# Re: [viff-devel] Equality protocol : error

```Dear Ivan,

Yes I know about that. But 367 is 3 mod 4 so it should be OK. And the existing
protocol works with 367 only if the two numbers are not equal. If they are, I
got the error mentioned in my first message.
If I can solve the error in the existing protocol, I will be able to continue
my work.```
```

Jonathan

Le 8 avr. 2010 à 16:26, Ivan Damgård a écrit :

> Dear Jonathan,
>
> You cannot expect the protocol to work for primes that are 1 mod 4,
> it is based on the fact that for primes p that are 3 mod 4, you can
> deterministically
> compute a square root mod p by raising to power (p+1)/4.
> This does not work if p is 1 mod 4.
>
> regards, Ivan
>
> On 08/04/2010, at 14.11, Jonathan Van den Schrieck wrote:
>
>> Hello,
>>
>> I am trying to modify the equality protocol to make it work for primes
>> congruent to 5 mod 8 (exists for Blum primes).
>> The problem is that I have an error with the original protocol. It works
>> perfectly with p = 211 for example. But for p = 367, it doesn't.
>> Here is the code I'm using to test it :
>>
>> from optparse import OptionParser
>> import viff.reactor
>> viff.reactor.install()
>> from twisted.internet import reactor
>> from viff.field import GF
>> from viff.runtime import create_runtime, gather_shares
>> from viff.passive import PassiveRuntime
>> from viff.equality_ohta import ProbabilisticEqualityMixin2
>> from viff.equality import ProbabilisticEqualityMixin
>> from viff.comparison import Toft05Runtime
>> from viff.util import rand, find_prime
>>
>> class EqualityRuntime(PassiveRuntime, ProbabilisticEqualityMixin):
>>     """Default mix of :class:`~viff.equality.ProbabilisticEqualityMixin`
>>     and :class:`~viff.passive.PassiveRuntime`.
>>     """
>>     pass
>>
>> class Protocol:
>>
>>     def __init__(self, runtime):
>>         # Save the Runtime for later use
>>         self.runtime = runtime
>>         k = runtime.options.security_parameter
>>         print "security parameter = ", k
>>         Zp = GF(367)
>>
>>         # We must secret share our input with the other parties. They
>>         # will do the same and we end up with three variables
>>         # input is equal to the player id
>>
>>         rand1 = rand
>>         print "rand = ", rand, "rand1 = ", rand1
>>
>>         #open rand and rand1 to print their value
>>         open_rand = runtime.open(rand)
>>         open_rand1 = runtime.open(rand1)
>>         temp = gather_shares([open_rand, open_rand1])
>>
>>         # we test if rand == rand1 by using equality protocol
>>         test = (rand == rand1)
>>         test_open = runtime.open(test)
>>         results = gather_shares([test_open])
>>
>>         runtime.schedule_callback(results, lambda _: runtime.synchronize())
>>         runtime.schedule_callback(results, lambda _: runtime.shutdown())
>>
>>         print "ALGO_QUAD temp results =", results
>>
>>
>>     def mtemp(self, temp):
>>          print "local part of shares after callback ="
>>          print temp
>>
>>
>> # Parse command line arguments.
>> parser = OptionParser()
>> options, args = parser.parse_args()
>>
>> if len(args) == 0:
>>     parser.error("you must specify a config file")
>> else:
>>
>> # Create a deferred Runtime and ask it to run our protocol when ready.
>> pre_runtime = create_runtime(id, players, 1, options, EqualityRuntime)
>>
>> # Start the Twisted event loop.
>> reactor.run()
>>
>> as you can see, I simply generate 2 random numbers, then I test if they have
>> the same value, and I print the result of the test.
>> This will work if rand != rand1, but if I set rand1 = rand => ERROR.
>> This error will only happen if p = 367 (and maybe with others primes, but I
>> couldn't test them all)
>> Here is the error :
>>
>> Unhandled error in Deferred:
>> Traceback (most recent call last):
>>   File
>> "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/twisted/internet/defer.py",
>>  line 328, in _runCallbacks
>>     self.result = callback(self.result, *args, **kw)
>>   File "/Users/jonathanvds/opt/lib/python/viff/runtime.py", line 239, in
>> _callback_fired
>>     self.callback(self.results)
>>   File
>> "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/twisted/internet/defer.py",
>>  line 243, in callback
>>     self._startRunCallbacks(result)
>>   File
>> "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/twisted/internet/defer.py",
>>  line 312, in _startRunCallbacks
>>     self._runCallbacks()
>> --- <exception caught here> ---
>>   File
>> "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/twisted/internet/defer.py",
>>  line 328, in _runCallbacks
>>     self.result = callback(self.result, *args, **kw)
>>   File "/Users/jonathanvds/opt/lib/python/viff/passive.py", line 211, in
>> <lambda>
>>     result.addCallback(lambda (a, b): a * b)
>> exceptions.TypeError: unsupported operand type(s) for *: 'instance' and
>> 'GFElement'
>>
>> I can't find where the problem comes from since I only have the error with p
>> = 367 (and I have the same error with my new protocol for p = 5 mod 8, but
>> I'm guessing that if I can solve the problem in the existing protocol, I'll
>> be able to do the same with my implementation).
>>
>> Thank you for your help,
>>
>> Jonathan Van den Schrieck
>>
>>
>> _______________________________________________
>> viff-devel mailing list (http://viff.dk/)
>> viff-devel@viff.dk
>> http://lists.viff.dk/listinfo.cgi/viff-devel-viff.dk
>

```
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