Receipt reuse and forgery tools

README.md

@@ -1,42 +1,42 @@
-# pwn_w3bridges
+# pwn w3bridges
+Workshop for "web3" bridge hacking at Hacktivity 2022
 
-Workshop for web3 bridge hacking at Hacktivity 2022
+## Agenda
 
+#### Introduction
+- Web3 vs web2 hacking, concepts / workshop topology
 
-# Scenario 1 - Receipt reuse - Topology
+#### Environment setup, system requirements
+- Any browser for Ethereum, Remix
+- Substrate, Rust nightly
 
-Story: Substrate system being built after ERC20 token is sold.
+#### Scenario 1: Token on two chains, mint using receipt
+- Solidity basics, using remix for compile
+- Exploit visibility, take admin
+- ECDSA Ethereum basics
+- Mint with receipt -> Find the vuln!
 
-- Substrate node with EVM pallet || Token minter smart contract (vuln here)
-- Bridge providing receipts || Checks bridge balance on Substrate node
-- Ethereum node || Token minter smart contract (target for mint)
+#### Scenario 2: Signature forgery (any chain)
+- Deploy SC on Ethereum chain
+- Compile Substrate with EVM
+- Deploy SC
+- Test ECDSA signature forgery exploit from one to other
 
+## Resources
+
+#### Scenario 1
 https://remix.ethereum.org/
-Faucet?
+https://www.tutorialspoint.com/solidity/solidity_operators.htm
 https://polkadot.js.org/apps/
 https://ethereum.org/en/developers/docs/standards/tokens/erc-20/
 https://git.hsbp.org/six/eth_keygen
 
+#### Scenario 2
 https://github.com/paritytech/substrate-contracts-node
 https://docs.substrate.io/quick-start/
-https://substrate.io/developers/playground/ | alternative
 https://github.com/substrate-developer-hub/substrate-front-end-template
-
-
-## Commands
-$
-
-# Scenario 2 - ECDSA signature forgery - Topology
-
-Story: ink! smart contract interoperability.
-
-- Substrate node with ink!
-- No bridge, but signature forgery
-- Ethereum node
-
 https://github.com/paritytech/ink
+https://github.com/paritytech/substrate/blob/master/primitives/core/src/ecdsa.rs
 https://use.ink/getting-started/setup
 https://medium.com/block-journal/introducing-substrate-smart-contracts-with-ink-d486289e2b59
-
-## Commands
-$
+https://substrate.io/developers/playground/

ink/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "erc20"
+version = "4.0.0-alpha.3"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2021"
+publish = false
+
+[dependencies]
+ink = { path = "../../crates/ink", default-features = false }
+
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
+scale-info = { version = "2", default-features = false, features = ["derive"], optional = true }
+
+[lib]
+name = "erc20"
+path = "lib.rs"
+crate-type = ["cdylib"]
+
+[features]
+default = ["std"]
+std = [
+    "ink/std",
+    "scale/std",
+    "scale-info/std",
+]
+ink-as-dependency = []

