# Some question about multiplication depth and security parameter

**URL:** <https://openfhe.discourse.group/t/some-question-about-multiplication-depth-and-security-parameter/1349>\
**Category:** FHE Use Cases\
**Created:** [June 13, 2024, 9:26am UTC](https://openfhe.discourse.group/t/some-question-about-multiplication-depth-and-security-parameter/1349 "2024-06-13T09:26:23Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![kenan](https://avatars.discourse-cdn.com/v4/letter/k/e495f1/32.png) [@kenan](https://openfhe.discourse.group/u/kenan)\
**Post date:** [June 13, 2024, 9:26am UTC](https://openfhe.discourse.group/t/some-question-about-multiplication-depth-and-security-parameter/1349/1 "2024-06-13T09:26:23Z")

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Question 1, I would like to ask how to reduce the multiplication depth. Initially, I set the multiplication depth to 30 because it is necessary to perform Chebyshev approximation and ciphertext comparison (CKKS → FHEW) on the ciphertext.

Question 2, I want to use a 128-bit security level, but under the condition of a multiplication depth of 30, the recommended ring size is very large. Is there any way to reduce the ring size? What are the recommended parameters for using a 128-bit security level in CKKS, such as scaleModSize, firstModSize, and multiplication depth?

Question 3, Can I initially set a smaller multiplication depth and then automatically increase the multiplication depth during the calculation process for operations such as comparing ciphertexts or computing some operations of the Chebyshev approximation?

Question Four, what is the difference between HEStd\_128\_quantum and HEStd\_128\_classic? Do they choose different ring dimensions?

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**Author:** ![evgen](https://avatars.discourse-cdn.com/v4/letter/e/85f322/32.png) [@evgen](https://openfhe.discourse.group/u/evgen)\
**Post date:** [June 30, 2024, 3:45pm UTC](https://openfhe.discourse.group/t/some-question-about-multiplication-depth-and-security-parameter/1349/2 "2024-06-30T15:45:20Z")

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Do you solve your questions?

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**Author:** ![ypolyakov](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/ypolyakov/32/47_2.png) [@ypolyakov](https://openfhe.discourse.group/u/ypolyakov)\
**Post date:** [June 30, 2024, 6:30pm UTC](https://openfhe.discourse.group/t/some-question-about-multiplication-depth-and-security-parameter/1349/3 "2024-06-30T18:30:00Z")

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These questions are too open-ended and not well-defined. I can point to introductory material on FHE, papers, or tutorials if this helps. I also suggest asking one question at a time (with a concrete description of the example/application).