附件：
from ecdsa import SigningKey, NIST256p
import os
import random
key = SigningKey.generate(curve=NIST256p)
k = random.randrange(0, 2**256)
flag = os.getenv("GZCTF_FLAG") or "flag{fake_flag_for_testing}"
while True:
action = int(input("Input action (1 for sign, 2 for verify):"))
if action == 1:
text = input("Input message:")
signature = key.sign(("User message " + text).encode(), k=k)
print("Signature", signature.hex())
elif action == 2:
message = input("Enter message:")
signature = bytes.fromhex(input("Enter signature in hex:"))
if key.verifying_key.verify(signature, message.encode()):
print("Good signature")
if message == "Gimme flag":
print("Give you the flag")
print(flag)
exit()
ECDSA 是一种签名算法，它的计算过程，对于给定的消息 $m$，签名流程如下：
在本题中，随机数 $k$ 是不变的，意味着，如果拿到两次签名结果：
这里有两个未知数 $k, d_A$ 和两个方程，因此可以求解出私钥 $d_A$。有了私钥以后，就可以自己生成签名，从而得到 Flag 了。
攻击代码：
from pwn import *
from ecdsa import SigningKey, NIST256p
from ecdsa.keys import _truncate_and_convert_digest
from ecdsa.util import sigdecode_string
from hashlib import sha1
context(log_level="debug")
p = process(["python3", "main.py"])
# grab two signatures
texts = ["1", "2"]
sigs = []
hashes = []
for text in texts:
p.recvuntil(b"action")
p.sendline(b"1")
p.recvuntil(b"message")
p.sendline(text.encode())
p.recvuntil(b"Signature ")
sig = bytes.fromhex(p.recvline().decode())
r, s = sigdecode_string(sig, NIST256p.order)
sigs.append((r, s))
message = ("User message " + text).encode()
message_digest = sha1(message).digest()
h = _truncate_and_convert_digest(message_digest, NIST256p, True)
hashes.append(h)
# r1 = r2
assert sigs[0][0] == sigs[1][0]
# s1 = k^{-1} * (h1 + r1 * priv)
# s2 = k^{-1} * (h2 + r2 * priv)
# k = (s1 - s2)^{-1} * (h1 - h2)
k = (
pow(sigs[0][1] - sigs[1][1], -1, NIST256p.order)
* (hashes[0] - hashes[1])
% NIST256p.order
)
# priv = (s1*k - h1) * r1^{-1}
priv = (
(sigs[0][1] * k - hashes[0]) * pow(sigs[0][0], -1, NIST256p.order) % NIST256p.order
)
# forge signature
sk = SigningKey.from_secret_exponent(priv, NIST256p, hashfunc=sha1)
# get flag
p.recvuntil(b"action")
p.sendline(b"2")
p.recvuntil(b"message")
p.sendline(b"Gimme flag")
p.recvuntil(b"signature")
p.sendline(sk.sign(b"Gimme flag").hex().encode())
p.recvall()
注意这里用到的 ecdsa 库是纯 python 实现的，不抗时间侧信道攻击，因此不建议在生产环境中使用。
下面是使用 Qwen Code + DeepSeek 自动求解的过程：
{'role': 'user', 'parts': [{'text': 'Solve CTF challenge. The remote is at ctf.jia.je:32789. You can use pwntools and ecdsa directly.'}]}
{'role': 'model', 'parts': [{'text': "I need to solve a CTF challenge. First, I need to examine the existing main.py to see what's there, then connect to the remote service and understand the challenge. Let me start by reading the main.py file.", 'thought': True}, {'functionCall': {'id': 'call_00_PplE61EBd6AsWUExqHb0VoEM', 'name': 'read_file', 'args': {'absolute_path': '/home/jiegec/ctf/temp/main.py'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_PplE61EBd6AsWUExqHb0VoEM', 'name': 'read_file', 'response': {'output': 'from ecdsa import SigningKey, NIST256p\nimport os\nimport random\n\nkey = SigningKey.generate(curve=NIST256p)\nk = random.randrange(0, 2**256)\nflag = os.getenv("GZCTF_FLAG") or "flag{fake_flag_for_testing}"\n\nwhile True:\n action = int(input("Input action (1 for sign, 2 for verify):"))\n if action == 1:\n text = input("Input message:")\n signature = key.sign(("User message " + text).encode(), k=k)\n print("Signature", signature.hex())\n elif action == 2:\n message = input("Enter message:")\n signature = bytes.fromhex(input("Enter signature in hex:"))\n if key.verifying_key.verify(signature, message.encode()):\n print("Good signature")\n if message == "Gimme flag":\n print("Give you the flag")\n print(flag)\n exit()\n'}}}]}
{'role': 'model', 'parts': [{'text': 'Now I understand the challenge. It\'s an ECDSA signature challenge with a nonce k reused? Let\'s analyze: The server uses a SigningKey (private key unknown). It generates a random k once at the start (k = random.randrange(0, 2**256)). Then it loops, allowing two actions: sign and verify. In sign action, it signs "User message " + text with the same k each time? Wait: The k is generated once at the start, but in the sign function they pass k=k, which is the same k each time? Actually, the sign method of ecdsa library can accept a deterministic k (if you pass k parameter). They pass the same k each time because k is defined globally and not changed. So the same k is reused for all signatures. That\'s a vulnerability: if we can get two signatures with the same k, we can recover the private key.\n\nWe need to get the flag by verifying a signature for message "Gimme flag". We need to produce a valid signature for that message without knowing the private key. Since we can request signatures for arbitrary messages (prefixed with "User message "), we can maybe perform a chosen message attack.\n\nLet\'s think: The signature scheme is ECDSA over NIST256p. The signer uses deterministic k (same across all signatures). The formula: r = (k * G).x mod n, s = k^{-1}(H(m) + r * d) mod n, where d is private key.\n\nIf we have two signatures (r1, s1) and (r2, s2) for messages m1 and m2 with same k, then r1 = r2 (since r depends only on k). So we can compute k = (H(m1) - H(m2)) / (s1 - s2) mod n? Actually, we can derive d.\n\nStandard ECDSA nonce reuse attack: Given two signatures (r, s1) and (r, s2) for messages m1 and m2, we have:\n\ns1 = k^{-1}(H(m1) + r*d) mod n\ns2 = k^{-1}(H(m2) + r*d) mod n\n\nSubtract: s1 - s2 = k^{-1}(H(m1) - H(m2)) mod n\n\nThus k = (H(m1) - H(m2)) * (s1 - s2)^{-1} mod n\n\nOnce we have k, we can compute d = (s1*k - H(m1)) * r^{-1} mod n.\n\nThen we can sign any message ourselves, including "Gimme flag".\n\nBut we need to consider the prefix "User message " added to the text we input. The sign action uses ("User message " + text).encode(). So we can choose text such that the full message is something we can compute hash for. We\'ll need to compute the hash of "User message " + text.\n\nWe also need to know the curve parameters (NIST256p) and the hash function used (likely SHA256). ECDSA with NIST256p uses SHA256.\n\nNow we need to write a solution script using pwntools. First, let\'s check if pwntools and ecdsa are installed. We can run a quick shell command to see. Let\'s also create a todo list to track steps.', 'thought': True}, {'functionCall': {'id': 'call_00_340zWOwH25uoWnG3Vlv4ekir', 'name': 'todo_write', 'args': {'todos': [{'id': '1', 'content': 'Examine main.py and understand the vulnerability', 'status': 'completed'}, {'id': '2', 'content': 'Write exploit script to connect to remote service', 'status': 'pending'}, {'id': '3', 'content': 'Collect two signatures with same k', 'status': 'pending'}, {'id': '4', 'content': 'Compute private key using nonce reuse', 'status': 'pending'}, {'id': '5', 'content': "Sign 'Gimme flag' message", 'status': 'pending'}, {'id': '6', 'content': 'Verify and get flag', 'status': 'pending'}]}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_340zWOwH25uoWnG3Vlv4ekir', 'name': 'todo_write', 'response': {'output': 'Todos have been modified successfully. Ensure that you continue to use the todo list to track your progress. Please proceed with the current tasks if applicable\n\n<system-reminder>\nYour todo list has changed. DO NOT mention this explicitly to the user. Here are the latest contents of your todo list: \n\n[{"id":"1","content":"Examine main.py and understand the vulnerability","status":"completed"},{"id":"2","content":"Write exploit script to connect to remote service","status":"pending"},{"id":"3","content":"Collect two signatures with same k","status":"pending"},{"id":"4","content":"Compute private key using nonce reuse","status":"pending"},{"id":"5","content":"Sign \'Gimme flag\' message","status":"pending"},{"id":"6","content":"Verify and get flag","status":"pending"}]. Continue on with the tasks at hand if applicable.\n</system-reminder>'}}}]}
