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PhEVM (Phylax EVM) is a specialized EVM implementation that executes assertion bytecode during transaction validation. It extends the standard EVM with additional capabilities for state inspection and comparison.

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Purpose

PhEVM serves as the execution engine within the Assertion Enforcer. When a transaction needs validation, the Assertion Enforcer invokes PhEVM to run all relevant assertions against the transaction’s state changes. See the system architecture diagram for how PhEVM fits into the overall Credible Layer architecture.

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Key Capabilities

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State Access

PhEVM can access blockchain state at multiple points during transaction execution:
  • Pre-transaction state: The blockchain state before the transaction executes
  • Post-transaction state: The blockchain state after the transaction executes
  • Pre-call state: State before a specific internal call within the transaction
  • Post-call state: State after a specific internal call within the transaction
This enables assertions to compare values across different execution points, something impossible with standard Solidity.

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Cheatcodes

PhEVM implements special precompiles called cheatcodes that provide capabilities beyond standard EVM operations:
  • State forking: forkPreTx(), forkPostTx(), forkPreCall(), forkPostCall()
  • Call introspection: Access to call inputs, call traces, and execution context
  • State change tracking: Monitor storage slot modifications during execution
  • Log access: Retrieve transaction logs for validation
These cheatcodes are exposed through the credible-std library and documented in the Cheatcodes Reference.

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Off-Chain Execution

PhEVM runs entirely off-chain as part of the Assertion Enforcer sidecar. This provides several advantages:
  • Higher gas limits: Assertions can perform complex computations that would be prohibitively expensive on-chain
  • No on-chain overhead: Validation doesn’t consume block gas or affect transaction costs
  • Parallel execution: Multiple assertions can be validated simultaneously

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How It Works

When the Assertion Enforcer receives a transaction for validation:
  1. State Preparation: PhEVM receives the pre-transaction and post-transaction state snapshots
  2. Assertion Loading: Relevant assertion bytecode is loaded from cache (fetched from Assertion DA during deployment)
  3. Execution: PhEVM executes each assertion function against the prepared states
  4. Result: If any assertion reverts, the transaction is flagged as invalid
For the complete validation flow, see Assertion Enforcer.