http://hg.viff.dk/viff/rev/e530dfcb40cd
changeset: 1083:e530dfcb40cd
user: Marcel Keller <[email protected]>
date: Thu Jan 15 18:30:46 2009 +0100
summary: Implemented inversion by exponentiation in AES ByteSub.
diffstat:
2 files changed, 63 insertions(+), 34 deletions(-)
viff/aes.py | 81 ++++++++++++++++++++++++++++++-------------------
viff/test/test_aes.py | 16 +++++++--
diffs (148 lines):
diff -r c1b3ced5bf05 -r e530dfcb40cd viff/aes.py
--- a/viff/aes.py Wed Jan 14 18:33:33 2009 +0100
+++ b/viff/aes.py Thu Jan 15 18:30:46 2009 +0100
@@ -51,7 +51,8 @@
class AES:
- def __init__(self, runtime, key_size, block_size=128):
+ def __init__(self, runtime, key_size, block_size=128,
+ use_exponentiation=False):
"""Initialize Rijndael.
AES(runtime, key_size, block_size), whereas key size and block
@@ -66,6 +67,7 @@
self.n_b = block_size / 32
self.rounds = max(self.n_k, self.n_b) + 6
self.runtime = runtime
+ self.use_exponentiation = use_exponentiation
# matrix for byte_sub
A = Matrix([[1,0,0,0,1,1,1,1],
@@ -83,39 +85,58 @@
The first argument should be a matrix consisting of elements
of GF(2^8)."""
+ def invert_by_masking(byte):
+ bits = bit_decompose(byte)
+
+ for j in range(len(bits)):
+ bits[j] = 1 - bits[j]
+
+ while(len(bits) > 1):
+ bits.append(bits.pop() * bits.pop())
+
+ # b == 1 if byte is 0, b == 0 else
+ b = bits[0]
+
+ r = Share(self.runtime, GF256)
+ c = Share(self.runtime, GF256)
+
+ def get_masked_byte(c_opened, r_related, c, r, byte):
+ if (c_opened == 0):
+ r_trial = self.runtime.prss_share_random(GF256)
+ c_trial = self.runtime.open((byte + b) * r_trial)
+ c_trial.addCallback(get_masked_byte, r_trial,
+ c, r, byte)
+ else:
+ r_related.addCallback(r.callback)
+ c.callback(~c_opened)
+
+ get_masked_byte(0, None, c, r, byte)
+ return c * r - b
+
+ def invert_by_exponentiation(byte):
+ byte_2 = byte * byte
+ byte_3 = byte_2 * byte
+ byte_6 = byte_3 * byte_3
+ byte_12 = byte_6 * byte_6
+ byte_15 = byte_12 * byte_3
+ byte_30 = byte_15 * byte_15
+ byte_60 = byte_30 * byte_30
+ byte_63 = byte_60 * byte_3
+ byte_126 = byte_63 * byte_63
+ byte_252 = byte_126 * byte_126
+ byte_254 = byte_252 * byte_2
+ return byte_254
+
+ if (self.use_exponentiation):
+ invert = invert_by_exponentiation
+ else:
+ invert = invert_by_masking
+
for h in range(len(state)):
row = state[h]
for i in range(len(row)):
- byte = row[i]
- bits = bit_decompose(byte)
-
- for j in range(len(bits)):
- bits[j] = 1 - bits[j]
-
- while(len(bits) > 1):
- bits.append(bits.pop() * bits.pop())
-
- # b == 1 if byte is 0, b == 0 else
- b = bits[0]
-
- r = Share(self.runtime, GF256)
- c = Share(self.runtime, GF256)
-
- def get_masked_byte(c_opened, r_related, c, r, byte):
- if (c_opened == 0):
- r_trial = self.runtime.prss_share_random(GF256)
- c_trial = self.runtime.open((byte + b) * r_trial)
- c_trial.addCallback(get_masked_byte, r_trial,
- c, r, byte)
- else:
- r_related.addCallback(r.callback)
- c.callback(~c_opened)
-
- get_masked_byte(0, None, c, r, byte)
- inverted_byte = c * r - b
-
- bits = bit_decompose(inverted_byte)
+ bits = bit_decompose(invert(row[i]))
# caution: order is lsb first
vector = AES.A * Matrix(zip(bits)) +
Matrix(zip([1,1,0,0,0,1,1,0]))
diff -r c1b3ced5bf05 -r e530dfcb40cd viff/test/test_aes.py
--- a/viff/test/test_aes.py Wed Jan 14 18:33:33 2009 +0100
+++ b/viff/test/test_aes.py Thu Jan 15 18:30:46 2009 +0100
@@ -69,9 +69,7 @@
return gather_shares(opened_results)
- @protocol
- def test_byte_sub(self, runtime):
- aes = AES(runtime, 128)
+ def _test_byte_sub(self, runtime, aes):
results = []
expected_results = []
@@ -81,13 +79,23 @@
for j in range(4):
b = 60 * i + j
- results[i].append(Share(runtime, GF256, b))
+ results[i].append(Share(runtime, GF256, GF256(b)))
expected_results[i].append(S[b])
aes.byte_sub(results)
self.verify(runtime, results, expected_results)
@protocol
+ def test_byte_sub_with_masking(self, runtime):
+ self._test_byte_sub(runtime, AES(runtime, 128,
+ use_exponentiation=False))
+
+ @protocol
+ def test_byte_sub_with_exponentiation(self, runtime):
+ self._test_byte_sub(runtime, AES(runtime, 128,
+ use_exponentiation=True))
+
+ @protocol
def test_key_expansion(self, runtime):
aes = AES(runtime, 256)
key = []
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