91 行
2.4 KiB
Python
91 行
2.4 KiB
Python
import base64
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import io
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import secrets
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from captcha.image import ImageCaptcha
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from website.constants import BACKGROUND_COLOUR, CONFIG, CAPTCHA_SECRET_KEY
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import werkzeug.security
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import time
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import base64
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import math
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CAPTCHA_CHARSET = '346wertypagkxvbm'
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CAPTCHA_LENGTH = 3
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CAPTCHA = ImageCaptcha(width=72, height=30, fonts=CONFIG['captcha']['fonts'], font_sizes=(24, 27, 30))
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class FakeCiphertext(Exception):
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pass
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class Incorrect(Exception):
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pass
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def _image_to_base64(im):
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buffer = io.BytesIO()
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im.save(buffer, format='jpeg', quality=70)
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buffer.seek(0)
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b64 = base64.b64encode(buffer.read()).rstrip(b'=')
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return (b'data:image/jpeg;base64,' + b64).decode()
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def xor_bytes(data1, data2):
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return bytes(byte1 ^ byte2 for byte1, byte2 in zip(data1, data2))
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def pbkdf2(salt, text):
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data = werkzeug.security._hash_internal('pbkdf2:sha256', salt, text)[0]
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data = bytes.fromhex(data)
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return data
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def gen_captcha():
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answer = ''.join(secrets.choice(CAPTCHA_CHARSET) for _ in range(CAPTCHA_LENGTH))
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im = CAPTCHA.create_captcha_image(answer, (0xff, 0xff, 0xff), tuple(BACKGROUND_COLOUR))
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# current time in bytes
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now = int(time.time())
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n_bits = now.bit_length() + -now.bit_length() % 8
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now = f'{now:0{n_bits // 4}x}'
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now = bytes.fromhex(now)
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# create plaintext
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plaintext = b'\0' * 4 + now
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# create xor key
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key = pbkdf2(CAPTCHA_SECRET_KEY, answer)
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# create middletext
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middletext = xor_bytes(plaintext, key)
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# create ciphertext
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outer_key = pbkdf2(CAPTCHA_SECRET_KEY, middletext.hex())
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ciphertext = outer_key[:4] + middletext
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return _image_to_base64(im), base64.b64encode(ciphertext).decode()
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def get_creation_time(ciphertext, answer):
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# get ciphertext
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try:
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ciphertext = base64.b64decode(ciphertext)
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except:
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raise FakeCiphertext
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# create middletext
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determinant = ciphertext[:4]
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middletext = ciphertext[4:]
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outer_key = pbkdf2(CAPTCHA_SECRET_KEY, middletext.hex())
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if outer_key[:4] != determinant:
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raise FakeCiphertext
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# create xor key
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key = pbkdf2(CAPTCHA_SECRET_KEY, answer)
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# create plaintext
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plaintext = xor_bytes(middletext, key)
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determinant = int.from_bytes(plaintext[:4], 'big')
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timestamp = int.from_bytes(plaintext[4:], 'big')
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# captcha answer was incorrect
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if determinant != 0:
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raise Incorrect(timestamp)
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return timestamp
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