ink/lib.rs

@@ -0,0 +1,532 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[ink::contract]
+mod erc20 {
+    use ink::storage::Mapping;
+
+    /// A simple ERC-20 contract.
+    #[ink(storage)]
+    #[derive(Default)]
+    pub struct Erc20 {
+        /// Total token supply.
+        total_supply: Balance,
+        /// Mapping from owner to number of owned token.
+        balances: Mapping<AccountId, Balance>,
+        /// Mapping of the token amount which an account is allowed to withdraw
+        /// from another account.
+        allowances: Mapping<(AccountId, AccountId), Balance>,
+    }
+
+    /// Event emitted when a token transfer occurs.
+    #[ink(event)]
+    pub struct Transfer {
+        #[ink(topic)]
+        from: Option<AccountId>,
+        #[ink(topic)]
+        to: Option<AccountId>,
+        value: Balance,
+    }
+
+    /// Event emitted when an approval occurs that `spender` is allowed to withdraw
+    /// up to the amount of `value` tokens from `owner`.
+    #[ink(event)]
+    pub struct Approval {
+        #[ink(topic)]
+        owner: AccountId,
+        #[ink(topic)]
+        spender: AccountId,
+        value: Balance,
+    }
+
+    /// The ERC-20 error types.
+    #[derive(Debug, PartialEq, Eq, scale::Encode, scale::Decode)]
+    #[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
+    pub enum Error {
+        /// Returned if not enough balance to fulfill a request is available.
+        InsufficientBalance,
+        /// Returned if not enough allowance to fulfill a request is available.
+        InsufficientAllowance,
+    }
+
+    /// The ERC-20 result type.
+    pub type Result<T> = core::result::Result<T, Error>;
+
+    impl Erc20 {
+        /// Creates a new ERC-20 contract with the specified initial supply.
+        #[ink(constructor)]
+        pub fn new(total_supply: Balance) -> Self {
+            let mut balances = Mapping::default();
+            let caller = Self::env().caller();
+            balances.insert(&caller, &total_supply);
+            Self::env().emit_event(Transfer {
+                from: None,
+                to: Some(caller),
+                value: total_supply,
+            });
+            Self {
+                total_supply,
+                balances,
+                allowances: Default::default(),
+            }
+        }
+
+        /// Returns the total token supply.
+        #[ink(message)]
+        pub fn total_supply(&self) -> Balance {
+            self.total_supply
+        }
+
+        /// Returns the account balance for the specified `owner`.
+        ///
+        /// Returns `0` if the account is non-existent.
+        #[ink(message)]
+        pub fn balance_of(&self, owner: AccountId) -> Balance {
+            self.balance_of_impl(&owner)
+        }
+
+        /// Returns the account balance for the specified `owner`.
+        ///
+        /// Returns `0` if the account is non-existent.
+        ///
+        /// # Note
+        ///
+        /// Prefer to call this method over `balance_of` since this
+        /// works using references which are more efficient in Wasm.
+        #[inline]
+        fn balance_of_impl(&self, owner: &AccountId) -> Balance {
+            self.balances.get(owner).unwrap_or_default()
+        }
+
+        /// Returns the amount which `spender` is still allowed to withdraw from `owner`.
+        ///
+        /// Returns `0` if no allowance has been set.
+        #[ink(message)]
+        pub fn allowance(&self, owner: AccountId, spender: AccountId) -> Balance {
+            self.allowance_impl(&owner, &spender)
+        }
+
+        /// Returns the amount which `spender` is still allowed to withdraw from `owner`.
+        ///
+        /// Returns `0` if no allowance has been set.
+        ///
+        /// # Note
+        ///
+        /// Prefer to call this method over `allowance` since this
+        /// works using references which are more efficient in Wasm.
+        #[inline]
+        fn allowance_impl(&self, owner: &AccountId, spender: &AccountId) -> Balance {
+            self.allowances.get((owner, spender)).unwrap_or_default()
+        }
+
+        /// Transfers `value` amount of tokens from the caller's account to account `to`.
+        ///
+        /// On success a `Transfer` event is emitted.
+        ///
+        /// # Errors
+        ///
+        /// Returns `InsufficientBalance` error if there are not enough tokens on
+        /// the caller's account balance.
+        #[ink(message)]
+        pub fn transfer(&mut self, to: AccountId, value: Balance) -> Result<()> {
+            let from = self.env().caller();
+            self.transfer_from_to(&from, &to, value)
+        }
+
+        /// Allows `spender` to withdraw from the caller's account multiple times, up to
