# The error with CKKS Mul

**URL:** <https://openfhe.discourse.group/t/the-error-with-ckks-mul/280>\
**Category:** Library Questions\
**Created:** [December 9, 2022, 11:50am UTC](https://openfhe.discourse.group/t/the-error-with-ckks-mul/280 "2022-12-09T11:50:54Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![hamm](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hamm](https://openfhe.discourse.group/u/hamm)\
**Post date:** [December 9, 2022, 11:50am UTC](https://openfhe.discourse.group/t/the-error-with-ckks-mul/280/1 "2022-12-09T11:50:54Z")

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![2022-12-09 194631](https://canada1.discourse-cdn.com/flex031/uploads/openfhe/original/1X/9772e9f4e74b6df966633375d0214cce9eef2bb8.png)  
 ![image](https://canada1.discourse-cdn.com/flex031/uploads/openfhe/original/1X/fe9cba8a5f1b9832980fa767be3ebb7af8c71f42.png)

Regarding ckks multiplication, I would like to ask what preparations need to be made before multiplying two ciphertexts.？

My error: /openfhe-development/src/pke/lib/cryptocontext.cpp:93 You need to use EvalMultKeyGen so that you have an EvalMultKey available for this ID

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**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:** [December 9, 2022, 3:14pm UTC](https://openfhe.discourse.group/t/the-error-with-ckks-mul/280/2 "2022-12-09T15:14:31Z")

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You need to make sure that you have generated the relinearization key before performing multiplication.  
Check this [procedure](https://github.com/openfheorg/openfhe-development/blob/main/src/pke/examples/simple-real-numbers.cpp#L147) in the simple CKKS demonstrative example which generates the relinearization key.