# FHE Questions **URL:** https://openfhe.discourse.group/c/fhe-questions/18.md [Latest](https://openfhe.discourse.group/latest.md) · [Categories](https://openfhe.discourse.group/categories.md) · [Tags](https://openfhe.discourse.group/tags.md) --- ## [About the FHE Questions category](https://openfhe.discourse.group/t/about-the-fhe-questions-category/27)
**Author:** [@iquah](https://openfhe.discourse.group/u/iquah)\ **Replies:** 0
For questions related to general FHE (note: this is not meant for questions related to the OpenFHE library) --- ## [Hello from Ethiopia - New OpenFHE Community Member](https://openfhe.discourse.group/t/hello-from-ethiopia-new-openfhe-community-member/2382)
**Author:** [@Ibnutesfaye](https://openfhe.discourse.group/u/Ibnutesfaye)\ **Replies:** 0\ **Last updated:** [September 8, 2026, 4:01pm UTC](https://openfhe.discourse.group/t/hello-from-ethiopia-new-openfhe-community-member/2382 "2026-09-08T16:01:49Z")
Hello everyone, My name is Abdurezak Tesfaye, and I am an Information Systems student from Ethiopia. I recently started learning OpenFHE and Fully Homomorphic Encryption (FHE). I am passionate about privacy-preserving … --- ## [FHE And Databases](https://openfhe.discourse.group/t/fhe-and-databases/2321)
**Author:** [@KitchM](https://openfhe.discourse.group/u/KitchM)\ **Replies:** 3\ **Last updated:** [May 26, 2026, 5:19pm UTC](https://openfhe.discourse.group/t/fhe-and-databases/2321 "2026-05-26T17:19:36Z")
Can FHE be used to query an encrypted database and to add encrypted records, and it so, is this trivial or an intensive process? Thank you. --- ## [Understanding the CKKS encoding algorithm](https://openfhe.discourse.group/t/understanding-the-ckks-encoding-algorithm/2310)
**Author:** [@j2kun](https://openfhe.discourse.group/u/j2kun)\ **Replies:** 3\ **Last updated:** [April 14, 2026, 1:11pm UTC](https://openfhe.discourse.group/t/understanding-the-ckks-encoding-algorithm/2310 "2026-04-14T13:11:20Z")
I’d like to understand OpenFHE’s choices around the packed CKKS encoding algorithm \[1\]. My naive understanding of CKKS encoding is that you: Ensure/extend the input vector to satisfy a conjugate symmetry property Appl… --- ## [Revocability of private key shares](https://openfhe.discourse.group/t/revocability-of-private-key-shares/2305)
**Author:** [@svetlana](https://openfhe.discourse.group/u/svetlana)\ **Replies:** 1\ **Last updated:** [March 30, 2026, 2:35pm UTC](https://openfhe.discourse.group/t/revocability-of-private-key-shares/2305 "2026-03-30T14:35:23Z")
Hello, for multiparty scenario, if one private‑key share is lost or leaked, the entire key set (all shares + public key + evaluation keys) must be regenerated, right? This is just to doble check, Thank you --- ## [Question about adding a new FHE scheme that natively supports MatMul without encoding](https://openfhe.discourse.group/t/question-about-adding-a-new-fhe-scheme-that-natively-supports-matmul-without-encoding/2306)
**Author:** [@ManhBui](https://openfhe.discourse.group/u/ManhBui)\ **Replies:** 1\ **Last updated:** [March 30, 2026, 12:58pm UTC](https://openfhe.discourse.group/t/question-about-adding-a-new-fhe-scheme-that-natively-supports-matmul-without-encoding/2306 "2026-03-30T12:58:29Z")
Hi OpenFHE team, Over last two years, I’m a OpenFHE’s user which mostly utilizing the library for my research on optimizing MatMul and Non-Linear functions in CKKS for Neural Networks. Recently, after experiencing the D… --- ## [Question on Two Implementation of Composite Rescaling](https://openfhe.discourse.group/t/question-on-two-implementation-of-composite-rescaling/2269)