+        /// the `value` amount.
+        ///
+        /// If this function is called again it overwrites the current allowance with `value`.
+        ///
+        /// An `Approval` event is emitted.
+        #[ink(message)]
+        pub fn approve(&mut self, spender: AccountId, value: Balance) -> Result<()> {
+            let owner = self.env().caller();
+            self.allowances.insert((&owner, &spender), &value);
+            self.env().emit_event(Approval {
+                owner,
+                spender,
+                value,
+            });
+            Ok(())
+        }
+
+        /// Transfers `value` tokens on the behalf of `from` to the account `to`.
+        ///
+        /// This can be used to allow a contract to transfer tokens on ones behalf and/or
+        /// to charge fees in sub-currencies, for example.
+        ///
+        /// On success a `Transfer` event is emitted.
+        ///
+        /// # Errors
+        ///
+        /// Returns `InsufficientAllowance` error if there are not enough tokens allowed
+        /// for the caller to withdraw from `from`.
+        ///
+        /// Returns `InsufficientBalance` error if there are not enough tokens on
+        /// the account balance of `from`.
+        #[ink(message)]
+        pub fn transfer_from(
+            &mut self,
+            from: AccountId,
+            to: AccountId,
+            value: Balance,
+        ) -> Result<()> {
+            let caller = self.env().caller();
+            let allowance = self.allowance_impl(&from, &caller);
+            if allowance < value {
+                return Err(Error::InsufficientAllowance)
+            }
+            self.transfer_from_to(&from, &to, value)?;
+            self.allowances
+                .insert((&from, &caller), &(allowance - value));
+            Ok(())
+        }
+
+        /// Transfers `value` amount of tokens from the caller's account to account `to`.
+        ///
+        /// On success a `Transfer` event is emitted.
+        ///
+        /// # Errors
+        ///
+        /// Returns `InsufficientBalance` error if there are not enough tokens on
+        /// the caller's account balance.
+        fn transfer_from_to(
+            &mut self,
+            from: &AccountId,
+            to: &AccountId,
+            value: Balance,
+        ) -> Result<()> {
+            let from_balance = self.balance_of_impl(from);
+            if from_balance < value {
+                return Err(Error::InsufficientBalance)
+            }
+
+            self.balances.insert(from, &(from_balance - value));
+            let to_balance = self.balance_of_impl(to);
+            self.balances.insert(to, &(to_balance + value));
+            self.env().emit_event(Transfer {
+                from: Some(*from),
+                to: Some(*to),
+                value,
+            });
+            Ok(())
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+
+        use ink::primitives::Clear;
+
+        type Event = <Erc20 as ::ink::reflect::ContractEventBase>::Type;
+
+        fn assert_transfer_event(
+            event: &ink::env::test::EmittedEvent,
+            expected_from: Option<AccountId>,
+            expected_to: Option<AccountId>,
+            expected_value: Balance,
+        ) {
+            let decoded_event = <Event as scale::Decode>::decode(&mut &event.data[..])
+                .expect("encountered invalid contract event data buffer");
+            if let Event::Transfer(Transfer { from, to, value }) = decoded_event {
+                assert_eq!(from, expected_from, "encountered invalid Transfer.from");
+                assert_eq!(to, expected_to, "encountered invalid Transfer.to");
+                assert_eq!(value, expected_value, "encountered invalid Trasfer.value");
+            } else {
+                panic!("encountered unexpected event kind: expected a Transfer event")
+            }
+            let expected_topics = vec![
+                encoded_into_hash(&PrefixedValue {
+                    value: b"Erc20::Transfer",
+                    prefix: b"",
+                }),
+                encoded_into_hash(&PrefixedValue {
+                    prefix: b"Erc20::Transfer::from",
+                    value: &expected_from,
+                }),
+                encoded_into_hash(&PrefixedValue {
+                    prefix: b"Erc20::Transfer::to",
+                    value: &expected_to,
+                }),
+                encoded_into_hash(&PrefixedValue {
+                    prefix: b"Erc20::Transfer::value",
+                    value: &expected_value,
+                }),
+            ];
+
+            let topics = event.topics.clone();
