Symmetric Encryption of IMEI with a nonce included
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For user registration purpose I need IMEI number to be entered on the application. However, I would like to encrypt this IMEI number so that user doesn't exactly know what is being entered on the app. Also, I am planning to include a nonce within, so that it is different every time user registers.

So my mobile app needs implement symmetrical encryption with nonce such that a 16 digit key (serial number) is generated. The key should be a simple string of number  or alphanumeric characters that user can enter in the app and  the IMEI number can be extracred back, in the backend.

Any recommendation on algorithm and implementation?