**Author:** [@JianmingTong](https://openfhe.discourse.group/u/JianmingTong)\ **Replies:** 3\ **Last updated:** [January 28, 2026, 5:01pm UTC](https://openfhe.discourse.group/t/question-on-two-implementation-of-composite-rescaling/2269 "2026-01-28T17:01:14Z")
Hi! I found the current composite rescaling is implemented by iteratively dropping the last moduli until the number of dropped moduli hit the level (i.e. the composite degree), as detailed in this link: Would there be … --- ## [The difference between TFHE testvector and OpenFHE testvector](https://openfhe.discourse.group/t/the-difference-between-tfhe-testvector-and-openfhe-testvector/2270)
**Author:** [@Transformer](https://openfhe.discourse.group/u/Transformer)\ **Replies:** 1\ **Last updated:** [January 28, 2026, 1:09am UTC](https://openfhe.discourse.group/t/the-difference-between-tfhe-testvector-and-openfhe-testvector/2270 "2026-01-28T01:09:39Z")
I’ve recently been reading the source code of TFHE and OpenFHE, but I have many questions regarding the construction of test polynomials, especially since OpenFHE’s implementation differs significantly from TFHE’s. I wou… --- ## [RLWE secret key and decryption function for RLWE ciphertexts in binfhe(FHEW/TFHE)](https://openfhe.discourse.group/t/rlwe-secret-key-and-decryption-function-for-rlwe-ciphertexts-in-binfhe-fhew-tfhe/2244)
**Author:** [@Transformer](https://openfhe.discourse.group/u/Transformer)\ **Replies:** 3\ **Last updated:** [January 5, 2026, 7:06pm UTC](https://openfhe.discourse.group/t/rlwe-secret-key-and-decryption-function-for-rlwe-ciphertexts-in-binfhe-fhew-tfhe/2244 "2026-01-05T19:06:18Z")
I’m studying Blind Rotation in FHEW/TFHE, and I’ve found that if I modify the loop order of the Blind Rotation, for example, changing the loop order of i from \[0, 1, ..., n-1\] to \[n-1, n-2, ..., 0\], the values ​​of a and… --- ## [How exactly is the scaling factor adjusted in general functional bootstrap using ckks](https://openfhe.discourse.group/t/how-exactly-is-the-scaling-factor-adjusted-in-general-functional-bootstrap-using-ckks/2216)
**Author:** [@Joseph](https://openfhe.discourse.group/u/Joseph)\ **Replies:** 7\ **Last updated:** [November 17, 2025, 3:37pm UTC](https://openfhe.discourse.group/t/how-exactly-is-the-scaling-factor-adjusted-in-general-functional-bootstrap-using-ckks/2216 "2025-11-17T15:37:25Z")
Hi, I’m trying to understand the paper General Functional Bootstrapping using CKKS (https://eprint.iacr.org/2024/1623.pdf). In line 3 of the algorithm 1 in the paper, the ciphertext ct\_1, encrypting \\frac{q'\_0}{p}m(X… --- ## [Question about general functional bootstrapping using CKKS](https://openfhe.discourse.group/t/question-about-general-functional-bootstrapping-using-ckks/2198)
**Author:** [@Joseph](https://openfhe.discourse.group/u/Joseph)\ **Replies:** 2\ **Last updated:** [October 30, 2025, 9:17am UTC](https://openfhe.discourse.group/t/question-about-general-functional-bootstrapping-using-ckks/2198 "2025-10-30T09:17:45Z")
Hi everyone, I’ve been reading the paper on general functional bootstrapping using ckks(General Functional Bootstrapping using CKKS) and also looking at the accompanying implementation. Both the paper and the code ment… --- ## [Implement Inner Product Using Coefficient Encoding](https://openfhe.discourse.group/t/implement-inner-product-using-coefficient-encoding/2190)
**Author:** [@sihyeok](https://openfhe.discourse.group/u/sihyeok)\ **Replies:** 4\ **Last updated:** [October 17, 2025, 9:13am UTC](https://openfhe.discourse.group/t/implement-inner-product-using-coefficient-encoding/2190 "2025-10-17T09:13:41Z")
I am trying to compute the sum of squares of plaintext coefficients using coefficient encoding in BFV without Key Switching. The idea is to exploit the identity: f(X)f(X^{-1}) = a\_0^2 + a\_1^2 + \\cdots + a\_{n-1}^2 + \\l… --- ## [About CKKS bootstrapping](https://openfhe.discourse.group/t/about-ckks-bootstrapping/2189)