+            for (n, (actual_topic, expected_topic)) in
+                topics.iter().zip(expected_topics).enumerate()
+            {
+                let mut topic_hash = Hash::clear();
+                let len = actual_topic.len();
+                topic_hash.as_mut()[0..len].copy_from_slice(&actual_topic[0..len]);
+
+                assert_eq!(
+                    topic_hash, expected_topic,
+                    "encountered invalid topic at {}",
+                    n
+                );
+            }
+        }
+
+        /// The default constructor does its job.
+        #[ink::test]
+        fn new_works() {
+            // Constructor works.
+            let _erc20 = Erc20::new(100);
+
+            // Transfer event triggered during initial construction.
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_eq!(1, emitted_events.len());
+
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+        }
+
+        /// The total supply was applied.
+        #[ink::test]
+        fn total_supply_works() {
+            // Constructor works.
+            let erc20 = Erc20::new(100);
+            // Transfer event triggered during initial construction.
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+            // Get the token total supply.
+            assert_eq!(erc20.total_supply(), 100);
+        }
+
+        /// Get the actual balance of an account.
+        #[ink::test]
+        fn balance_of_works() {
+            // Constructor works
+            let erc20 = Erc20::new(100);
+            // Transfer event triggered during initial construction
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+            // Alice owns all the tokens on contract instantiation
+            assert_eq!(erc20.balance_of(accounts.alice), 100);
+            // Bob does not owns tokens
+            assert_eq!(erc20.balance_of(accounts.bob), 0);
+        }
+
+        #[ink::test]
+        fn transfer_works() {
+            // Constructor works.
+            let mut erc20 = Erc20::new(100);
+            // Transfer event triggered during initial construction.
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+
+            assert_eq!(erc20.balance_of(accounts.bob), 0);
+            // Alice transfers 10 tokens to Bob.
+            assert_eq!(erc20.transfer(accounts.bob, 10), Ok(()));
+            // Bob owns 10 tokens.
+            assert_eq!(erc20.balance_of(accounts.bob), 10);
+
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_eq!(emitted_events.len(), 2);
+            // Check first transfer event related to ERC-20 instantiation.
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+            // Check the second transfer event relating to the actual trasfer.
+            assert_transfer_event(
+                &emitted_events[1],
+                Some(AccountId::from([0x01; 32])),
+                Some(AccountId::from([0x02; 32])),
+                10,
+            );
+        }
+
+        #[ink::test]
+        fn invalid_transfer_should_fail() {
+            // Constructor works.
+            let mut erc20 = Erc20::new(100);
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+
+            assert_eq!(erc20.balance_of(accounts.bob), 0);
+
+            // Set the contract as callee and Bob as caller.
+            let contract = ink::env::account_id::<ink::env::DefaultEnvironment>();
+            ink::env::test::set_callee::<ink::env::DefaultEnvironment>(contract);
+            ink::env::test::set_caller::<ink::env::DefaultEnvironment>(accounts.bob);
+
+            // Bob fails to transfers 10 tokens to Eve.
+            assert_eq!(
+                erc20.transfer(accounts.eve, 10),
+                Err(Error::InsufficientBalance)
+            );
+            // Alice owns all the tokens.
+            assert_eq!(erc20.balance_of(accounts.alice), 100);
+            assert_eq!(erc20.balance_of(accounts.bob), 0);
+            assert_eq!(erc20.balance_of(accounts.eve), 0);
+
+            // Transfer event triggered during initial construction.
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_eq!(emitted_events.len(), 1);
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+        }
+
+        #[ink::test]
+        fn transfer_from_works() {
+            // Constructor works.
+            let mut erc20 = Erc20::new(100);
+            // Transfer event triggered during initial construction.
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+
+            // Bob fails to transfer tokens owned by Alice.
+            assert_eq!(
+                erc20.transfer_from(accounts.alice, accounts.eve, 10),
+                Err(Error::InsufficientAllowance)
+            );
+            // Alice approves Bob for token transfers on her behalf.
