (23/23)    | 100.00% (25/25)    | 100.00% (5/5)    | 100.00% (6/6)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/Multicall.sol                                          | 100.00% (11/11)    | 100.00% (16/16)    | 100.00% (0/0)    | 100.00% (1/1)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/OfferLibrary.sol                                       | 100.00% (52/52)    | 100.00% (67/67)    | 100.00% (14/14)  | 100.00% (10/10)  |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/RiskLibrary.sol                                        | 97.06% (33/34)     | 97.83% (45/46)     | 83.33% (5/6)     | 100.00% (9/9)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/YieldCurveLibrary.sol                                  | 92.31% (36/39)     | 96.49% (55/57)     | 86.67% (13/15)   | 100.00% (4/4)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/BuyCreditLimit.sol                             | 100.00% (7/7)      | 100.00% (5/5)      | 100.00% (1/1)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/BuyCreditMarket.sol                            | 100.00% (56/56)    | 100.00% (65/65)    | 100.00% (16/16)  | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Claim.sol                                      | 100.00% (13/13)    | 100.00% (16/16)    | 100.00% (2/2)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Compensate.sol                                 | 100.00% (50/50)    | 100.00% (53/53)    | 100.00% (13/13)  | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/CopyLimitOrders.sol                            | 100.00% (24/24)    | 100.00% (21/21)    | 100.00% (11/11)  | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Deposit.sol                                    | 100.00% (25/25)    | 100.00% (24/24)    | 100.00% (8/8)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Initialize.sol                                 | 100.00% (82/82)    | 100.00% (73/73)    | 100.00% (18/18)  | 100.00% (11/11)  |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Liquidate.sol                                  | 100.00% (32/32)    | 100.00% (38/38)    | 100.00% (5/5)    | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/LiquidateWithReplacement.sol                   | 100.00% (35/35)    | 100.00% (43/43)    | 100.00% (5/5)    | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Repay.sol                                      | 100.00% (11/11)    | 100.00% (11/11)    | 100.00% (2/2)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/SelfLiquidate.sol                              | 100.00% (14/14)    | 100.00% (17/17)    | 100.00% (2/2)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/SellCreditLimit.sol                            | 100.00% (7/7)      | 100.00% (5/5)      | 100.00% (1/1)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/SellCreditMarket.sol                           | 100.00% (50/50)    | 100.00% (56/56)    | 100.00% (15/15)  | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/SetUserConfiguration.sol                       | 100.00% (16/16)    | 100.00% (21/21)    | 100.00% (2/2)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/UpdateConfig.sol                               | 100.00% (53/53)    | 100.00% (51/51)    | 100.00% (32/32)  | 100.00% (5/5)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/libraries/actions/Withdraw.sol                                   | 100.00% (20/20)    | 100.00% (18/18)    | 100.00% (7/7)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.1/PriceFeed.sol                                      | 100.00% (18/18)    | 100.00% (20/20)    | 100.00% (0/0)    | 100.00% (6/6)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.1/adapters/ChainlinkPriceFeed.sol                    | 100.00% (25/25)    | 100.00% (39/39)    | 100.00% (9/9)    | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.1/adapters/ChainlinkSequencerUptimeFeed.sol          | 100.00% (9/9)      | 100.00% (11/11)    | 100.00% (3/3)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.1/adapters/UniswapV3PriceFeed.sol                    | 100.00% (29/29)    | 100.00% (40/40)    | 100.00% (5/5)    | 100.00% (2/2)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.2/PriceFeedChainlinkUniswapV3TWAPx2.sol              | 0.00% (0/13)       | 0.00% (0/17)       | 100.00% (0/0)    | 0.00% (0/3)      |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.2/PriceFeedUniswapV3TWAPChainlink.sol                | 100.00% (11/11)    | 100.00% (12/12)    | 100.00% (0/0)    | 100.00% (3/3)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/oracle/v1.5.3/PriceFeedUniswapV3TWAP.sol                         | 0.00% (0/8)        | 0.00% (0/7)        | 100.00% (0/0)    | 0.00% (0/3)      |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/token/NonTransferrableToken.sol                                  | 100.00% (19/19)    | 100.00% (13/13)    | 100.00% (1/1)    | 100.00% (8/8)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/v1.5/SizeFactory.sol                                             | 97.37% (111/114)   | 98.99% (98/99)     | 90.00% (9/10)    | 96.97% (32/33)   |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/v1.5/libraries/MarketFactoryLibrary.sol                          | 100.00% (3/3)      | 100.00% (3/3)      | 100.00% (0/0)    | 100.00% (1/1)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/v1.5/libraries/NonTransferrableScaledTokenV1_5FactoryLibrary.sol | 100.00% (2/2)      | 100.00% (1/1)      | 100.00% (0/0)    | 100.00% (1/1)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/v1.5/libraries/PriceFeedFactoryLibrary.sol                       | 100.00% (2/2)      | 100.00% (1/1)      | 100.00% (0/0)    | 100.00% (1/1)    |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| src/v1.5/token/NonTransferrableScaledTokenV1_5.sol                   | 87.78% (79/90)     | 90.80% (79/87)     | 25.00% (2/8)     | 85.00% (17/20)   |
|----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------|
| Total                                                                | 96.60% (1249/1293) | 96.98% (1316/1357) | 94.27% (247/262) | 95.78% (227/237) |
╰----------------------------------------------------------------------+--------------------+--------------------+------------------+------------------╯