**Author:** [@JoeRaft](https://openfhe.discourse.group/u/JoeRaft)\ **Replies:** 2\ **Last updated:** [October 8, 2025, 5:55pm UTC](https://openfhe.discourse.group/t/about-ckks-bootstrapping/2189 "2025-10-08T17:55:42Z")
Hello everyone, this is my first post over here and I would like to ask for a confirmation, hope it is not off-topic. I know that – e.g. in FHEW-like – the bootstrapping requires an encryption of the secret key. Neverth… --- ## [Question about the design idea of FBT](https://openfhe.discourse.group/t/question-about-the-design-idea-of-fbt/2182)
**Author:** [@Haow\_P](https://openfhe.discourse.group/u/Haow_P)\ **Replies:** 3\ **Last updated:** [September 26, 2025, 3:32pm UTC](https://openfhe.discourse.group/t/question-about-the-design-idea-of-fbt/2182 "2025-09-26T15:32:35Z")
Hi, Yuriy I understand that the FBT follows the PBS structure of TFHE/FHEW, where BFV ciphertext corresponds to TRLWE ciphertext in TFHE and CKKS ciphertext corresponds to TLWE ciphertext in TFHE (correct me if I misund… --- ## [How to choose Secret Key Distribution](https://openfhe.discourse.group/t/how-to-choose-secret-key-distribution/1477)
**Author:** [@JuriusStep](https://openfhe.discourse.group/u/JuriusStep)\ **Replies:** 5\ **Last updated:** [September 8, 2025, 6:50am UTC](https://openfhe.discourse.group/t/how-to-choose-secret-key-distribution/1477 "2025-09-08T06:50:32Z")
There are 3 Secret Key Distributions: GAUSSIAN UNIFORM\_TERNARY SPARSE\_TERNARY Im original paper of CKKS or CKKS RNS there are 3 Distributions too? why do you use for UNIFORM\_TERNARY as default and GAUSSIAN for examp… --- ## [Calculating Security Level and logq in OpenFHE](https://openfhe.discourse.group/t/calculating-security-level-and-logq-in-openfhe/2149)
**Author:** [@seanmoris](https://openfhe.discourse.group/u/seanmoris)\ **Replies:** 3\ **Last updated:** [August 25, 2025, 9:32am UTC](https://openfhe.discourse.group/t/calculating-security-level-and-logq-in-openfhe/2149 "2025-08-25T09:32:27Z")
Hi all, I’m working on a CKKS application in OpenFHE and trying to determine the appropriate security level, but I’m a bit unsure about how to calculate it properly. I’ve been referring to the Homomorphic Encryption Sta… --- ## [Is there a symmetric encryption form for RLWE-based FHE scheme?](https://openfhe.discourse.group/t/is-there-a-symmetric-encryption-form-for-rlwe-based-fhe-scheme/2146)
**Author:** [@pikaqiu](https://openfhe.discourse.group/u/pikaqiu)\ **Replies:** 1\ **Last updated:** [August 21, 2025, 5:00pm UTC](https://openfhe.discourse.group/t/is-there-a-symmetric-encryption-form-for-rlwe-based-fhe-scheme/2146 "2025-08-21T17:00:28Z")
As stated in the title --- ## [Rotation by encrypted value](https://openfhe.discourse.group/t/rotation-by-encrypted-value/2102)
**Author:** [@karlo\_73](https://openfhe.discourse.group/u/karlo_73)\ **Replies:** 2\ **Last updated:** [July 31, 2025, 11:16am UTC](https://openfhe.discourse.group/t/rotation-by-encrypted-value/2102 "2025-07-31T11:16:34Z")
Hi all, I was wondering if there is any way to perform rotations by an encrypted value (blind rotation?) in any of the schemes using batching (mainly CKKS)? Of course, normal rotations are a standard feature, but has an… --- ## [Approximate Modular Reduction during Bootstrapping](https://openfhe.discourse.group/t/approximate-modular-reduction-during-bootstrapping/2119)
