Explain the difference between `require()`, `assert()`, and `revert()` in Solidity and their security implications.

These are Solidity's error handling mechanisms with different use cases:

require(condition, "message"):

• Used for input validation and external conditions
• Refunds remaining gas when condition fails
• Should be used for user input validation and external contract calls

assert(condition):

• Used for internal consistency checks and invariants
• Consumes all remaining gas when condition fails
• Should only fail if there's a bug in the contract

revert("message"):

• Unconditionally reverts with a custom message
• Refunds remaining gas
• Used for complex conditional logic

function withdraw(uint amount) external {
    require(amount > 0, "Amount must be positive"); // Input validation
    require(balances[msg.sender] >= amount, "Insufficient balance"); // State validation
    
    balances[msg.sender] -= amount;
    assert(balances[msg.sender] >= 0); // Internal invariant check
    
    if (!payable(msg.sender).send(amount)) {
        revert("Transfer failed"); // Complex condition handling
    }
}

Security Implication: Misusing assert() for input validation can lead to unnecessary gas consumption attacks.