{'role': 'model', 'parts': [{'text': "Now I'll write the exploit script. First, let's check if pwntools is installed and we can import. Let's run a quick Python to see. But I'll just write the script and test locally first. We need to simulate the server locally to verify our exploit works. We can run the main.py locally with a fake flag. Let's start by running the main.py in background and connect to it via netcat? Or we can directly import the main.py? Better to write a test script that interacts with a subprocess.\n\nBut first, let's create a directory for our exploit script. Let's list the current directory to see if there are other files.", 'thought': True}, {'functionCall': {'id': 'call_00_Wq9Gj7HaKmJrSlhNTWibYatH', 'name': 'list_directory', 'args': {'path': '/home/jiegec/ctf/temp'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_Wq9Gj7HaKmJrSlhNTWibYatH', 'name': 'list_directory', 'response': {'output': 'Directory listing for /home/jiegec/ctf/temp:\nmain.py'}}}]}
{'role': 'model', 'parts': [{'text': "Only main.py. Let's create exploit.py. Let's start writing. First, I'll need to import necessary libraries: pwn, ecdsa, hashlib, etc. Let's also update todo.", 'thought': True}, {'functionCall': {'id': 'call_00_tvfvKkOrvJWnlpJb9rO6r2hV', 'name': 'todo_write', 'args': {'todos': [{'id': '1', 'content': 'Examine main.py and understand the vulnerability', 'status': 'completed'}, {'id': '2', 'content': 'Write exploit script to connect to remote service', 'status': 'in_progress'}, {'id': '3', 'content': 'Collect two signatures with same k', 'status': 'pending'}, {'id': '4', 'content': 'Compute private key using nonce reuse', 'status': 'pending'}, {'id': '5', 'content': "Sign 'Gimme flag' message", 'status': 'pending'}, {'id': '6', 'content': 'Verify and get flag', 'status': 'pending'}]}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_tvfvKkOrvJWnlpJb9rO6r2hV', 'name': 'todo_write', 'response': {'output': 'Todos have been modified successfully. Ensure that you continue to use the todo list to track your progress. Please proceed with the current tasks if applicable\n\n<system-reminder>\nYour todo list has changed. DO NOT mention this explicitly to the user. Here are the latest contents of your todo list: \n\n[{"id":"1","content":"Examine main.py and understand the vulnerability","status":"completed"},{"id":"2","content":"Write exploit script to connect to remote service","status":"in_progress"},{"id":"3","content":"Collect two signatures with same k","status":"pending"},{"id":"4","content":"Compute private key using nonce reuse","status":"pending"},{"id":"5","content":"Sign \'Gimme flag\' message","status":"pending"},{"id":"6","content":"Verify and get flag","status":"pending"}]. Continue on with the tasks at hand if applicable.\n</system-reminder>'}}}]}
{'role': 'model', 'parts': [{'text': "Now write the exploit script. Let's create a new file. I'll use write_file. First, I need to know the absolute path: /home/jiegec/ctf/temp/exploit.py. Let's write. I'll include comments and steps. We'll also need to compute modular inverses. Use Python's pow with -1 mod n. Let's get curve parameters: ecdsa.NIST256p.generator, .order, .curve.\n\nLet's start with a skeleton. We'll also include a local test function. Let's do it.", 'thought': True}, {'functionCall': {'id': 'call_00_EDBtDvXcFkNgKOF0fcig1gqY', 'name': 'write_file', 'args': {'file_path': '/home/jiegec/ctf/temp/exploit.py', 'content': '#!/usr/bin/env python3\nimport sys\nsys.path.insert(0, \'.\') # ensure we can import ecdsa if not installed globally\n\nfrom pwn import *\nfrom ecdsa import SigningKey, NIST256p, VerifyingKey\nimport hashlib\nimport binascii\n\n# Curve parameters\ncurve = NIST256p\nn = curve.order\nG = curve.generator\n\ndef hash_msg(msg: bytes) -> int:\n """Compute SHA256 hash of message and convert to integer."""\n h = hashlib.sha256(msg).digest()\n return int.from_bytes(h, \'big\') % n\n\ndef recover_private_key(r, s1, s2, h1, h2):\n """\n Given two signatures (r, s1) and (r, s2) for messages with hashes h1, h2,\n recover the private key d.\n """\n # Compute k = (h1 - h2) * (s1 - s2)^-1 mod n\n s_diff = (s1 - s2) % n\n s_diff_inv = pow(s_diff, -1, n)\n k = ((h1 - h2) * s_diff_inv) % n\n # Compute d = (s1 * k - h1) * r^-1 mod n\n r_inv = pow(r, -1, n)\n d = ((s1 * k - h1) * r_inv) % n\n return d, k\n\ndef exploit(remote_host, remote_port):\n """Connect to remote service and extract flag."""\n log.info(f"Connecting to {remote_host}:{remote_port}")\n io = remote(remote_host, remote_port)\n \n # Step 1: Get two signatures for different messages but same k\n # We can send any text; the server will prepend "User message "\n # Choose two distinct texts\n text1 = "A"\n text2 = "B"\n \n # Request signature for text1\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"1")\n io.sendlineafter(b"Input message:", text1.encode())\n io.recvuntil(b"Signature ")\n sig1_hex = io.recvline().strip().decode()\n sig1 = bytes.fromhex(sig1_hex)\n log.success(f"Got signature 1: {sig1_hex}")\n \n # Request signature for text2\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"1")\n io.sendlineafter(b"Input message:", text2.encode())\n io.recvuntil(b"Signature ")\n sig2_hex = io.recvline().strip().decode()\n sig2 = bytes.fromhex(sig2_hex)\n log.success(f"Got signature 2: {sig2_hex}")\n \n # Parse signatures (r, s)\n # ECDSA signatures are DER encoded? Actually, ecdsa library uses simple r||s?\n # Let\'s examine the signature format: In ecdsa library, signature is bytes of length 64? \n # For NIST256p, signature is 64 bytes (r and s each 32 bytes).\n if len(sig1) == 64:\n r1 = int.from_bytes(sig1[:32], \'big\')\n s1 = int.from_bytes(sig1[32:], \'big\')\n r2 = int.from_bytes(sig2[:32], \'big\')\n s2 = int.from_bytes(sig2[32:], \'big\')\n else:\n # Maybe DER encoded; we\'ll need to decode\n # For now assume raw 64 bytes\n log.error("Unexpected signature length")\n return\n \n # Ensure r1 == r2 (same k)\n if r1 != r2:\n log.error("r values differ; k not reused?")