**Author:** [@seyda](https://openfhe.discourse.group/u/seyda)\ **Replies:** 1\ **Last updated:** [July 31, 2025, 8:31am UTC](https://openfhe.discourse.group/t/approximate-modular-reduction-during-bootstrapping/2119 "2025-07-31T08:31:27Z")
Hi everyone, I am trying to understand the approximate modular reduction step during bootstrapping. I suppose OpenFHE implements the scaled cosine technique by Han & Ki. By assuming K = 512 and r = 3, I tried approximat… --- ## [Modulus overflow and Chebyshev approximation](https://openfhe.discourse.group/t/modulus-overflow-and-chebyshev-approximation/2088)
**Author:** [@ilemenn](https://openfhe.discourse.group/u/ilemenn)\ **Replies:** 6\ **Last updated:** [July 23, 2025, 2:36pm UTC](https://openfhe.discourse.group/t/modulus-overflow-and-chebyshev-approximation/2088 "2025-07-23T14:36:32Z")
Hello, I am currently trying to perform a Chebyshev approximation to evaluate 1/sqrt(x). I had the same problem as in this other forum question: Weird behavior on Chebyshev - #4 by ypolyakov While choosing a larger mul… --- ## [ComparisonViaSchemeSwitching with EvalNOT](https://openfhe.discourse.group/t/comparisonviaschemeswitching-with-evalnot/2105)
**Author:** [@TomDing](https://openfhe.discourse.group/u/TomDing)\ **Replies:** 1\ **Last updated:** [July 21, 2025, 3:57pm UTC](https://openfhe.discourse.group/t/comparisonviaschemeswitching-with-evalnot/2105 "2025-07-21T15:57:54Z")
Hello everyone. I just try to understand the ComparisonViaSchemeSwitching function in our example code “/src/pke/examples/scheme-switching.cpp”. And I encountered a problem. For example, If I want to use EvalNOT to cha… --- ## [How to transform a ciphertext from one slot count to another without decryption](https://openfhe.discourse.group/t/how-to-transform-a-ciphertext-from-one-slot-count-to-another-without-decryption/2097)
**Author:** [@haohaohao](https://openfhe.discourse.group/u/haohaohao)\ **Replies:** 1\ **Last updated:** [July 19, 2025, 5:37pm UTC](https://openfhe.discourse.group/t/how-to-transform-a-ciphertext-from-one-slot-count-to-another-without-decryption/2097 "2025-07-19T17:37:14Z")
Hello everyone! I’m working on a problem where I need to transform a ciphertext’s effective slot count without decrypting and re-encrypting. Context: I have a ciphertext with numSlots = 8 containing the plaintext: \[0.… --- ## [Computing 1/x Over \[-100, 100\] with EvalDivide](https://openfhe.discourse.group/t/computing-1-x-over-100-100-with-evaldivide/2048)
**Author:** [@yuucyf](https://openfhe.discourse.group/u/yuucyf)\ **Replies:** 9\ **Last updated:** [June 11, 2025, 1:46pm UTC](https://openfhe.discourse.group/t/computing-1-x-over-100-100-with-evaldivide/2048 "2025-06-11T13:46:45Z")
Hello! I’m working on computing the reciprocal, 1/x , for values x within the range \[-100, 100\] using OpenFHE primitives. I am using OpenFHE to compute 1/x, but the value of x is in the interval \[-100, 100\]. However, s… --- ## [openFHE support comparison with ckks scheme?](https://openfhe.discourse.group/t/openfhe-support-comparison-with-ckks-scheme/2024)
**Author:** [@yuucyf](https://openfhe.discourse.group/u/yuucyf)\ **Replies:** 2\ **Last updated:** [May 12, 2025, 10:02am UTC](https://openfhe.discourse.group/t/openfhe-support-comparison-with-ckks-scheme/2024 "2025-05-12T10:02:13Z")
does openFHE support some function that can do the comparison of 2 encrypted numbers? (ckks scheme, not TFHE/FHEW) --- ## [Scaling factor for bootstrap matrices](https://openfhe.discourse.group/t/scaling-factor-for-bootstrap-matrices/2002)
