Vector dot product in Microsoft SEAL using the CKKS scheme
As suggested by Hilder Vitor Lima Pereira in the comments and KyoohyungHan on Github in the issue https://github.com/microsoft/SEAL/issues/138, it is possible to sum the elements with rotations:


  For example,
  {1, 2, 3, 4} is encrypted in a ciphertext.
  You can get encrypted {3, 4, 1, 2} using homomorphic rotation by index 2.
  With homomorphic addition, you have encrypted {4, 6, 4, 6}.
  After that, you can get encrypted {6, 4, 6, 4} using homomorphic rotation by index 1.
  Finally, you have encrypted {10, 10, 10, 10} with homomorphic addition which is the sum of the element in a ciphertext.