\n return\n \n r = r1\n # Compute hashes of the signed messages\n msg1 = ("User message " + text1).encode()\n msg2 = ("User message " + text2).encode()\n h1 = hash_msg(msg1)\n h2 = hash_msg(msg2)\n \n # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n \n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # We need to produce a signature using the same k? Actually we can sign with any k.\n # But we can use the recovered private key to sign properly.\n # Create a signing key object from d\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n # Sign the target message with a random k (or we can reuse k if we want)\n # Use deterministic ECDSA (default) or we can specify k.\n signature = sk.sign(target_msg, k=k) # use same k for simplicity\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")\n \n # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n \n # Receive response\n resp = io.recvall(timeout=2).decode()\n log.info(f"Response: {resp}")\n # Flag should be printed\n io.close()\n return resp\n\nif __name__ == "__main__":\n # Test locally first\n import subprocess\n import time\n import os\n \n log.info("Starting local test...")\n # Set fake flag\n env = os.environ.copy()\n env["GZCTF_FLAG"] = "flag{test_flag}"\n # Start server process\n proc = subprocess.Popen([sys.executable, "main.py"], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=env)\n time.sleep(0.5)\n # We\'ll run exploit against localhost:? Actually the server is stdin/stdout, not network.\n # For simplicity, we\'ll just test the recovery logic separately.\n # Let\'s instead write a unit test using the ecdsa library.\n log.info("Local test skipped; proceeding to remote.")\n \n # Remote target\n host = "ctf.jia.je"\n port = 32789\n result = exploit(host, port)\n print(result)'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_EDBtDvXcFkNgKOF0fcig1gqY', 'name': 'write_file', 'response': {'output': 'Successfully created and wrote to new file: /home/jiegec/ctf/temp/exploit.py.'}}}]}
{'role': 'model', 'parts': [{'text': "Now I need to verify the signature format. In ecdsa library, the signature returned by `sign` method is a DER-encoded signature? Actually, looking at the ecdsa documentation: `sign` returns a DER-encoded signature by default, but if you pass `sigencode` parameter you can get raw r and s. In the main.py they print signature.hex() where signature is the result of `key.sign(...)`. Let's check the default encoding. The ecdsa library's default signature encoding is DER? I think the default is DER. Let's quickly write a small test to see the length. We can run a quick Python snippet. Let's do it via shell.", 'thought': True}, {'functionCall': {'id': 'call_00_HTntOdKL0ZMf97kQMa7chwop', 'name': 'run_shell_command', 'args': {'command': 'cd /home/jiegec/ctf/temp && python3 -c "from ecdsa import SigningKey, NIST256p; import random; key = SigningKey.generate(curve=NIST256p); k = random.randrange(0, 2**256); sig = key.sign(b\'test\', k=k); print(len(sig), sig.hex())"', 'is_background': False}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_HTntOdKL0ZMf97kQMa7chwop', 'name': 'run_shell_command', 'response': {'output': 'Command: cd /home/jiegec/ctf/temp && python3 -c "from ecdsa import SigningKey, NIST256p; import random; key = SigningKey.generate(curve=NIST256p); k = random.randrange(0, 2**256); sig = key.sign(b\'test\', k=k); print(len(sig), sig.hex())"\nDirectory: (root)\nOutput: 64 83be5207da4951ce39ca398480637ad6faa54c5e84ff666ec93beb50971f86d1f269f7685e86b02a024ac8e5084a0e7a28212cff1a3b580e3ac28a10aa6a0269\nError: (none)\nExit Code: 0\nSignal: (none)\nBackground PIDs: 2046784\nProcess Group PGID: (none)'}}}]}
{'role': 'model', 'parts': [{'text': "Great! The signature length is 64 bytes (raw r and s concatenated). That's convenient. So we can parse as 32 bytes r and 32 bytes s.\n\nNow we need to ensure that the same k is used across signatures. In the main.py, k is generated once and reused for each sign call (since they pass k=k). Indeed, k is not regenerated. So nonce reuse.\n\nNow we need to test our exploit locally. We can run the main.py as a subprocess and interact with it via pipes. Let's write a local test that simulates the server interaction. We'll create a function that runs the server in a subprocess and communicates with it via stdin/stdout. Then we can test our exploit logic.\n\nBut first, let's update todo. Let's mark step 2 as completed and move to step 3.", 'thought': True}, {'functionCall': {'id': 'call_00_iam22TZBnKazqobQW7FTolj6', 'name': 'todo_write', 'args': {'todos': [{'id': '1', 'content': 'Examine main.py and understand the vulnerability', 'status': 'completed'}, {'id': '2', 'content': 'Write exploit script to connect to remote service', 'status': 'completed'}, {'id': '3', 'content': 'Collect two signatures with same k', 'status': 'in_progress'}, {'id': '4', 'content': 'Compute private key using nonce reuse', 'status': 'pending'}, {'id': '5', 'content': "Sign 'Gimme flag' message", 'status': 'pending'}, {'id': '6', 'content': 'Verify and get flag', 'status': 'pending'}]}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_iam22TZBnKazqobQW7FTolj6', 'name': 'todo_write', 'response': {'output': 'Todos have been modified successfully. Ensure that you continue to use the todo list to track your progress. Please proceed with the current tasks if applicable\n\n<system-reminder>\nYour todo list has changed. DO NOT mention this explicitly to the user. Here are the latest contents of your todo list: \n\n[{"id":"1","content":"Examine main.py and understand the vulnerability","status":"completed"},{"id":"2","content":"Write exploit script to connect to remote service","status":"completed"},{"id":"3","content":"Collect two signatures with same k","status":"in_progress"},{"id":"4","content":"Compute private key using nonce reuse","status":"pending"},{"id":"5","content":"Sign \'Gimme flag\' message","status":"pending"},{"id":"6","content":"Verify and get flag","status":"pending"}]. Continue on with the tasks at hand if applicable.\n</system-reminder>'}}}]}
{'role': 'model', 'parts': [{'text': "Now, let's write a local test script that actually interacts with the server (main.py) and verifies our attack works. We'll create a separate test file, or modify exploit.py to include a proper local test. Let's do that now. We'll also need to ensure we compute hashes correctly. The hash function used by ecdsa is SHA256. The hash is of the message bytes. The integer is the leftmost bits of hash modulo n? Actually, ecdsa library uses hashfunc parameter; default is SHA256. In main.py they didn't specify, so default SHA256. We'll use SHA256.\n\nNow we need to be careful about the message encoding: they use .encode() which defaults to UTF-8. That's fine.\n\nLet's create a test that runs main.py as subprocess and communicates via stdin/stdout. We'll write a helper class. Let's first update exploit.py with a proper local test. We'll replace the existing test section.\n\nBut before that, let's run a quick check to see if pwntools is installed. Let's run a Python import. Let's do a shell command.", 'thought': True}, {'functionCall': {'id': 'call_00_SbhniJZrockQTc5qGK4QjTZY', 'name': 'run_shell_command', 'args': {'command': 'cd /home/jiegec/ctf/temp && python3 -c "import pwn; print(pwn.__version__)" 2>&1', 'is_background': False}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_SbhniJZrockQTc5qGK4QjTZY', 'name': 'run_shell_command', 'response': {'output': 'Command: cd /home/jiegec/ctf/temp && python3 -c "import pwn; print(pwn.__version__)" 2>&1\nDirectory: (root)\nOutput: Traceback (most recent call last):\n File "<string>", line 1, in <module>\n import pwn; print(pwn.__version__)\n ^^^^^^^^^^^^^^^\nAttributeError: module \'pwn\' has no attribute \'__version__\'\nError: (none)\nExit Code: 1\nSignal: (none)\nBackground PIDs: 2047445\nProcess Group PGID: (none)'}}}]}
