diff --git a/forwarder.py b/forwarder.py
index 97a7b6b..786e311 100644
--- a/forwarder.py
+++ b/forwarder.py
@@ -26,7 +26,7 @@ def increment_moose(i: num) -> num:
 def test():
     from ethereum.tools import tester2
     c = tester2.Chain()
-    x = c.contract(kode, language='viper')
+    x = c.contract(kode, language='viper', sender=tester2.k3)
     fwdcode = mk_forwarder(x.address)
     initcode = mk_wrapper(fwdcode)
     y = c.contract(initcode, language='evm')
diff --git a/iceage.py b/iceage.py
index 4ae1a8e..931f0ad 100644
--- a/iceage.py
+++ b/iceage.py
@@ -1,12 +1,12 @@
 import random
 import datetime
 
-diffs = [512.60 * 10**12]
-hashpower = diffs[0] / 15.50
-times = [1496227377]
+diffs = [677.20 * 10**12]
+hashpower = diffs[0] / 16.30
+times = [1497319121]
 
 
-for i in range(3797763, 6010000):
+for i in range(3863874, 6010000):
     blocktime = random.expovariate(hashpower / diffs[-1])
     adjfac = max(1 - int(blocktime / 10), -99) / 2048.
     newdiff = diffs[-1] * (1 + adjfac)
diff --git a/utxo_tester.py b/utxo_tester.py
new file mode 100644
index 0000000..f6d1ad6
--- /dev/null
+++ b/utxo_tester.py
@@ -0,0 +1,26 @@
+from ethereum.tools import tester as t
+from ethereum import utils as u
+c = t.Chain()
+x = c.contract(open('utxos.v.py').read(), language='viper', sender=t.k0)
+assert u.normalize_address(x.get_utxos__owner(u.encode_int32(1))) == t.a0
+assert x.get_utxos__value(u.encode_int32(1)) == 2**32
+
+sigdata = u.encode_int32(1) + u.encode_int32(0) + b'\x00' * 12 + t.a2 + \
+    u.encode_int32(2**30) + b'\x00' * 12 + t.a2 + u.encode_int32(3 * 2**30)
+sighash = u.sha3(sigdata)
+
+v, r, s = u.ecsign(sighash, t.k0)
+
+assert x.tx(u.encode_int32(1), u.encode_int32(0), t.a2, 2**30, t.a2, 3 * 2**30, v, r, s) == sighash
+assert u.normalize_address(x.get_utxos__owner(sighash)) == t.a2
+assert x.get_utxos__value(sighash) == 2**30
+
+sigdata2 = sighash + u.encode_int32(0) + b'\x00' * 12 + t.a3 + \
+    u.encode_int32(2**29) + b'\x00' * 12 + t.a3 + u.encode_int32(2**29)
+sighash2 = u.sha3(sigdata2)
+
+v, r, s = u.ecsign(sighash2, t.k2)
+
+assert x.tx(sighash, u.encode_int32(0), t.a3, 2**29, t.a3, 2**29, v, r, s) == sighash2
+
+print('Tests passed')
diff --git a/utxos.v.py b/utxos.v.py
new file mode 100644
index 0000000..828998a
--- /dev/null
+++ b/utxos.v.py
@@ -0,0 +1,19 @@
+utxos: public({owner: address, value: num}[bytes32])
+
+def __init__():
+    self.utxos[as_bytes32(1)] = {owner: msg.sender, value: 4294967296}
+
+def tx(in1: bytes32, in2: bytes32, out1: address, value1: num,
+    out2: address, value2: num, v: num256, r: num256, s: num256) -> bytes32:
+    sighash = sha3(concat(in1, in2, as_bytes32(out1), as_bytes32(value1), as_bytes32(out2), as_bytes32(value2)))
+    sender = ecrecover(sighash, v, r, s)
+    assert self.utxos[in1].owner == sender or not in1
+    assert self.utxos[in2].owner == sender or not in2
+    value = self.utxos[in1].value + self.utxos[in2].value
+    assert value == value1 + value2
+    self.utxos[in1] = {owner: None, value: None}
+    self.utxos[in2] = {owner: None, value: None}
+    self.utxos[sighash] = {owner: out1, value: value1}
+    self.utxos[as_bytes32(bitwise_xor(as_num256(sighash), as_num256(1)))] = \
+        {owner: out2, value: value2}
+    return sighash