Yield Delegation / Rebasing Token Rewrite

.gitignore

@@ -84,3 +84,6 @@ fork-coverage
 unit-coverage
 
 .VSCodeCounter
+
+# Certora #
+.certora_internal

certora/confs/OUSD_accounting.conf

@@ -0,0 +1,16 @@
+{
+    "files": [
+        "contracts/contracts/token/OUSD.sol"
+    ],
+    "msg": "OUSD Accounting invariants",
+    "packages": [
+        "@openzeppelin/contracts=contracts/lib/openzeppelin/contracts",
+    ],
+    "process": "emv",
+    "prover_args": [
+
+    ],
+    "solc": "solc8.28",
+    "verify": "OUSD:certora/specs/OUSD/AccountInvariants.spec",
+    "server": "production",
+}

certora/confs/OUSD_balances.conf

@@ -0,0 +1,18 @@
+{
+    "files": [
+        "contracts/contracts/token/OUSD.sol"
+    ],
+    "msg": "OUSD Balances invariants",
+    "packages": [
+        "@openzeppelin/contracts=contracts/lib/openzeppelin/contracts",
+    ],
+    "process": "emv",
+    "prover_args": [
+        "-mediumTimeout 40",
+    ],
+    "multi_assert_check":true,
+    "smt_timeout":"1000",
+    "solc": "solc8.28",
+    "verify": "OUSD:certora/specs/OUSD/BalanceInvariants.spec",
+    "server": "production"
+}

certora/confs/OUSD_other.conf

@@ -0,0 +1,17 @@
+{
+    "files": [
+        "contracts/contracts/token/OUSD.sol"
+    ],
+    "msg": "OUSD other invariants",
+    "packages": [
+        "@openzeppelin/contracts=contracts/lib/openzeppelin/contracts",
+    ],
+    "process": "emv",
+    "prover_args": [
+        "-mediumTimeout 40",
+    ],
+    "smt_timeout":"1000",
+    "solc": "solc8.28",
+    "verify": "OUSD:certora/specs/OUSD/OtherInvariants.spec",
+    "server": "production"
+}

certora/confs/OUSD_sumOfBalances.conf

@@ -0,0 +1,19 @@
+{
+    "files": [
+        "contracts/contracts/token/OUSD.sol"
+    ],
+    "msg": "OUSD Sum of balances rules",
+    "packages": [
+        "@openzeppelin/contracts=contracts/lib/openzeppelin/contracts",
+    ],
+    "process": "emv",
+    "prover_args": [
+        "-mediumTimeout 40",
+        "-s [z3:lia2,z3:arith1,yices:def]",
+    ],
+    "multi_assert_check":true,
+    "smt_timeout":"1000",
+    "solc": "solc8.28",
+    "verify": "OUSD:certora/specs/OUSD/SumOfBalances.spec",
+    "server": "production"
+}

certora/run.sh

@@ -0,0 +1,4 @@
+certoraRun certora/confs/OUSD_accounting.conf
+certoraRun certora/confs/OUSD_balances.conf
+certoraRun certora/confs/OUSD_other.conf
+certoraRun certora/confs/OUSD_sumOfBalances.conf