{'role': 'model', 'parts': [{'text': 'It imported successfully', 'thought': True}]}
{'role': 'user', 'parts': [{'text': 'Do not check pwn.__version__. Use it directly.'}]}
{'role': 'model', 'parts': [{'text': 'The user wants me to just use pwntools without checking version. Let me run the exploit script directly. First, I should ensure the script can import pwntools. Let me run it.', 'thought': True}, {'functionCall': {'id': 'call_00_fOc1NWZsxuIDokcZTOPT5CIH', 'name': 'run_shell_command', 'args': {'command': 'cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1', 'is_background': False}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_fOc1NWZsxuIDokcZTOPT5CIH', 'name': 'run_shell_command', 'response': {'output': "Command: cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1\nDirectory: (root)\nOutput: [*] Starting local test...\n[*] Local test skipped; proceeding to remote.\n[*] Connecting to ctf.jia.je:32789\n[x] Opening connection to ctf.jia.je on port 32789\n[x] Opening connection to ctf.jia.je on port 32789: Trying 172.238.22.117\n[+] Opening connection to ctf.jia.je on port 32789: Done\n[+] Got signature 1: 91e6c7ec4f68f75679d2ad767020192bf335529fdc001ce51227819728d01e3b2563814ced54cee0f9c6e405e69adef82fadd2d481ea8e88bf4dc45bbf6cdd3d\n[+] Got signature 2: 91e6c7ec4f68f75679d2ad767020192bf335529fdc001ce51227819728d01e3b11f7e6425c496417aad1be27af5f400a05ff245e86c55101484ffde34232350a\n[+] Recovered private key: 0x8d088c1c334d4e3e187afb88af875b51bd83211df1cf803ff7ee3a4e1f7e0ec7\n[+] Recovered nonce k: 0xf5b541eafa32ca81d1ebeae4def398557361f0be199edc3f9ee3f34791f56266\n[+] Forged signature for 'Gimme flag': 912227f0f9ce00360ba6dccf5e603d31394fa98c63a86f2354e03bbe82849e9a458b51030452178f0167062b31cd7b22ba4d6f8a50868757314277a9d4f6850a\n[x] Receiving all data\n[x] Receiving all data: 0B\n[+] Receiving all data: Done (0B)\n[*] Closed connection to ctf.jia.je port 32789\n[*] Response:\nError: (none)\nExit Code: 0\nSignal: (none)\nBackground PIDs: 2047524\nProcess Group PGID: (none)"}}}]}
{'role': 'model', 'parts': [{'text': 'The exploit ran but got no response. It seems the connection closed after sending the verification request. Let me examine the exploit script: it uses `io.recvall(timeout=2)`. The server might print "Good signature" and then "Give you the flag" and the flag, but we didn\'t capture it because the server may have exited after printing the flag? Wait, the server code prints "Give you the flag" and then prints flag and exits. The connection would close. The `recvall` should have captured everything until EOF. However, we got 0 bytes. Possibly the verification failed? Let me check the signature verification logic. We used the same k to sign "Gimme flag". But the server\'s verifying key expects a signature made with the original private key, but we used the recovered private key, that\'s fine. However, we used the same k that we recovered (which was used for signing "User message A" and "User message B"). That should produce a valid signature.\n\nBut we need to ensure the signature format matches what the server expects. The server uses `key.verifying_key.verify(signature, message.encode())`. The ecdsa library\'s `verify` expects a signature in the same format as produced by `sign`. That is, a 64-byte raw r||s concatenation. Our signature is 64 bytes. It should verify.\n\nMaybe we need to use deterministic signing (i.e., not specify k) because the server will verify with the public key, not caring about k. Actually, we can sign with any k, as long as the signature is valid. Using the same k we recovered is fine.\n\nLet me add debug prints to see what\'s happening. Also, we should handle the interaction more carefully: after sending the verification request, we need to read lines. Let me modify the exploit script to print more info. First, let me update the exploit script. Let\'s also test locally with a mock server. Let\'s write a quick test to ensure our recovery works. Let me do that now.', 'thought': True}, {'functionCall': {'id': 'call_00_ACKfJ22lhTMZAxwf0olwlJAq', 'name': 'edit', 'args': {'file_path': '/home/jiegec/ctf/temp/exploit.py', 'old_string': ' # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n \n # Receive response\n resp = io.recvall(timeout=2).decode()\n log.info(f"Response: {resp}")\n # Flag should be printed\n io.close()\n return resp', 'new_string': ' # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n \n # Receive response line by line\n try:\n line1 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line1: {line1}")\n if line1 == "Good signature":\n line2 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line2: {line2}")\n if line2 == "Give you the flag":\n line3 = io.recvline(timeout=1).decode().strip()\n log.success(f"Flag: {line3}")\n io.close()\n return line3\n except EOFError:\n log.error("Connection closed unexpectedly")\n # Fallback: try to receive all data\n try:\n resp = io.recvall(timeout=2).decode()\n log.info(f"Response: {resp}")\n except:\n pass\n io.close()\n return None'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_ACKfJ22lhTMZAxwf0olwlJAq', 'name': 'edit', 'response': {'output': 'The file: /home/jiegec/ctf/temp/exploit.py has been updated. Showing lines 105-135 of 155 from the edited file:\n\n---\n\n # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n\n # Receive response line by line\n try:\n line1 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line1: {line1}")\n if line1 == "Good signature":\n line2 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line2: {line2}")\n if line2 == "Give you the flag":\n line3 = io.recvline(timeout=1).decode().strip()\n log.success(f"Flag: {line3}")\n io.close()\n return line3\n except EOFError:\n log.error("Connection closed unexpectedly")\n # Fallback: try to receive all data\n try:\n resp = io.recvall(timeout=2).decode()\n log.info(f"Response: {resp}")\n except:\n pass\n io.close()\n return None\n\nif __name__ == "__main__":\n # Test locally first\n import subprocess'}}}]}
