captcha.py

import Crypto.Cipher.AES as aes
import base64
import random
from StringIO import StringIO

from PIL import Image, ImageFont, ImageDraw


def generate_id():
    from common.conf import settings
    imgtext = ''.join([str(random.randint(10, 90)) + '+' + str(random.randint(0, 9)) + '='])

    # encrypt it
    iv = ''.join([chr(random.randint(0, 255)) for i in range(16)])
    a = aes.new(settings.CAPTCHAKEY, mode=aes.MODE_CBC, IV=iv)
    pad_val = aes.block_size - (len(imgtext) % aes.block_size)
    imgtext += chr(pad_val) * pad_val
    crypttext = a.encrypt(imgtext)

    # Return encoded ID safe for URLs
    return base64.b16encode(iv) + base64.b16encode(crypttext)


def decrypt(captcha_id):
    from common.conf import settings
    iv = base64.b16decode(captcha_id[0:32])
    crypttext = base64.b16decode(captcha_id[32:])
    a = aes.new(settings.CAPTCHAKEY, mode=aes.MODE_CBC, IV=iv)
    imgtext = a.decrypt(crypttext)
    return imgtext[:5]


def generate_image(id):
    from common.conf import settings
    # decrypt captcha id
    imgtxt = str(decrypt(id)).strip()

    # render captcha image
    font = ImageFont.truetype(font=settings.CAPTCHA_FONT, size=16)
    sw, sh = font.getsize(imgtxt)
    im = Image.new('RGBA', (sw, sh + 1), (255, 255, 255, 0))
    d = ImageDraw.Draw(im)
    d.text(xy=(0, -5), text=imgtxt, font=font, fill='black')

    # return image data
    buf = StringIO()
    im.save(buf, 'PNG')
    return buf.getvalue()


def check(usertext, captcha_id):
    return usertext == str(sum(map(int, decrypt(captcha_id).strip('=').split('+'))))