# Bug in Multiparty Scenario with EvalSum()

**URL:** https://openfhe.discourse.group/t/bug-in-multiparty-scenario-with-evalsum/1224
**Category:** Library Questions
**Tags:** questions, bugs
**Created:** [April 23, 2024, 8:26pm UTC](https://openfhe.discourse.group/t/bug-in-multiparty-scenario-with-evalsum/1224 "2024-04-23T20:26:34Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![moghit02](https://avatars.discourse-cdn.com/v4/letter/m/eb9ed0/32.png) [@moghit02](https://openfhe.discourse.group/u/moghit02)
#### Post date: [April 23, 2024, 8:26pm UTC](https://openfhe.discourse.group/t/bug-in-multiparty-scenario-with-evalsum/1224/1 "2024-04-23T20:26:34Z")

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I made some investigations into multiparty architecture. I used the tckks-interactive-mp-bootstrapping-Chebyshev.cpp example. I just changed the line where the ChebyshevSeries is calculated to EvalSum(…)  
I always get a decryption error because approximation error is too high. Since EvalSumKeys are also generated in this example, the decryption should actually work, am I right?

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<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 24, 2024, 2:37pm UTC](https://openfhe.discourse.group/t/bug-in-multiparty-scenario-with-evalsum/1224/2 "2024-04-24T14:37:01Z")

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Correct, there is a problem in the `EvalSumKeys` generation logic, specifically this [line](https://github.com/openfheorg/openfhe-development/blob/d73c38619afe9424de5fc960713480dbaa26fdf8/src/pke/examples/tckks-interactive-mp-bootstrapping-Chebyshev.cpp#L227).

If you change it to:

```auto
auto evalSumKeysJoin2 = cryptoContext->MultiAddEvalSumKeys(evalSumKeysJoin, evalSumKeysC, kp3.publicKey->GetKeyTag());

```

`EvalSum` should work.

We will fix this issue in the upcoming release, thank you for reporting it.