# CKKS drop_level operation on polynomial that drops RNS frames. This can naturally be extended to ciphertexts as pair of polynomials. The plaintext of a ciphertext is invariant to drop_level of ciphertext because the plaintext coefficients are smaller than a single frame and drop_level is linear operation. you need only to ignore frame that are droped, all the other frame compute the same operations pointwise. $ \begin{align} ct &=(a,b) \\ decrypt(ct)&=a*s-b = m \\ drop\_level(ct)&=(drop\_level(a),drop\_level(b)) \\ decrypt(drop\_level(ct))&=drop\_level(a)*s-drop\_level(b) \\ &=drop\_level(a*s-b)=m \end{align} $ ## Created 2025-12-18 14:30