Created Unassigned: Cannot find type System.Security.Cryptography.HashAlgorithm on Windows Phone 8.1 [2065]

Hi,

I'm trying to use this library on windows phone 8.1
I downloaded the windows Phone 8.0 version but when I try to use the library i get the following error:
Cannot find type System.Security.Cryptography.HashAlgorithm in module mscorlib.dll

And indeed System.Security.Cryptography is not available on Windows Phone (or windows 8 store).
Windows.Security.Cryptography however is available, but I couldn't find this class there as well...

Any idea what's going wrong?

Thanks,
Gal