CKKS security estimation for Palisade

Question

My question is rather practical and specific. I am trying to setup an efficient CKKS scheme in Palisade. To this end, the automatic choice for secure parameters has to be turned off and I rely on the LWE estimator which estimates the security of an LWE instance. Now, the estimator provides a security estimation for an LWE instance $\mathrm{LWE}(n,\alpha,q)$, where $n$ is the dimension/ring dimension, $\alpha$ depends on error distribution, and $q$ is the ciphertext modulus. However, in Palisade there seems to be no possibility to setup the error in CKKS (this is easily possible in BGV). This way, $\alpha$ remains unknown and the security can not be estimated.

Therefore, how is the error chosen in Palisade for CKKS and how can this value be accessed?

Answer 1

In PALISADE, CKKS is configured to use $\alpha = 8/q$ (using the definition of $\alpha$ in the LWE estimator). This corresponds to the standard deviation of $8/\sqrt{2\pi} \approx 3.19$. This value was chosen based on the HE security standard at https://homomorphicencryption.org/standard/

You can manually change this value from 3.19 to something else by modifying $\textbf{genCryptoContextCKKS}$ in https://gitlab.com/palisade/palisade-release/-/blob/master/src/pke/lib/cryptocontextfactory.cpp