SecureNN is an implementation from the SecureNN paper. SecureNN is an extension of the Pond protocol. ie SecureNN is a superset of the SPDZ protocol. The main difference between SecureNN and SPDZ is exact Relu and Maxpooling layers. In SPDZ, Maxpooling is simply not supported, and Relu will be approximated.

Approximation can be quicker in some cases but it will break down when inputs are sufficiently large. This requires users to implement workaround techniques such as adding a Batchnorm layer before a Relu.