diff --git a/eos/core/hashing/__init__.py b/eos/core/hashing/__init__.py
index ef40bb7..4bd0da7 100644
--- a/eos/core/hashing/__init__.py
+++ b/eos/core/hashing/__init__.py
@@ -46,6 +46,8 @@ else:
 # ==============
 
 class SHA256:
+	nbits = 256
+	
 	def __init__(self):
 		if is_python:
 			self.impl = hashlib.sha256()
diff --git a/eos/psr/bitstream.py b/eos/psr/bitstream.py
index 9035062..9641f9f 100644
--- a/eos/psr/bitstream.py
+++ b/eos/psr/bitstream.py
@@ -16,12 +16,13 @@
 
 from eos.core.bigint import *
 from eos.core.objects import *
+from eos.core.hashing import *
 
 class BitStream(EosObject):
-	def __init__(self, value=None):
+	def __init__(self, value=None, nbits=None):
 		if value:
 			self.impl = value
-			self.nbits = self.impl.nbits()
+			self.nbits = nbits if nbits else self.impl.nbits()
 		else:
 			self.impl = ZERO
 			self.nbits = 0
@@ -58,6 +59,17 @@ class BitStream(EosObject):
 		self.ptr += nbits
 		self.nbits += nbits
 	
+	# Append to the end without affecting ptr
+	def append(self, bits, nbits=None):
+		if nbits is None:
+			nbits = bits.nbits()
+		if nbits < bits.nbits():
+			raise Exception('Too many bits to append to BitString')
+		
+		self.impl = (self.impl << nbits) | bits
+		self.nbits += nbits
+		self.remaining += nbits
+	
 	def read_string(self):
 		length = self.read(32)
 		length = length.__int__() # JS attempts to call this twice if we do it in one line
@@ -124,3 +136,23 @@ class BitStream(EosObject):
 	@classmethod
 	def deserialise(cls, value):
 		return cls(value)
+
+class InfiniteHashBitStream(BitStream):
+	def __init__(self, seed):
+		self.sha = SHA256()
+		self.sha.update_bigint(seed)
+		self.ctr = 0
+		self.sha.update_text(str(self.ctr))
+		
+		super().__init__(self.sha.hash_as_bigint(), self.sha.nbits)
+	
+	def read(self, nbits=None):
+		# 11000110110
+		#    ^----
+		if nbits is None:
+			nbits = self.remaining
+		while nbits > self.remaining:
+			self.ctr += 1
+			self.sha.update_text(str(self.ctr))
+			self.append(self.sha.hash_as_bigint(), self.sha.nbits)
+		return super().read(nbits)
diff --git a/eos/psr/election.py b/eos/psr/election.py
index 49a6ce0..b049109 100644
--- a/eos/psr/election.py
+++ b/eos/psr/election.py
@@ -16,6 +16,7 @@
 
 from eos.core.bigint import *
 from eos.core.objects import *
+from eos.core.hashing import *
 from eos.base.election import *
 from eos.psr.bitstream import *
 from eos.psr.crypto import *
@@ -48,15 +49,29 @@ class Trustee(EmbeddedObject):
 	email = StringField()
 
 class MixChallengeResponse(EmbeddedObject):
-	index = IntField()
+	challenge_index = IntField()
+	response_index = IntField()
 	reenc = EmbeddedObjectListField(BigInt)
 	rand = EmbeddedObjectField(BigInt)
 
 class MixingTrustee(Trustee):
 	mixed_questions = ListField(EmbeddedObjectListField(BlockEncryptedAnswer))
 	commitments = ListField(EmbeddedObjectListField(BigInt))
-	challenge = EmbeddedObjectField(BigInt)
+	challenge = EmbeddedObjectListField(BigInt)
 	response = ListField(EmbeddedObjectListField(MixChallengeResponse))
+	
+	def __init__(self, **kwargs):
+		super().__init__(**kwargs)
+		self.mixnets = [] # TODO: Remove this stuff
+	
+	def compute_challenge(self, question_num):
+		sha = SHA256()
+		trustees = self.recurse_parents(Election).mixing_trustees
+		for i in range(len(trustees)):
+			sha.update_text(EosObject.to_json(MixingTrustee._fields['mixed_questions'].element_field.serialise(trustees[i].mixed_questions[question_num])))
+		for i in range(self._instance[1]):
+			sha.update_text(EosObject.to_json(MixingTrustee._fields['response'].element_field.serialise(trustees[i].response[question_num])))
+		return sha
 
 class PSRElection(Election):
 	_db_name = Election._name
diff --git a/eos/psr/tests.py b/eos/psr/tests.py
index 8b14122..80c950b 100644
--- a/eos/psr/tests.py
+++ b/eos/psr/tests.py
@@ -242,7 +242,8 @@ class ElectionTestCase(EosTestCase):
 		# Do the mix
 		for i in range(len(election.questions)):
 			for j in range(len(election.mixing_trustees)):
-				mixnet = RPCMixnet(j)
+				# Wouldn't happen server-side IRL
+				election.mixing_trustees[j].mixnets.append(RPCMixnet(j))
 				if j > 0:
 					orig_answers = election.mixing_trustees[j - 1].mixed_questions[i]
 				else:
@@ -250,7 +251,7 @@ class ElectionTestCase(EosTestCase):
 					for voter in election.voters:
 						for ballot in voter.ballots:
 							orig_answers.append(ballot.encrypted_answers[i])
-				shuffled_answers, commitments = mixnet.shuffle(orig_answers)
+				shuffled_answers, commitments = election.mixing_trustees[j].mixnets[i].shuffle(orig_answers)
 				election.mixing_trustees[j].mixed_questions.append(EosList(shuffled_answers))
 				election.mixing_trustees[j].commitments.append(EosList(commitments))
 		
@@ -261,7 +262,30 @@ class ElectionTestCase(EosTestCase):
 		election.workflow.get_task('eos.psr.workflow.TaskVerifyMixes').enter()
 		election.save()
 		
-		# TODO
+		# Record challenge responses
+		for i in range(len(election.questions)):
+			for j in range(len(election.mixing_trustees)):
+				trustee = election.mixing_trustees[j]
+				if j % 2 == 0:
+					trustee.challenge.append(trustee.compute_challenge(i).hash_as_bigint())
+				else:
+					trustee.challenge.append(election.mixing_trustees[j - 1].challenge[i])
+				challenge_bs = InfiniteHashBitStream(trustee.challenge[i])
+				
+				trustee.response.append(EosList())
+				
+				nbits = BigInt(len(trustee.mixed_questions[i])).nbits()
+				for k in range(len(trustee.mixed_questions[i])):
+					challenge_bit = challenge_bs.read(1)
+					should_reveal = ((j % 2) == (challenge_bit % 2))
+					if should_reveal:
+						response = trustee.mixnets[i].challenge(k)
+						trustee.response[i].append(MixChallengeResponse(
+							challenge_index=k,
+							response_index=response[0],
+							reenc=response[1],
+							rand=response[2]
+						))
 		
 		election.workflow.get_task('eos.psr.workflow.TaskVerifyMixes').exit()
 		election.save()