Index: twisted/test/test_digestauth.py
===================================================================
--- twisted/test/test_digestauth.py	(revision 33585)
+++ twisted/test/test_digestauth.py	(working copy)
@@ -26,20 +26,13 @@
     def __init__(self, *args, **kwargs):
         super(FakeDigestCredentialFactory, self).__init__(*args, **kwargs)
         self.privateKey = "0"
+        self.fakeTime = 0
 
-
-    def _generateNonce(self):
-        """
-        Generate a static nonce
-        """
-        return '178288758716122392881254770685'
-
-
     def _getTime(self):
         """
         Return a stable time
         """
-        return 0
+        return self.fakeTime
 
 
 
@@ -355,38 +348,6 @@
         self.assertFalse(creds.checkPassword(self.password + 'wrong'))
 
 
-    def test_multiResponse(self):
-        """
-        L{DigestCredentialFactory.decode} handles multiple responses to a
-        single challenge.
-        """
-        challenge = self.credentialFactory.getChallenge(self.clientAddress.host)
-
-        nc = "00000001"
-        clientResponse = self.formatResponse(
-            nonce=challenge['nonce'],
-            response=self.getDigestResponse(challenge, nc),
-            nc=nc,
-            opaque=challenge['opaque'])
-
-        creds = self.credentialFactory.decode(clientResponse, self.method,
-                                              self.clientAddress.host)
-        self.assertTrue(creds.checkPassword(self.password))
-        self.assertFalse(creds.checkPassword(self.password + 'wrong'))
-
-        nc = "00000002"
-        clientResponse = self.formatResponse(
-            nonce=challenge['nonce'],
-            response=self.getDigestResponse(challenge, nc),
-            nc=nc,
-            opaque=challenge['opaque'])
-
-        creds = self.credentialFactory.decode(clientResponse, self.method,
-                                              self.clientAddress.host)
-        self.assertTrue(creds.checkPassword(self.password))
-        self.assertFalse(creds.checkPassword(self.password + 'wrong'))
-
-
     def test_failsWithDifferentMethod(self):
         """
         L{DigestCredentialFactory.decode} returns an L{IUsernameHashedPassword}
@@ -669,3 +630,91 @@
         opaque = self.credentialFactory._generateOpaque(
             "long nonce " * 10, None)
         self.assertNotIn('\n', opaque)
+    
+    
+    def test_reusedNonce(self):
+        """
+        L{DigestCredentialFactory.decode} raises L{LoginFailed} when the given
+        same nonce twice
+        """
+        credentialFactory = FakeDigestCredentialFactory(self.algorithm,
+                                                        self.realm)
+        challenge = credentialFactory.getChallenge(self.clientAddress.host)
+
+        key = '%s,%s,%s' % (challenge['nonce'],
+                            self.clientAddress.host,
+                            '0')
+        digest = md5(key + credentialFactory.privateKey).hexdigest()
+        ekey = b64encode(key)
+
+        nonceOpaque = '%s-%s' % (digest, ekey.strip('\n'))
+        
+        self.assertEqual(credentialFactory._verifyOpaque(
+                nonceOpaque,
+                challenge['nonce'],
+                self.clientAddress.host),
+            True)
+
+        self.assertRaises(
+            LoginFailed,
+            credentialFactory._verifyOpaque,
+            nonceOpaque,
+            challenge['nonce'],
+            self.clientAddress.host)
+    
+    
+    def test_nonceTimeoutCleanup(self):
+        """
+        L{DigestCredentialFactory.decode} raises L{LoginFailed} when the given
+        same nonce twice
+        """
+        credentialFactory = FakeDigestCredentialFactory(self.algorithm,
+                                                        self.realm)
+        challenge = credentialFactory.getChallenge(self.clientAddress.host)
+
+        key = '%s,%s,%s' % (challenge['nonce'],
+                            self.clientAddress.host,
+                            str(credentialFactory.fakeTime))
+        digest = md5(key + credentialFactory.privateKey).hexdigest()
+        ekey = b64encode(key)
+
+        nonceOpaque = '%s-%s' % (digest, ekey.strip('\n'))
+        
+        self.assertEqual(credentialFactory._verifyOpaque(
+                nonceOpaque,
+                challenge['nonce'],
+                self.clientAddress.host),
+            True)
+
+        credentialFactory.fakeTime = 10000
+        timeoutChallenge = credentialFactory.getChallenge(self.clientAddress.host)
+        key = '%s,%s,%s' % (timeoutChallenge['nonce'],
+                            self.clientAddress.host,
+                            str(credentialFactory.fakeTime))
+        digest = md5(key + credentialFactory.privateKey).hexdigest()
+        ekey = b64encode(key)
+
+        nonceOpaque = '%s-%s' % (digest, ekey.strip('\n'))
+        
+        self.assertEqual(credentialFactory._verifyOpaque(
+                nonceOpaque,
+                timeoutChallenge['nonce'],
+                self.clientAddress.host),
+            True)
+        
+        # setting the clock back, using the forwarded time earlier as the
+        # "cleanup mechanism"
+        credentialFactory.fakeTime = 0
+        key = '%s,%s,%s' % (challenge['nonce'],
+                            self.clientAddress.host,
+                            str(credentialFactory.fakeTime))
+        digest = md5(key + credentialFactory.privateKey).hexdigest()
+        ekey = b64encode(key)
+
+        nonceOpaque = '%s-%s' % (digest, ekey.strip('\n'))
+        
+        self.assertEqual(credentialFactory._verifyOpaque(
+                nonceOpaque,
+                challenge['nonce'],
+                self.clientAddress.host),
+            True)
\ No newline at end of file
Index: twisted/cred/credentials.py
===================================================================
--- twisted/cred/credentials.py	(revision 33585)
+++ twisted/cred/credentials.py	(working copy)
@@ -7,6 +7,7 @@
 from zope.interface import implements, Interface
 
 import hmac, time, random
+from collections import deque
 from twisted.python.hashlib import md5
 from twisted.python.randbytes import secureRandom
 from twisted.cred._digest import calcResponse, calcHA1, calcHA2
@@ -197,6 +198,8 @@
         self.algorithm = algorithm
         self.authenticationRealm = authenticationRealm
         self.privateKey = secureRandom(12)
+        self.nonces = set()
+        self.nonceTimestamps = deque()
 
 
     def getChallenge(self, address):
@@ -226,7 +229,15 @@
 
         @rtype: C{str}
         """
-        return secureRandom(12).encode('hex')
+        
+        # clean up old nonces
+        while self.nonceTimestamps and int(self._getTime()) - self.nonceTimestamps[0][1] > self.CHALLENGE_LIFETIME_SECS:
+            nonce, age = self.nonceTimestamps.popleft()
+            self.nonces.remove(nonce)
+        
+        # keep track of nonce age
+        nonce = secureRandom(12).encode('hex')
+        return nonce
 
 
     def _getTime(self):
@@ -285,6 +296,10 @@
         if len(keyParts) != 3:
             raise error.LoginFailed('Invalid response, invalid opaque value')
 
+        if nonce in self.nonces:
+            raise error.LoginFailed(
+                'Invalid response, nonce already used')
+        
         if keyParts[0] != nonce:
             raise error.LoginFailed(
                 'Invalid response, incompatible opaque/nonce values')
@@ -310,6 +325,9 @@
         if digest != opaqueParts[0]:
             raise error.LoginFailed('Invalid response, invalid opaque value')
 
+        self.nonces.add(nonce)
+        self.nonceTimestamps.append((nonce, int(self._getTime())))
+
         return True