{'role': 'model', 'parts': [{'text': "Now let's run again. Let me also add a check to see if the signatures are valid before sending. Let's compute verification locally. Let me add a quick verification step. But first, run the updated exploit.", 'thought': True}, {'functionCall': {'id': 'call_00_bnK5dubhS0JFQsIYNVTT0V5T', 'name': 'run_shell_command', 'args': {'command': 'cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1', 'is_background': False}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_bnK5dubhS0JFQsIYNVTT0V5T', 'name': 'run_shell_command', 'response': {'output': 'Command: cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1\nDirectory: (root)\nOutput: [*] Starting local test...\n[*] Local test skipped; proceeding to remote.\n[*] Connecting to ctf.jia.je:32789\n[x] Opening connection to ctf.jia.je on port 32789\n[x] Opening connection to ctf.jia.je on port 32789: Trying 172.238.22.117\n[+] Opening connection to ctf.jia.je on port 32789: Done\n[+] Got signature 1: 587f2a4503e344e36146985c1dfc7d4eda2543cda7806b1cdf8b7f901a398e240368282617efeae0b6e5227ee5276c4d02c7d150d9ebc265b75850a3aaa36d45\n[+] Got signature 2: 587f2a4503e344e36146985c1dfc7d4eda2543cda7806b1cdf8b7f901a398e246ec266f31868e025b1bc3ebe38dafd28a8cba76687442978699d0c57682a672e\n[+] Recovered private key: 0x2ce241b0aa4417349a3b68a17fa4b4637b9d4e3e29ad525ac229b5231bc9e992\n[+] Recovered nonce k: 0x7228cdeeb7e5656d2e4d7cf69cd0563611b48d98bccf935fd4b256742d629b06\n[+] Forged signature for \'Gimme flag\': 7217cc84ba9895ed5f88398e349876e44a5ee32689b14e5e014d86f60c7109dd5d2074b56663c1581882a2af1c9d0ac077064cf756a77104f4873d2fdff25896\n[ERROR] Connection closed unexpectedly\nTraceback (most recent call last):\n File "/home/jiegec/ctf/temp/exploit.py", line 112, in exploit\n line1 = io.recvline(timeout=1).decode().strip()\n ~~~~~~~~~~~^^^^^^^^^^^\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/tube.py", line 527, in recvline\n return self.recvuntil(self.newline, drop = not keepends, timeout = timeout)\n ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/tube.py", line 341, in recvuntil\n res = self.recv(timeout=self.timeout)\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/tube.py", line 106, in recv\n return self._recv(numb, timeout) or b\'\'\n ~~~~~~~~~~^^^^^^^^^^^^^^^\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/tube.py", line 176, in _recv\n if not self.buffer and not self._fillbuffer(timeout):\n ~~~~~~~~~~~~~~~~^^^^^^^^^\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/tube.py", line 155, in _fillbuffer\n data = self.recv_raw(self.buffer.get_fill_size())\n File "/usr/lib/python3/dist-packages/pwnlib/tubes/sock.py", line 56, in recv_raw\n raise EOFError\nEOFError\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File "/home/jiegec/ctf/temp/exploit.py", line 154, in <module>\n result = exploit(host, port)\n File "/home/jiegec/ctf/temp/exploit.py", line 123, in exploit\n log.error("Connection closed unexpectedly")\n ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/usr/lib/python3/dist-packages/pwnlib/log.py", line 439, in error\n raise PwnlibException(message % args)\npwnlib.exception.PwnlibException: Connection closed unexpectedly\n[*] Closed connection to ctf.jia.je port 32789\nError: (none)\nExit Code: 1\nSignal: (none)\nBackground PIDs: 2047817\nProcess Group PGID: (none)'}}}]}
{'role': 'model', 'parts': [{'text': 'The connection closed after sending verification. That suggests the signature verification failed and the server closed connection (maybe no output). Wait, the server prints "Good signature" if verification succeeds, otherwise it prints nothing? The code shows: `if key.verifying_key.verify(signature, message.encode()): print("Good signature")`. If verification fails, there\'s no print and the loop continues? Actually, the server is in a `while True:` loop, after verification it prints "Good signature" and then checks if message == "Gimme flag". If verification fails, it prints nothing and loops again? Wait, the server reads action again. So if verification fails, it prints nothing and goes back to reading action. But the connection is still open. However, the server might close connection on error? Not in the code.\n\nOur connection closed because we didn\'t receive anything, maybe the server expects a newline after the signature hex? Let\'s examine the server\'s input reading: `signature = bytes.fromhex(input("Enter signature in hex:"))`. The `input()` reads a line, strips newline. That\'s fine.\n\nBut after verification fails, the server loops again and expects a new action integer. However, we didn\'t send anything, so the server\'s `input()` will block waiting for input. The connection shouldn\'t close. But the server might be closing connection due to some other reason (maybe the remote service closes after each request?). Actually, the server is a single-threaded loop, it stays open. However, the remote might be killing connections after a few requests? Not sure.\n\nLet\'s add more debugging: let\'s capture the interaction step by step with a test that prints what we send and receive. Let me write a simple test script that uses pwntools interactively. But first, let me examine the signatures more closely. The r values are same? Let\'s check: signature 1 first 32 bytes hex: 587f2a4503e344e36146985c1dfc7d4eda2543cda7806b1cdf8b7f901a398e24, and second signature first 32 bytes: 587f2a4503e344e36146985c1dfc7d4eda2543cda7806b1cdf8b7f901a398e24. Yes, same r. Good.\n\nNow we need to verify that the recovered private key is correct. Let\'s compute the public key from the private key and compare with the server\'s public key? We don\'t have the public key. But we can verify by signing a test message and asking the server to verify it (with a different action). That would be a good test.\n\nLet\'s modify the exploit: after recovering private key, we can sign a random message and ask the server to verify (with action 2). If it says "Good signature", then we know the private key is correct. Then we can sign "Gimme flag". Let\'s do that.\n\nAlso, we should ensure we\'re using the correct hash function. The ecdsa library uses SHA256 by default? Actually, the `sign` method uses a hash function; default is SHA1? Let\'s check: In ecdsa library, the `sign` method uses the hash function specified when creating the signing key? The default is SHA1. But the server\'s `sign` call uses `key.sign(("User message " + text).encode(), k=k)`. The default hash function is SHA1. However, the `verify` method also uses SHA1 by default. That\'s consistent. However, our hash_msg uses SHA256. That\'s wrong! We need to use SHA1. Let\'s fix that.\n\nIndeed, the ecdsa library default hash is hashlib.sha1. Let\'s check: In ecdsa package, `SigningKey.sign` uses `hashfunc` parameter default is `hashlib.sha1`. That\'s important. So we must compute SHA1 hash, not SHA256.\n\nLet\'s update the hash_msg function to use SHA1. Also, the order n is curve order. Let\'s modify.\n\nLet me update the exploit script. First, let\'s create a new version. Let\'s also add a verification test. Let me edit the file.', 'thought': True}, {'functionCall': {'id': 'call_00_dvmZf51PwNuI50STBaQqGm4H', 'name': 'edit', 'args': {'file_path': '/home/jiegec/ctf/temp/exploit.py', 'old_string': 'def hash_msg(msg: bytes) -> int:\n """Compute SHA256 hash of message and convert to integer."""\n h = hashlib.sha256(msg).digest()\n return int.from_bytes(h, \'big\') % n', 'new_string': 'def hash_msg(msg: bytes) -> int:\n """Compute SHA1 hash of message and convert to integer (default hash for ecdsa)."""\n h = hashlib.sha1(msg).digest()\n return int.from_bytes(h, \'big\') % n'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_dvmZf51PwNuI50STBaQqGm4H', 'name': 'edit', 'response': {'output': 'The file: /home/jiegec/ctf/temp/exploit.py has been updated. Showing lines 12-21 of 155 from the edited file:\n\n---\n\nn = curve.order\nG = curve.generator\n\ndef hash_msg(msg: bytes) -> int:\n """Compute SHA1 hash of message and convert to integer (default hash for ecdsa)."""\n h = hashlib.sha1(msg).digest()\n return int.from_bytes(h, \'big\') % n\n\ndef recover_private_key(r, s1, s2, h1, h2):\n """'}}}]}
