Handle security issue with OT extension

[jot2re]

A recent paper highlights an issue with the proof of security of the KOS15 OT extension which is used in Fresco. In particular see section 4.1.3. It seems the issues is not critical, but that the security is not as high as expected. As far as I can see we need to increase the computational security parameter with 33%, but even doing that does not provide a proof of security. Only handling the attack suggested in the paper. As a minimum we should increase the computational security by 50% and consider to switch to another OT extension without issues in the security proof.