**Author:** [@yhh](https://openfhe.discourse.group/u/yhh)\ **Replies:** 5\ **Last updated:** [April 29, 2025, 3:10am UTC](https://openfhe.discourse.group/t/scaling-factor-for-bootstrap-matrices/2002 "2025-04-29T03:10:09Z")
Hi, I am reading the function EvalBootstrapSetup for ckks, and I was wondering if scaleEnc and scaleDec is necessary for general homomorphic slots-coeff switching. Thanks for your time! --- ## [How does function AdjustCiphertext work?](https://openfhe.discourse.group/t/how-does-function-adjustciphertext-work/1695)
**Author:** [@yhh](https://openfhe.discourse.group/u/yhh)\ **Replies:** 5\ **Last updated:** [April 24, 2025, 5:14am UTC](https://openfhe.discourse.group/t/how-does-function-adjustciphertext-work/1695 "2025-04-24T05:14:42Z")
Hi, I am trying to learn the bootstrapping procedure, and would like to learn what does AdjustCiphertext in bootstrapping procedure do, especially the adjustmentFactor = (targetSF / sourceSF) \* (modToDrop / sourceSF) \* … --- ## [Does Homomorphic Constant Multiplication Require Additional Circuit Depth?](https://openfhe.discourse.group/t/does-homomorphic-constant-multiplication-require-additional-circuit-depth/1292)
**Author:** [@oksuman](https://openfhe.discourse.group/u/oksuman)\ **Replies:** 8\ **Last updated:** [April 10, 2025, 4:41am UTC](https://openfhe.discourse.group/t/does-homomorphic-constant-multiplication-require-additional-circuit-depth/1292 "2025-04-10T04:41:36Z")
Hello, I have a question about the minimum required level of ciphertexts to evaluate a homomorphic circuit. Specifically, I am wondering if constant multiplication in homomorphic encryption consumes a level. When perfo… --- ## [How multiplicative depth is being calculated for any polynomial approximation?](https://openfhe.discourse.group/t/how-multiplicative-depth-is-being-calculated-for-any-polynomial-approximation/1964)
**Author:** [@Jason](https://openfhe.discourse.group/u/Jason)\ **Replies:** 1\ **Last updated:** [March 28, 2025, 7:46am UTC](https://openfhe.discourse.group/t/how-multiplicative-depth-is-being-calculated-for-any-polynomial-approximation/1964 "2025-03-28T07:46:32Z")
Q1) I am implementing comparison with help of polynomial approximations. If the degree of polynomial is 9 or 7, the M. depth will be 4 and if the degree of polynomial is 3,5, the M. depth will be 3. How EvalPoly function… --- ## [Confirmation on Cooley-Tukey NTT Results](https://openfhe.discourse.group/t/confirmation-on-cooley-tukey-ntt-results/1921)
**Author:** [@Yusaku\_suzuki](https://openfhe.discourse.group/u/Yusaku_suzuki)\ **Replies:** 9\ **Last updated:** [March 27, 2025, 7:27am UTC](https://openfhe.discourse.group/t/confirmation-on-cooley-tukey-ntt-results/1921 "2025-03-27T07:27:52Z")
I understand that OpenFHE’s NTT implementation uses the Cooley-Tukey NTT. \[Code Link\] L302: void NumberTheoreticTransformNat\::ForwardTransformToBitReverseInPlace I would like to verify the correctness of its… --- ## [Is there a reference to CKKS proxy re-encryption used in openFHE?](https://openfhe.discourse.group/t/is-there-a-reference-to-ckks-proxy-re-encryption-used-in-openfhe/930)
**Author:** [@crazyRobert](https://openfhe.discourse.group/u/crazyRobert)\ **Replies:** 6\ **Last updated:** [March 26, 2025, 3:06pm UTC](https://openfhe.discourse.group/t/is-there-a-reference-to-ckks-proxy-re-encryption-used-in-openfhe/930 "2025-03-26T15:06:43Z")
Hello， I read the OpenFHE : Open-Source Fully Homomorphic Encryption Library, which introduces the proxy re-encryption of CKKS is a little brief, and its reference is only the proxy re-encryption of BV and NRTU, as if t… [Next page](https://openfhe.discourse.group/c/fhe-questions/18.md?page=1)