Tests per file

┌─────────────────────────────────┬────────┐
│ (index)                         │ Values │
├─────────────────────────────────┼────────┤
│ BuyCreditLimit                  │ 4      │
│ BuyCreditMarket                 │ 10     │
│ ChainlinkPriceFeed              │ 8      │
│ ChainlinkSequencerUptimeFeed    │ 2      │
│ Claim                           │ 10     │
│ Compensate                      │ 20     │
│ CopyLimitOrders                 │ 16     │
│ CryticToFoundry                 │ 27     │
│ Deposit                         │ 5      │
│ GenericMarket                   │ 20     │
│ Initialize                      │ 4      │
│ LiquidateWithReplacement        │ 6      │
│ Liquidate                       │ 12     │
│ Math                            │ 6      │
│ Multicall                       │ 9      │
│ NonTransferrableScaledTokenV1   │ 17     │
│ NonTransferrableToken           │ 8      │
│ OfferLibrary                    │ 1      │
│ Pause                           │ 2      │
│ PriceFeedUniswapV3TWAPChainlink │ 3      │
│ PriceFeed                       │ 9      │
│ Repay                           │ 7      │
│ SelfLiquidate                   │ 10     │
│ SellCreditLimit                 │ 5      │
│ SellCreditMarket                │ 13     │
│ SetUserConfiguration            │ 3      │
│ SizeFactory                     │ 36     │
│ SizeView                        │ 5      │
│ SwapData                        │ 3      │
│ UniswapV3PriceFeed              │ 5      │
│ UpdateConfig                    │ 7      │
│ Upgrade                         │ 2      │
│ Withdraw                        │ 9      │
│ YieldCurve                      │ 14     │
└─────────────────────────────────┴────────┘

Protocol invariants

Invariants implemented

Check PropertiesSpecifications.sol

Run Echidna with

yarn echidna-property
yarn echidna-assertion

Onchain fuzzing

source .env
FOUNDRY_PROFILE=fork FOUNDRY_INVARIANT_RUNS=0 FOUNDRY_INVARIANT_DEPTH=0 forge test --mc FoundryForkTester -vvvvv --ffi

Check the coverage report with

yarn echidna-coverage

Formal Verification

Math.binarySearch

Run Halmos with

for i in {0..5}; do halmos --loop $i; done

Known limitations

The protocol does not support rebasing/fee-on-transfer tokens
The protocol only supports tokens compliant with the IERC20Metadata interface
The protocol only supports pre-vetted tokens
The protocol owner, KEEPER_ROLE, PAUSER_ROLE, and BORROW_RATE_UPDATER_ROLE are trusted
The protocol uses Uniswap TWAP as a fallback oracle in case Chainlink is stale.
In case Chainlink reports a wrong price, the protocol state cannot be guaranteed. This may cause incorrect liquidations, among other issues
In case the protocol is paused, the price of the collateral may change during the unpause event. This may cause unforseen liquidations, among other issues
It is not possible to pause individual functions. Nevertheless, BORROW_RATE_UPDATER_ROLE and admin functions are enabled even if the protocol is paused
Users blacklisted by underlying tokens (e.g. USDC) may be unable to withdraw
If the Variable Pool (Aave v3) fails to supply or withdraw for any reason, such as supply caps, Size's deposit and withdraw may be prevented
Centralization risk related to integrations (USDC, Aave v3, Chainlink) are out of scope
The Variable Pool Borrow Rate feed is trusted and users of rate hook adopt oracle risk of buying/selling credit at unsatisfactory prices
The insurance fund (out of scope for this project) may not be able to make all lenders whole, maybe unfair, and may be manipulated
LiquidateWithReplacement might not be available for the big enough debt positions
All issues acknowledged on previous audits and automated findings

