[tor-commits] [bridgedb/master] Change gimp CAPTCHA encoding strategy to assume HMAC is 20 bytes.
isis at torproject.org
isis at torproject.org
Sat Apr 19 17:02:42 UTC 2014
commit 72c1dcc0fa6cc0a2914e8028193879cc06adb2b0
Author: Isis Lovecruft <isis at torproject.org>
Date: Tue Apr 8 14:16:42 2014 +0000
Change gimp CAPTCHA encoding strategy to assume HMAC is 20 bytes.
* CHANGE relevant unittests which looked for the original ';' string
delimiter to now split challenge string, taking the first 20 bytes as
the HMAC, and the rest as the encrypted blob containing the HMAC
answer.
* CHANGE `bridgedb.captcha.GimpCaptcha.check()` to always immediately
return False whenever any Exception occurs.
* ADD eight new unittests for `captcha.GimpCaptcha.check()`.
---
lib/bridgedb/captcha.py | 12 +++--
lib/bridgedb/test/test_captcha.py | 94 +++++++++++++++++++++++++++++++++++--
2 files changed, 97 insertions(+), 9 deletions(-)
diff --git a/lib/bridgedb/captcha.py b/lib/bridgedb/captcha.py
index 6bc3661..6ca7629 100644
--- a/lib/bridgedb/captcha.py
+++ b/lib/bridgedb/captcha.py
@@ -195,11 +195,12 @@ class GimpCaptcha(Captcha):
% (solution, challenge))
try:
decoded = urlsafe_b64decode(challenge)
- hmac, original = decoded.split(';', 1)
+ hmac = decoded[:20]
+ original = decoded[20:]
verified = crypto.getHMAC(hmacKey, original)
validHMAC = verified == hmac
- except Exception as error:
- logging.exception(error)
+ except Exception:
+ return False
finally:
if validHMAC:
decrypted = secretKey.decrypt(original)
@@ -217,7 +218,8 @@ class GimpCaptcha(Captcha):
HMAC ";" ENCRYPTED_ANSWER
- and lastly base64-encoded (in a URL safe manner).
+ where the HMAC MUST be the first 20 bytes. Lastly base64-encoded (in a
+ URL safe manner).
:param str answer: The answer to a CAPTCHA.
:rtype: str
@@ -226,7 +228,7 @@ class GimpCaptcha(Captcha):
"""
encrypted = self.publicKey.encrypt(answer)
hmac = crypto.getHMAC(self.hmacKey, encrypted)
- challenge = hmac + ';' + encrypted
+ challenge = hmac + encrypted
encoded = urlsafe_b64encode(challenge)
return encoded
diff --git a/lib/bridgedb/test/test_captcha.py b/lib/bridgedb/test/test_captcha.py
index b2e67b3..9cc5a89 100644
--- a/lib/bridgedb/test/test_captcha.py
+++ b/lib/bridgedb/test/test_captcha.py
@@ -153,7 +153,7 @@ class GimpCaptchaTests(unittest.TestCase):
self.cacheDir)
challenge = c.createChallenge('w00t')
decoded = urlsafe_b64decode(challenge)
- self.assertTrue(decoded.find(';') >= 1)
+ self.assertTrue(decoded)
def test_createChallenge_hmacValid(self):
"""The HMAC in createChallenge() return value should be valid."""
@@ -161,7 +161,8 @@ class GimpCaptchaTests(unittest.TestCase):
self.cacheDir)
challenge = c.createChallenge('ShouldHaveAValidHMAC')
decoded = urlsafe_b64decode(challenge)
- hmac, orig = decoded.split(';', 1)
+ hmac = decoded[:20]
+ orig = decoded[20:]
correctHMAC = crypto.getHMAC(self.hmacKey, orig)
self.assertEquals(hmac, correctHMAC)
@@ -172,7 +173,8 @@ class GimpCaptchaTests(unittest.TestCase):
answer = 'ThisAnswerShouldDecryptToThis'
challenge = c.createChallenge(answer)
decoded = urlsafe_b64decode(challenge)
- hmac, orig = decoded.split(';', 1)
+ hmac = decoded[:20]
+ orig = decoded[20:]
correctHMAC = crypto.getHMAC(self.hmacKey, orig)
self.assertEqual(hmac, correctHMAC)
decrypted = self.sekrit.decrypt(orig)
@@ -232,6 +234,90 @@ class GimpCaptchaTests(unittest.TestCase):
c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
self.cacheDir)
image, challenge = c.get()
+ challengeBadB64 = challenge.rstrip('==') + "\x42\x42\x42"
self.assertEquals(
- c.check(challenge.rstrip('=='), c.answer, c.secretKey, c.hmacKey),
+ c.check(challenge, c.answer, c.secretKey, c.hmacKey),
+ True)
+ self.assertEquals(
+ c.check(challengeBadB64, c.answer, c.secretKey, c.hmacKey),
+ False)
+
+ def test_check_caseInsensitive_lowercase(self):
+ """A correct answer in lowercase characters should return True."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ solution = c.answer.lower()
+ self.assertEquals(
+ c.check(challenge, solution, c.secretKey, c.hmacKey),
+ True)
+
+ def test_check_caseInsensitive_uppercase(self):
+ """A correct answer in uppercase characters should return True."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ solution = c.answer.upper()
+ self.assertEquals(
+ c.check(challenge, solution, c.secretKey, c.hmacKey),
+ True)
+
+ def test_check_encoding_utf8(self):
+ """A correct answer in utf-8 lowercase should return True."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ solution = c.answer.encode('utf8')
+ self.assertEquals(
+ c.check(challenge, solution, c.secretKey, c.hmacKey),
+ True)
+
+ def test_check_encoding_ascii(self):
+ """A correct answer in utf-8 lowercase should return True."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ solution = c.answer.encode('ascii')
+ self.assertEquals(
+ c.check(challenge, solution, c.secretKey, c.hmacKey),
+ True)
+
+ def test_check_encoding_unicode(self):
+ """A correct answer in utf-8 lowercase should return True."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ solution = unicode(c.answer)
+ self.assertEquals(
+ c.check(challenge, solution, c.secretKey, c.hmacKey),
+ True)
+
+ def test_check_missingHMACbytes(self):
+ """A challenge that is missing part of the HMAC should return False."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ challengeBadHMAC = challenge[:10] + challenge[20:]
+ self.assertEquals(
+ c.check(challengeBadHMAC, c.answer, c.secretKey, c.hmacKey),
+ False)
+
+ def test_check_missingAnswerbytes(self):
+ """Partial encrypted answers in challenges should return False."""
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ challengeBadOrig = challenge[:20] + challenge[30:]
+ self.assertEquals(
+ c.check(challengeBadOrig, c.answer, c.secretKey, c.hmacKey),
+ False)
+
+ def test_check_badHMACkey(self):
+ """A challenge with a bad HMAC key should return False."""
+ hmacKeyBad = crypto.getKey('test_gimpCaptcha_badHMACkey')
+ c = captcha.GimpCaptcha(self.sekrit, self.publik, self.hmacKey,
+ self.cacheDir)
+ image, challenge = c.get()
+ self.assertEquals(
+ c.check(challenge, c.answer, c.secretKey, hmacKeyBad),
False)
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