# Suggestion on error message

**URL:** <https://openfhe.discourse.group/t/suggestion-on-error-message/2312>\
**Category:** Library Questions\
**Tags:** feature-requests\
**Created:** [April 16, 2026, 1:12pm UTC](https://openfhe.discourse.group/t/suggestion-on-error-message/2312 "2026-04-16T13:12:29Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [April 16, 2026, 1:12pm UTC](https://openfhe.discourse.group/t/suggestion-on-error-message/2312/1 "2026-04-16T13:12:29Z")

</div>

Hi developers, i open a thread here as i can not open an issue in github

I’d like to suggest a minor change to the library which might help users. In particular, when one tries to evaluate a rotation in CKKS without first generating the corresponding key switching key, the library says something like:

`src/pke/lib/schemebase/base-leveledshe.cpp:l.404:EvalAutomorphism(): EvalKey for index [5] is not found.`

which i understand, however the index [5] does not correspond to the actual rotation, as in this case i was rotating by 128 (i think 5 is the index `i` such that `evalKeyMap.find(i)` returns the rot key corresponding to 128).

I think it would be great to tell the user the \* actual index \* that is missing so that it is way easier to fix:)

---

<div class="post-metadata">

**Author:** ![Caesar](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/caesar/32/63_2.png) [@Caesar](https://openfhe.discourse.group/u/Caesar)\
**Post date:** [April 17, 2026, 12:29pm UTC](https://openfhe.discourse.group/t/suggestion-on-error-message/2312/2 "2026-04-17T12:29:52Z")

</div>

Hi @narger - are you sure you were rotating by 128, not by 1?

---

<div class="post-metadata">

**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [April 17, 2026, 1:22pm UTC](https://openfhe.discourse.group/t/suggestion-on-error-message/2312/3 "2026-04-17T13:22:41Z")

</div>

hi @Caesar ! my bad, the error message is

`src/pke/lib/schemebase/base-leveledshe.cpp:l.404:EvalAutomorphism(): EvalKey for index [81409] is not found.`

and this corresponds to rotation by 128 in the ring 2^17