Deployment

Environment Setup

Ensure your .env file in the root directory of your project contains the following variables:

API_KEY_ALCHEMY=<Your Alchemy API Key>
API_KEY_ETHERSCAN=<Your Etherscan API Key>
DEPLOYER_ADDRESS=<Deployer's Ethereum Address>
DEPLOYER_ACCOUNT=<Name of the Deployer's Account in Foundry>
OWNER=<Owner's Address>
FEE_RECIPIENT=<Fee Recipient's Address>
NETWORK_CONFIGURATION=<Network Configuration>
RPC_URL=<Network Name>

Account Management

The DEPLOYER_ACCOUNT is a reference to the name of an account managed by Foundry's cast wallet feature. To create and import a new deployer wallet using a private key, use the following command:

cast wallet import DEPLOYER_ACCOUNT_NAME --private-key $(cast wallet new | grep Private | awk -F 'Private key: ' '{print $2}')

Network Configuration

Ensure that the NETWORK_CONFIGURATION is set according to the network options you are deploying to. For example, you can create a configuration base-mocks and another base-production without mocks. Also, ensure that RPC_URL is set according to the network you are deploying to. In the previous case, both would be equal to base as in your foundry.toml. You can see the available network configuration in script/Networks.sol.

You can set relevant NetworkParams to address(0) if you are deploying with mock contracts or require specific network parameters.

source .env
export NETWORK_CONFIGURATION=base-production-weth-usdc
forge script script/Deploy.s.sol --rpc-url $RPC_URL --gas-limit 30000000 --sender $DEPLOYER_ADDRESS --account $DEPLOYER_ACCOUNT --ffi --verify -vvvvv

If it does not work, try removing --verify

Deployment checklist

Due dilligence on borrow/collateral tokens: non-rebasing, IERC20Metadata
Deploy
Grant KEEPER_ROLE to liquidation contract
Grant BORROW_RATE_UPDATER_ROLE to bot
Grant PAUSER_ROLE to bot, multisig signers

Upgrade

source .env.base_sepolia
forge script script/Upgrade.s.sol --rpc-url $RPC_URL --gas-limit 30000000 --sender $DEPLOYER_ADDRESS --account $DEPLOYER_ACCOUNT --ffi --verify -vvvvv [--slow]

Name		Name	Last commit message	Last commit date
Latest commit History 676 Commits
.github/workflows		.github/workflows
audits		audits
broadcast		broadcast
deployments		deployments
deprecated		deprecated
lib		lib
script		script
src		src
test		test
.gas-snapshot		.gas-snapshot
.gitignore		.gitignore
.gitmodules		.gitmodules
.solhint.json		.solhint.json
LICENSE		LICENSE
README.md		README.md
echidna.yaml		echidna.yaml
foundry.toml		foundry.toml
medusa-differential.json		medusa-differential.json
medusa.json		medusa.json
package-lock.json		package-lock.json
package.json		package.json
remappings.txt		remappings.txt
size.png		size.png
slither.config.json		slither.config.json

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size-solidity

Audits

Documentation

Overview, Accounting and Protocol Design

Technical overview

Architecture

Tokens

Maths

Oracles

Price Feed

Variable Pool Borrow Rate Feed

Copy trading

Test

Coverage

FIles

Tests per file

Protocol invariants

Invariants implemented

Onchain fuzzing

Formal Verification

Known limitations

Deployment

Environment Setup

Account Management

Network Configuration

Deployment checklist

Upgrade

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size-solidity

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Documentation

Overview, Accounting and Protocol Design

Technical overview

Architecture

Tokens

Maths

Oracles

Price Feed

Variable Pool Borrow Rate Feed

Copy trading

Test

Coverage

FIles

Tests per file

Protocol invariants

Invariants implemented

Onchain fuzzing

Formal Verification

Known limitations

Deployment

Environment Setup

Account Management

Network Configuration

Deployment checklist

Upgrade

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