{'role': 'model', 'parts': [{'text': 'Now we also need to ensure the verification test. Let me add a step to verify the recovered key. I\'ll modify the exploit function after recovering private key. Let\'s do a quick test: sign a random message and send to server for verification. If verification passes, we know the key is correct.\n\nLet me edit the exploit function. I\'ll insert after recovering private key and before signing "Gimme flag". Let\'s find that section. Let me read the file to see the structure. Let\'s use read_file.', 'thought': True}, {'functionCall': {'id': 'call_00_VXYt6dkyvqwTClxZnRM6ughw', 'name': 'read_file', 'args': {'absolute_path': '/home/jiegec/ctf/temp/exploit.py', 'offset': 80, 'limit': 40}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_VXYt6dkyvqwTClxZnRM6ughw', 'name': 'read_file', 'response': {'output': 'Showing lines 81-120 of 155 total lines.\n\n---\n\n r = r1\n # Compute hashes of the signed messages\n msg1 = ("User message " + text1).encode()\n msg2 = ("User message " + text2).encode()\n h1 = hash_msg(msg1)\n h2 = hash_msg(msg2)\n\n # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n\n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # We need to produce a signature using the same k? Actually we can sign with any k.\n # But we can use the recovered private key to sign properly.\n # Create a signing key object from d\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n # Sign the target message with a random k (or we can reuse k if we want)\n # Use deterministic ECDSA (default) or we can specify k.\n signature = sk.sign(target_msg, k=k) # use same k for simplicity\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")\n\n # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n\n # Receive response line by line\n try:\n line1 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line1: {line1}")\n if line1 == "Good signature":\n line2 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line2: {line2}")\n if line2 == "Give you the flag":\n line3 = io.recvline(timeout=1).decode().strip()\n log.success(f"Flag: {line3}")\n io.close()'}}}]}
{'role': 'model', 'parts': [{'text': 'Now I\'ll add a verification test before signing "Gimme flag". Let me edit that section. Let\'s replace from "Now sign \'Gimme flag\'" to before that. Let me write the new code. First, let\'s compute the verification step. Let\'s sign a test message "test" and ask the server to verify. If verification passes, we continue. If not, we can try to compute the correct private key maybe using alternative formula (since we might have miscomputed due to hash mismatch). We already fixed hash to SHA1. Let\'s also ensure we\'re using the correct formula. The standard ECDSA nonce reuse attack formula is: k = (h1 - h2) * (s1 - s2)^-1 mod n, d = (s1*k - h1) * r^-1 mod n. That\'s what we have.\n\nLet\'s also verify that the recovered private key matches the public key? We can compute the verifying key from d and compare with the server\'s verifying key? We don\'t have it. But we can ask the server to verify a signature we produce with that key.\n\nLet\'s edit the file. Let me replace lines from "Now sign \'Gimme flag\'..." to before the verification request. Let\'s do it step by step. Let me write the new block. Let\'s also add more logging. Let\'s use edit. First, let me capture the exact old_string from line 98 to line 112 (just before the verification request). Let me view more lines. Let\'s read from line 90 to 120. Let me do a quick read_many_files with offset. Actually easier: use read_file with appropriate offset. Let\'s get the exact lines. Let me compute: line numbers approximate. Let\'s get from "Now sign \'Gimme flag\' with the private key" to "sig_hex = signature.hex()". Let\'s do that now.', 'thought': True}, {'functionCall': {'id': 'call_00_1ODdshmWVbQl1HfOZf6QmmVm', 'name': 'read_file', 'args': {'absolute_path': '/home/jiegec/ctf/temp/exploit.py', 'offset': 95, 'limit': 20}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_1ODdshmWVbQl1HfOZf6QmmVm', 'name': 'read_file', 'response': {'output': 'Showing lines 96-115 of 155 total lines.\n\n---\n\n # But we can use the recovered private key to sign properly.\n # Create a signing key object from d\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n # Sign the target message with a random k (or we can reuse k if we want)\n # Use deterministic ECDSA (default) or we can specify k.\n signature = sk.sign(target_msg, k=k) # use same k for simplicity\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")\n\n # Send verify request\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", target_msg)\n io.sendlineafter(b"Enter signature in hex:", sig_hex.encode())\n\n # Receive response line by line\n try:\n line1 = io.recvline(timeout=1).decode().strip()\n log.info(f"Line1: {line1}")\n if line1 == "Good signature":\n line2 = io.recvline(timeout=1).decode().strip()'}}}]}
{'role': 'model', 'parts': [{'text': 'Now I\'ll replace from line 95 (starting with "Now sign \'Gimme flag\' with the private key") up to line 115 (maybe up to the line before "sig_hex = signature.hex()"?). Actually, I want to insert verification test before signing "Gimme flag". Let\'s do a bigger replacement: from line 90 to line 115. Let me read lines 85-125 to be safe. Let\'s use a more precise approach: I\'ll write new code and replace the whole block from after recovery to before verification request.\n\nLet me write the new block:\n\n```python\n # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n\n # Create signing key from recovered private key\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n\n # Test verification with a random message\n test_msg = b"test"\n test_sig = sk.sign(test_msg, k=k) # use same k for consistency\n test_sig_hex = test_sig.hex()\n log.info(f"Testing verification with message \'test\'")\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", test_msg)\n io.sendlineafter(b"Enter signature in hex:", test_sig_hex.encode())\n resp = io.recvline(timeout=1).decode().strip()\n if resp == "Good signature":\n log.success("Verification test passed! Private key is correct.")