+            assert_eq!(erc20.approve(accounts.bob, 10), Ok(()));
+
+            // The approve event takes place.
+            assert_eq!(ink::env::test::recorded_events().count(), 2);
+
+            // Set the contract as callee and Bob as caller.
+            let contract = ink::env::account_id::<ink::env::DefaultEnvironment>();
+            ink::env::test::set_callee::<ink::env::DefaultEnvironment>(contract);
+            ink::env::test::set_caller::<ink::env::DefaultEnvironment>(accounts.bob);
+
+            // Bob transfers tokens from Alice to Eve.
+            assert_eq!(
+                erc20.transfer_from(accounts.alice, accounts.eve, 10),
+                Ok(())
+            );
+            // Eve owns tokens.
+            assert_eq!(erc20.balance_of(accounts.eve), 10);
+
+            // Check all transfer events that happened during the previous calls:
+            let emitted_events = ink::env::test::recorded_events().collect::<Vec<_>>();
+            assert_eq!(emitted_events.len(), 3);
+            assert_transfer_event(
+                &emitted_events[0],
+                None,
+                Some(AccountId::from([0x01; 32])),
+                100,
+            );
+            // The second event `emitted_events[1]` is an Approve event that we skip checking.
+            assert_transfer_event(
+                &emitted_events[2],
+                Some(AccountId::from([0x01; 32])),
+                Some(AccountId::from([0x05; 32])),
+                10,
+            );
+        }
+
+        #[ink::test]
+        fn allowance_must_not_change_on_failed_transfer() {
+            let mut erc20 = Erc20::new(100);
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+
+            // Alice approves Bob for token transfers on her behalf.
+            let alice_balance = erc20.balance_of(accounts.alice);
+            let initial_allowance = alice_balance + 2;
+            assert_eq!(erc20.approve(accounts.bob, initial_allowance), Ok(()));
+
+            // Get contract address.
+            let callee = ink::env::account_id::<ink::env::DefaultEnvironment>();
+            ink::env::test::set_callee::<ink::env::DefaultEnvironment>(callee);
+            ink::env::test::set_caller::<ink::env::DefaultEnvironment>(accounts.bob);
+
+            // Bob tries to transfer tokens from Alice to Eve.
+            let emitted_events_before = ink::env::test::recorded_events().count();
+            assert_eq!(
+                erc20.transfer_from(accounts.alice, accounts.eve, alice_balance + 1),
+                Err(Error::InsufficientBalance)
+            );
+            // Allowance must have stayed the same
+            assert_eq!(
+                erc20.allowance(accounts.alice, accounts.bob),
+                initial_allowance
+            );
+            // No more events must have been emitted
+            assert_eq!(
+                emitted_events_before,
+                ink::env::test::recorded_events().count()
+            )
+        }
+
+        /// For calculating the event topic hash.
+        struct PrefixedValue<'a, 'b, T> {
+            pub prefix: &'a [u8],
+            pub value: &'b T,
+        }
+
+        impl<X> scale::Encode for PrefixedValue<'_, '_, X>
+        where
+            X: scale::Encode,
+        {
+            #[inline]
+            fn size_hint(&self) -> usize {
+                self.prefix.size_hint() + self.value.size_hint()
+            }
+
+            #[inline]
+            fn encode_to<T: scale::Output + ?Sized>(&self, dest: &mut T) {
+                self.prefix.encode_to(dest);
+                self.value.encode_to(dest);
+            }
+        }
+
+        fn encoded_into_hash<T>(entity: &T) -> Hash
+        where
+            T: scale::Encode,
+        {
+            use ink::{
+                env::hash::{
+                    Blake2x256,
+                    CryptoHash,
+                    HashOutput,
+                },
+                primitives::Clear,
+            };
+
+            let mut result = Hash::clear();
+            let len_result = result.as_ref().len();
+            let encoded = entity.encode();
+            let len_encoded = encoded.len();
+            if len_encoded <= len_result {
+                result.as_mut()[..len_encoded].copy_from_slice(&encoded);
+                return result
+            }
+            let mut hash_output =
+                <<Blake2x256 as HashOutput>::Type as Default>::default();
+            <Blake2x256 as CryptoHash>::hash(&encoded, &mut hash_output);
+            let copy_len = core::cmp::min(hash_output.len(), len_result);
+            result.as_mut()[0..copy_len].copy_from_slice(&hash_output[0..copy_len]);
+            result
+        }
+    }
+}