certora/specs/OUSD/AccountInvariants.spec

@@ -0,0 +1,158 @@
+import "./common.spec";
+
+function allAccountValidState() {
+    requireInvariant DelegationAccountsCorrelation();
+    requireInvariant DelegationValidRebaseState();
+    requireInvariant stdNonRebasingDoesntYield();
+    requireInvariant alternativeCreditsPerTokenIsOneOrZeroOnly();
+    requireInvariant yieldDelegationSourceHasNonZeroYeildTo();
+    requireInvariant yieldDelegationTargetHasNonZeroYeildFrom();
+    requireInvariant yieldToOfZeroIsZero();
+    requireInvariant yieldFromOfZeroIsZero();
+    requireInvariant cantYieldToSelf();
+    requireInvariant cantYieldFromSelf();
+    requireInvariant zeroAlternativeCreditsPerTokenStates();
+    requireInvariant nonZeroAlternativeCreditsPerTokenStates();
+}
+
+/// @title Any non zero valued YieldTo points to an account that has a YieldFrom pointing back to the starting account and vice versa.
+/// @property Account Invariants
+invariant DelegationAccountsCorrelation()
+    forall address account.
+        (OUSD.yieldTo[account] != 0 => (OUSD.yieldFrom[OUSD.yieldTo[account]] == account)) 
+        &&
+        (OUSD.yieldFrom[account] != 0 => (OUSD.yieldTo[OUSD.yieldFrom[account]] == account))
+    {
+        preserved with (env e) {
+            requireInvariant DelegationValidRebaseState();
+            requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+        }
+    }
+
+/// @title Any non zero valued YieldTo points to an account Iff that account is in YieldDelegationSource state and 
+/// Any non zero valued YieldFrom points to an account Iff that account is in YieldDelegationTarget state.
+/// @property Account Invariants
+invariant DelegationValidRebaseState()
+    forall address account. 
+        (OUSD.yieldTo[account] != 0 <=> OUSD.rebaseState[account] == YieldDelegationSource())
+        &&
+        (OUSD.yieldFrom[account] != 0 <=> OUSD.rebaseState[account] == YieldDelegationTarget())
+    {
+        preserved with (env e) {
+            requireInvariant DelegationAccountsCorrelation();
+            requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+        }
+    }
+
+/// @title Any account with a zero value in alternativeCreditsPerToken has a rebaseState that is one of (NotSet, StdRebasing, or YieldDelegationTarget)
+/// @property Account Invariants
+invariant zeroAlternativeCreditsPerTokenStates()
+    forall address account . OUSD.alternativeCreditsPerToken[account] == 0 <=> (OUSD.rebaseState[account] == NotSet() || 
+                                                OUSD.rebaseState[account] == StdRebasing() || 
+                                                OUSD.rebaseState[account] == YieldDelegationTarget())
+    {
+        preserved {
+            requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+            requireInvariant DelegationAccountsCorrelation();
+            requireInvariant DelegationValidRebaseState();
+        }
+    }
+
+/// @title Any account with value of 1e18 in alternativeCreditsPerToken has a rebaseState that is one of (StdNonRebasing, YieldDelegationSource)
+/// @property Account Invariants
+invariant nonZeroAlternativeCreditsPerTokenStates()
+    forall address account . OUSD.alternativeCreditsPerToken[account] != 0 <=> (OUSD.rebaseState[account] == StdNonRebasing() ||  
+                                                OUSD.rebaseState[account] == YieldDelegationSource())
+    {
+        preserved undelegateYield(address _account) with (env e) {
+            requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+            requireInvariant DelegationAccountsCorrelation();
+            requireInvariant DelegationValidRebaseState();
+        }
+    }
+
+/// @title The result of balanceOf of any account in StdNonRebasing state equals the account's credit-balance.
+/// @property Balance Invariants
+invariant stdNonRebasingBalanceEqCreditBalances(address account)
+	OUSD.rebaseState[account] == StdNonRebasing() => OUSD.balanceOf(account) == OUSD.creditBalances[account]
+	{
+		preserved {
+			requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+            requireInvariant DelegationAccountsCorrelation();
+            requireInvariant DelegationValidRebaseState();
+            requireInvariant nonZeroAlternativeCreditsPerTokenStates();
+            requireInvariant stdNonRebasingDoesntYield();
+            requireInvariant alternativeCreditsPerTokenIsOneOrZeroOnly();
+		}
+	}
+
+/// @title Any account in StdNonRebasing state doesn't yield to no account.
+/// @property Account Invariants
+invariant stdNonRebasingDoesntYield()
+    forall address account . OUSD.rebaseState[account] == StdNonRebasing() => OUSD.yieldTo[account] == 0
+    {
+		preserved {
+			requireInvariant yieldToOfZeroIsZero();
+            requireInvariant yieldFromOfZeroIsZero();
+            requireInvariant DelegationAccountsCorrelation();
+            requireInvariant DelegationValidRebaseState();
+		}
+	}
+
+/// @title alternativeCreditsPerToken can only be set to 0 or 1e18, no other values
+/// @property Account Invariants
+invariant alternativeCreditsPerTokenIsOneOrZeroOnly()
+    forall address account . OUSD.alternativeCreditsPerToken[account] == 0 || OUSD.alternativeCreditsPerToken[account] == e18();
+
+/// @title Any account with rebaseState = YieldDelegationSource has a nonZero yieldTo
+/// @property Account Invariants
+invariant yieldDelegationSourceHasNonZeroYeildTo()
+    forall address account . OUSD.rebaseState[account] == YieldDelegationSource() => OUSD.yieldTo[account] != 0;
+
+/// @title Any account with rebaseState = YieldDelegationTarget has a nonZero yieldFrom
+/// @property Account Invariants
+invariant yieldDelegationTargetHasNonZeroYeildFrom()
+    forall address account . OUSD.rebaseState[account] == YieldDelegationTarget() => OUSD.yieldFrom[account] != 0;
+
+// Helper Invariants
+/// @title yieldTo of zero is zero
+/// @property Account Invariants
+invariant yieldToOfZeroIsZero()
+    yieldTo(0) == 0;
+
+/// @title yieldFrom of zero is zero
+/// @property Account Invariants
+invariant yieldFromOfZeroIsZero()
+    yieldFrom(0) == 0;
+
+/// @title yieldTo of an account can't be the same as the account
+/// @property Account Invariants
+invariant cantYieldToSelf()
+    forall address account . OUSD.yieldTo[account] != 0 => OUSD.yieldTo[account] != account;
+
+/// @title yieldFrom of an account can't be the same as the account
+/// @property Account Invariants
+invariant cantYieldFromSelf()
+    forall address account . OUSD.yieldFrom[account] != 0 => OUSD.yieldFrom[account] != account;
+
+/// @title Only delegation changes the different effective identity.
+/// @property Account Invariants
+rule onlyDelegationChangesPairingState(address accountA, address accountB, method f) 
+filtered{f -> !f.isView}
+{
+    bool different_before = differentAccounts(accountA, accountB);
+    env e;
+    calldataarg args;
+    f(e, args);
+    bool different_after = differentAccounts(accountA, accountB);
+
+    if(delegateMethods(f)) {
+        satisfy different_before != different_after;
+    }
+    assert different_before != different_after => delegateMethods(f);
+}