On Friday, October 18, 2013 4:53:31 PM UTC-4, Piotr Bratkowski wrote:
>
> Hello,
>
> I'm writing my Master of Science work, that is group EC DH chat program. I 
> have everything working with basic version, but now I'm creating version 
> that is using point compression
>
> I'm sending base64 encoded points to my clients. At arrival I'm parsing 
> data, decoding and then using point compression to get my data. 
>
> I have problem because I see that every client is getting same base64 
> encoded vector of data and after decoding data is the same, but after point 
> decompression I sometimes have null values. 
> ...
>
> I was also tring do decode like this:
>
> StringSource ssECPoint(sECPoint, true, new Base64Decoder);
>> curve.DecodePoint(ecPoint, ssECPoint,(size_t)ssECPoint.MaxRetrievable());
>>
>
> But then I get nulls insted of different values.
>
> What is interesting is that this behavior is totaly random, sometimes it 
> works totally fine and sometimes I get this strange results. 
>
> Do any of you have idea what could be wrong? I even tried to replace 
> base64 encoding with hex encoding, so in my opinion problem is with point 
> decompression, but I have no idea where to look for a solution.
>
Have you had a look at Wei's suggestion at 
http://www.cryptopp.com/wiki/Elliptic_Curve_Cryptography#Minimizing_Key_Size_for_Persistence?

Also see 
http://stackoverflow.com/questions/16576434/cryptopp-compressed-ec-keys.

Jeff 

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