\n else:\n log.error("Verification test failed. Private key may be wrong.")\n log.error(f"Response: {resp}")\n # Try to read more\n try:\n extra = io.recv(timeout=0.5).decode()\n log.error(f"Extra: {extra}")\n except:\n pass\n io.close()\n return None\n\n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # Use deterministic signing (no k specified) - should work\n signature = sk.sign(target_msg) # default random k\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")\n```\n\nBut we need to be careful: after sending verification test, we need to wait for the prompt again? The server prints "Good signature" and then loops back to waiting for action. So we need to read the line "Good signature" and then we can continue. The server will then print "Input action (1 for sign, 2 for verify):". However, our `io.sendlineafter` expects that prompt. But after verification, the server prints "Good signature" and then prints the prompt again. We need to read the "Good signature" line first, then wait for the prompt. Actually, we used `io.recvline` to read "Good signature". That\'s fine. After that, the server will send the prompt. So we need to wait for that prompt before sending the next action. We\'ll use `io.recvuntil("Input action")`? Let\'s just use `io.sendlineafter` again, which will wait for the prompt. Since we already read the "Good signature" line, the next line is the prompt. However, there might be a newline after "Good signature". The server prints with `print("Good signature")` which includes newline. So we need to consume that newline. `recvline` already consumes the newline. Good.\n\nThus after reading "Good signature", we can use `io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")` again. That will wait for the prompt to appear. However, the prompt may have already been sent before we call `sendlineafter`. The socket buffer may already contain the prompt. `sendlineafter` will read from socket until it sees the prompt, then send our line. That\'s fine.\n\nLet\'s implement.\n\nNow, we also need to ensure we don\'t close connection prematurely. Let\'s edit. Let me find the exact old_string to replace. I\'ll replace from line 85 to line 115 (up to the line before "sig_hex = signature.hex()"). Let me get the exact text. Let\'s copy lines 85-115 into a variable. Let me read them. Let\'s do a quick manual: I\'ll write the new block and replace. Let me do edit now.', 'thought': True}, {'functionCall': {'id': 'call_00_izT68Vq5WIFw3G5LeZQjcEzN', 'name': 'edit', 'args': {'file_path': '/home/jiegec/ctf/temp/exploit.py', 'old_string': ' # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n\n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # We need to produce a signature using the same k? Actually we can sign with any k.\n # But we can use the recovered private key to sign properly.\n # Create a signing key object from d\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n # Sign the target message with a random k (or we can reuse k if we want)\n # Use deterministic ECDSA (default) or we can specify k.\n signature = sk.sign(target_msg, k=k) # use same k for simplicity\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")', 'new_string': ' # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n\n # Create signing key from recovered private key\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n\n # Test verification with a random message\n test_msg = b"test"\n test_sig = sk.sign(test_msg, k=k) # use same k for consistency\n test_sig_hex = test_sig.hex()\n log.info(f"Testing verification with message \'test\'")\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", test_msg)\n io.sendlineafter(b"Enter signature in hex:", test_sig_hex.encode())\n resp = io.recvline(timeout=1).decode().strip()\n if resp == "Good signature":\n log.success("Verification test passed! Private key is correct.")\n else:\n log.error("Verification test failed. Private key may be wrong.")\n log.error(f"Response: {resp}")\n # Try to read more\n try:\n extra = io.recv(timeout=0.5).decode()\n log.error(f"Extra: {extra}")\n except:\n pass\n io.close()\n return None\n\n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # Use deterministic signing (no k specified) - should work\n signature = sk.sign(target_msg) # default random k\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")'}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_izT68Vq5WIFw3G5LeZQjcEzN', 'name': 'edit', 'response': {'output': 'The file: /home/jiegec/ctf/temp/exploit.py has been updated. Showing lines 88-126 of 176 from the edited file:\n\n---\n\n # Recover private key\n d, k = recover_private_key(r, s1, s2, h1, h2)\n log.success(f"Recovered private key: {hex(d)}")\n log.success(f"Recovered nonce k: {hex(k)}")\n\n # Create signing key from recovered private key\n sk = SigningKey.from_secret_exponent(d, curve=NIST256p)\n\n # Test verification with a random message\n test_msg = b"test"\n test_sig = sk.sign(test_msg, k=k) # use same k for consistency\n test_sig_hex = test_sig.hex()\n log.info(f"Testing verification with message \'test\'")\n io.sendlineafter(b"Input action (1 for sign, 2 for verify):", b"2")\n io.sendlineafter(b"Enter message:", test_msg)\n io.sendlineafter(b"Enter signature in hex:", test_sig_hex.encode())\n resp = io.recvline(timeout=1).decode().strip()\n if resp == "Good signature":\n log.success("Verification test passed! Private key is correct.")\n else:\n log.error("Verification test failed. Private key may be wrong.")\n log.error(f"Response: {resp}")\n # Try to read more\n try:\n extra = io.recv(timeout=0.5).decode()\n log.error(f"Extra: {extra}")\n except:\n pass\n io.close()\n return None\n\n # Now sign "Gimme flag" with the private key\n target_msg = b"Gimme flag"\n # Use deterministic signing (no k specified) - should work\n signature = sk.sign(target_msg) # default random k\n sig_hex = signature.hex()\n log.success(f"Forged signature for \'Gimme flag\': {sig_hex}")\n \n # Send verify request'}}}]}