python/forgery.py

@@ -0,0 +1,50 @@
+#!/usr/bin/python3
+# Author: SI
+
+from eth_account.account import to_standard_signature_bytes
+from eth_keys import keys
+from eth_utils import (big_endian_to_int, to_bytes)
+from hexbytes import HexBytes
+from eth_keys.backends.native.jacobian import (inv, fast_multiply, fast_add)
+from eth_keys.constants import (SECPK1_G as G, SECPK1_N as N)
+
+def recover_public_key(message_hash, signature):
+	message_hash_bytes = HexBytes(message_hash)
+	if len(message_hash_bytes) != 32:
+		raise ValueError("The message hash must be exactly 32-bytes")
+	signature_bytes = HexBytes(signature)
+	signature_obj = keys.Signature(signature_bytes = to_standard_signature_bytes(signature_bytes))
+	return signature_obj.recover_public_key_from_msg_hash(message_hash_bytes)
+
+def forge(public_key, a = 0, b = 1):
+	t = public_key.to_bytes()
+	Y = big_endian_to_int(t[:32]), big_endian_to_int(t[32:])
+
+	r, y = fast_add(fast_multiply(G, a), fast_multiply(Y, b))
+
+	s_raw = r * inv(b, N) % N
+	v_raw = (y % 2) ^ (0 if s_raw * 2 < N else 1)
+	s = s_raw if s_raw * 2 < N else N - s_raw
+	v = v_raw + 27
+
+	z = a * s_raw % N
+
+	eth_signature_bytes = to_bytes(r).rjust(32, b'\0') + to_bytes(s).rjust(32, b'\0') + to_bytes(v)
+
+	return '0x' + to_bytes(z).rjust(32, b'\0').hex(), '0x' + eth_signature_bytes.hex()
+
+hsh = '0xe50051a0af89748fe098cef3b163b6dc586a664e726791bb2a582ad364f42683'
+sig = '0x2bdbc1826efc039719a28a9f4dbab9f4a2692d83de478300261a0e49019b63ee67c202ecc4ebdf82693da47824ac4fcf21f793400d85696034c4de9537c6ce491b'
+
+pub = recover_public_key(hsh, sig)
+addr = pub.to_checksum_address()
+print('recovered (checksum) address:', addr)
+
+a, b = 0, 1
+fhsh, fsig = forge(pub, a, b)
+print('forged message hash:', fhsh)
+print('forged signature:', fsig)
+
+fpub = recover_public_key(fhsh, fsig)
+faddr = fpub.to_checksum_address()
+print('recovered address check:', 'correct' if faddr == addr else 'wrong!')