{'role': 'model', 'parts': [{'text': 'Now we need to adjust the remaining code: after signing "Gimme flag", we need to send verification request. The previous verification request lines are still there (lines after). Let\'s check that we have the correct "Send verify request" section. It\'s still present after the new block. But we need to ensure we wait for the prompt after the test verification. Actually, after receiving "Good signature", the server will print the prompt again. However, we haven\'t consumed that prompt. The `io.recvline` reads only the "Good signature" line, but the prompt is still in the buffer? Actually, the server prints "Good signature\\n" and then prints "Input action (1 for sign, 2 for verify):". That second line is sent immediately after the first. The socket may have both lines already. `recvline` reads until newline, leaving the prompt line in the buffer. Then our next `io.sendlineafter` will try to wait for the prompt, but it\'s already in the buffer, so it will match immediately and send our line. That\'s fine.\n\nBut we need to be careful: after the test verification, we should not call `io.sendlineafter` again because we still have the prompt pending. Actually, we want to send another action (2) for the "Gimme flag" verification. We need to wait for the prompt again. Since the prompt is already in buffer, we can use `io.sendlineafter(b"Input action", b"2")` which will read the prompt from buffer and send our line. That\'s fine.\n\nThus we keep the existing verification request lines. Let\'s verify they are still there. Let\'s read from line 130 onward. Let\'s do a quick read. Let\'s run the updated exploit now. First, mark todo 3 as completed and move to todo 4.', 'thought': True}, {'functionCall': {'id': 'call_00_xDUlQBRTxWtUiW2CAy5SYZSw', 'name': 'todo_write', 'args': {'todos': [{'id': '1', 'content': 'Examine main.py and understand the vulnerability', 'status': 'completed'}, {'id': '2', 'content': 'Write exploit script to connect to remote service', 'status': 'completed'}, {'id': '3', 'content': 'Collect two signatures with same k', 'status': 'completed'}, {'id': '4', 'content': 'Compute private key using nonce reuse', 'status': 'in_progress'}, {'id': '5', 'content': "Sign 'Gimme flag' message", 'status': 'pending'}, {'id': '6', 'content': 'Verify and get flag', 'status': 'pending'}]}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_xDUlQBRTxWtUiW2CAy5SYZSw', 'name': 'todo_write', 'response': {'output': 'Todos have been modified successfully. Ensure that you continue to use the todo list to track your progress. Please proceed with the current tasks if applicable\n\n<system-reminder>\nYour todo list has changed. DO NOT mention this explicitly to the user. Here are the latest contents of your todo list: \n\n[{"id":"1","content":"Examine main.py and understand the vulnerability","status":"completed"},{"id":"2","content":"Write exploit script to connect to remote service","status":"completed"},{"id":"3","content":"Collect two signatures with same k","status":"completed"},{"id":"4","content":"Compute private key using nonce reuse","status":"in_progress"},{"id":"5","content":"Sign \'Gimme flag\' message","status":"pending"},{"id":"6","content":"Verify and get flag","status":"pending"}]. Continue on with the tasks at hand if applicable.\n</system-reminder>'}}}]}
{'role': 'model', 'parts': [{'text': 'Now run the exploit.', 'thought': True}, {'functionCall': {'id': 'call_00_bqzLMgHggPzE7jHUIRzbrgUk', 'name': 'run_shell_command', 'args': {'command': 'cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1', 'is_background': False}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_bqzLMgHggPzE7jHUIRzbrgUk', 'name': 'run_shell_command', 'response': {'output': "Command: cd /home/jiegec/ctf/temp && python3 exploit.py 2>&1\nDirectory: (root)\nOutput: [*] Starting local test...\n[*] Local test skipped; proceeding to remote.\n[*] Connecting to ctf.jia.je:32789\n[x] Opening connection to ctf.jia.je on port 32789\n[x] Opening connection to ctf.jia.je on port 32789: Trying 172.238.22.117\n[+] Opening connection to ctf.jia.je on port 32789: Done\n[+] Got signature 1: 2cfa0f7100befda6c8b6a9d290a1df38061740d8a4559f47dabaf8bf0152da9d8990f63af87cecd14a0f3770c874e7efd8f06a235af9fb642abcbb73a1311c6d\n[+] Got signature 2: 2cfa0f7100befda6c8b6a9d290a1df38061740d8a4559f47dabaf8bf0152da9d6acc3622173de7fa6e9066429fc84ddbde7f3a9bb1b00e8f6af54b11512f64c7\n[+] Recovered private key: 0xf8705bb2e4fc739f9f912c75deacc1a006816a6e99b02a0ada4dea64d0bd355b\n[+] Recovered nonce k: 0x54ae103dd6d3994b45eda988f717f22ccbbbb00b1a7c6f5410e131253cc25ba4\n[*] Testing verification with message 'test'\n[+] Verification test passed! Private key is correct.\n[+] Forged signature for 'Gimme flag': bc6056dee5a2991627faa404f3139c97edfb457c5752a00320aeeece645220423665ae1fae498f86cc3757aba687550798b6cc2b7ab84f4442920181c26d0428\n[*] Line1: Good signature\n[*] Line2: Give you the flag\n[+] Flag: flag{never_reuse_ecdsa_nonce}\n[*] Closed connection to ctf.jia.je port 32789\nflag{never_reuse_ecdsa_nonce}\nError: (none)\nExit Code: 0\nSignal: (none)\nBackground PIDs: 2048421\nProcess Group PGID: (none)"}}}]}
{'role': 'model', 'parts': [{'text': "Great! The exploit succeeded and we got the flag. Let's mark the remaining todos as completed. Now we have solved the CTF challenge. Let's output the flag to the user. First, finalize todos.", 'thought': True}, {'functionCall': {'id': 'call_00_qI9gojaVszcwtEzNL9z8hjOp', 'name': 'todo_write', 'args': {'todos': [{'id': '1', 'content': 'Examine main.py and understand the vulnerability', 'status': 'completed'}, {'id': '2', 'content': 'Write exploit script to connect to remote service', 'status': 'completed'}, {'id': '3', 'content': 'Collect two signatures with same k', 'status': 'completed'}, {'id': '4', 'content': 'Compute private key using nonce reuse', 'status': 'completed'}, {'id': '5', 'content': "Sign 'Gimme flag' message", 'status': 'completed'}, {'id': '6', 'content': 'Verify and get flag', 'status': 'completed'}]}}}]}
{'role': 'user', 'parts': [{'functionResponse': {'id': 'call_00_qI9gojaVszcwtEzNL9z8hjOp', 'name': 'todo_write', 'response': {'output': 'Todos have been modified successfully. Ensure that you continue to use the todo list to track your progress. Please proceed with the current tasks if applicable\n\n<system-reminder>\nYour todo list has changed. DO NOT mention this explicitly to the user. Here are the latest contents of your todo list: \n\n[{"id":"1","content":"Examine main.py and understand the vulnerability","status":"completed"},{"id":"2","content":"Write exploit script to connect to remote service","status":"completed"},{"id":"3","content":"Collect two signatures with same k","status":"completed"},{"id":"4","content":"Compute private key using nonce reuse","status":"completed"},{"id":"5","content":"Sign \'Gimme flag\' message","status":"completed"},{"id":"6","content":"Verify and get flag","status":"completed"}]. Continue on with the tasks at hand if applicable.\n</system-reminder>'}}}]}
{'role': 'model', 'parts': [{'text': "Now we can present the flag. Let's also clean up if needed. The exploit script is fine. Let's output the flag.", 'thought': True}, {'text': 'flag{never_reuse_ecdsa_nonce}'}]}
╭───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ │
│ Agent powering down. Goodbye! │
│ │
│ Interaction Summary │
│ Session ID: 5c4c0a93-a485-4f29-a1fd-7aa2a4b5f817 │
│ Tool Calls: 18 ( ✓ 18 x 0 ) │
│ Success Rate: 100.0% │
│ Code Changes: +188 -12 │
│ │
│ Performance │
│ Wall Time: 6m 52s │
│ Agent Active: 5m 53s │
│ » API Time: 5m 34s (94.7%) │
│ » Tool Time: 18.8s (5.3%) │
│ │
│ │
│ Model Usage Reqs Input Tokens Output Tokens │
│ ─────────────────────────────────────────────────────────────── │
│ deepseek-reasoner 20 343,525 9,582 │
│ │
│ Savings Highlight: 324,544 (94.5%) of input tokens were served from the cache, reducing costs. │
│ │
│ » Tip: For a full token breakdown, run `/stats model`. │
│ │
╰───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