solidity/cctf9v1.sol

@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: Apache-2.0
+// Authors: six and Silur
+pragma solidity ^0.8.16;
+
+contract CCTF9 {
+  address public admin;
+  uint256 public volStart;
+  uint256 public volMaxPoints;
+  uint256 public powDiff;
+  bool public started;
+
+  enum PlayerStatus {
+    Unverified,
+    Verified,
+    Banned
+  }
+
+  struct Player {
+    PlayerStatus status;
+    uint256 points;
+  }
+
+  modifier onlyAdmin {
+    require(msg.sender == admin, "Not admin");
+    _;
+  }
+
+  modifier onlyActive {
+    require(started == true, "CCTF not started.");
+    _;
+  }
+
+  struct Flag {
+    address signer;
+    bool onlyFirstSolver;
+    uint256 points;
+    string skill_name;
+  }
+
+  mapping (address => Player) public players;
+  mapping (uint256 => Flag) public flags;
+
+  event CCTFStarted(uint256 timestamp);
+  event FlagAdded(uint256 indexed flagId, address flagSigner);
+  event FlagRemoved(uint256 indexed flagId);
+  event FlagSolved(uint256 indexed flagId, address indexed solver);
+
+  constructor(uint256 _volMaxPoints, uint256 _powDiff) {
+    admin = msg.sender;
+    volMaxPoints = _volMaxPoints;
+    powDiff = _powDiff;
+    started = false;
+  }
+  
+  function setAdmin(address _admin) external onlyAdmin {
+    require(_admin != address(0));
+    admin = _admin;
+  }
+
+  function setCCTFStatus(bool _started) external onlyAdmin {
+    started = _started;
+  }
+
+  function setFlag(uint256 _flagId, address _flagSigner, bool _onlyFirstSolver, uint256 _points, string memory _skill) external onlyAdmin{
+    flags[_flagId] = Flag(_flagSigner, _onlyFirstSolver, _points, _skill);
+    emit FlagAdded(_flagId, _flagSigner);
+  }
+
+  function setPowDiff(uint256 _powDiff) external onlyAdmin {
+    powDiff = _powDiff;
+  }
+
+
+  function register(string memory _RTFM) external {
+    require(players[msg.sender].status == PlayerStatus.Unverified, 'Already registered or banned');
+    //uint256 pow = uint256(keccak256(abi.encodePacked("CCTF", msg.sender,"registration", nonce)));
+    //require(pow < powDiff, "invalid pow");
+    require(keccak256(abi.encodePacked('I_read_it')) == keccak256(abi.encodePacked(_RTFM)));  // PoW can be used for harder challenges, this is Entry!
+    players[msg.sender].status = PlayerStatus.Verified;
+  }
+
+  function setPlayerStatus(address player, PlayerStatus status) external onlyAdmin {
+    players[player].status = status;
+  }
+  
+  
+////////// Submit flags
+    mapping(bytes32 => bool) usedNs;                       // Against replay attack (we only check message signer)
+    mapping (address => mapping (uint256 => bool)) Solves;     // address -> challenge ID -> solved/not
+    uint256 public submission_success_count = 0;               // For statistics
+
+    function SubmitFlag(bytes32 _message, bytes memory signature, uint256 _submitFor) external onlyActive {
+        require(players[msg.sender].status == PlayerStatus.Verified, "You are not even playing");
+        require(bytes32(_message).length <= 256, "Too long message.");
+        require(!usedNs[_message]);
+        usedNs[_message] = true;
+        require(recoverSigner(_message, signature) == flags[_submitFor].signer, "Not signed with the correct key.");
+        require(Solves[msg.sender][_submitFor] == false);
+        
+        Solves[msg.sender][_submitFor] = true;
+        players[msg.sender].points += flags[_submitFor].points;
+        players[msg.sender].points = players[msg.sender].points < volMaxPoints ? players[msg.sender].points : volMaxPoints;
+        
+        if (flags[_submitFor].onlyFirstSolver) {
+            flags[_submitFor].points = 0;
+        }
+        
+        submission_success_count = submission_success_count + 1;
+        emit FlagSolved(_submitFor, msg.sender);
+    }
+
+    function recoverSigner(bytes32 _ethSignedMessageHash, bytes memory _signature) public pure returns (address) {
+        (bytes32 r, bytes32 s, uint8 v) = splitSignature(_signature);
+        return ecrecover(_ethSignedMessageHash, v, r, s);
+    }
+
+    function splitSignature(bytes memory sig) public pure returns (bytes32 r, bytes32 s, uint8 v){
+        require(sig.length == 65, "Invalid signature length");
+        assembly {
+            r := mload(add(sig, 32))
+            s := mload(add(sig, 64))
+            v := byte(0, mload(add(sig, 96)))
+        }
+    }
+
+////////// Check status, scores, etc
+  function getPlayerStatus(address _player) external view returns (PlayerStatus) {
+    return players[_player].status;
+  }
+
+  function getPlayerPoints(address _player) external view returns (uint256) {
+    return players[_player].points < volMaxPoints ? players[_player].points : volMaxPoints;
+  } 
+
+  function getSuccessfulSubmissionCount() external view returns (uint256){
+      return submission_success_count;
+  }
+}