I am trying to generate a preseed file for automating the Ubuntu installation process.I want full disk encryption with the help of preseed having the pass-phrase included in the preseed.I wrote this:d-i partman-auto/method string cryptod-i partman-crypto/passphrase password helloworldd-i partman-crypto/passphrase-again password helloworldit is giving me error:unable to generate key file.I have tried many links but none helped:https://askubuntu.com/questions/24079/full-disk-encryption-with-preseedhttps://askubuntu.com/questions/305176/preseed-with-lvm-and-crypto-fails-with-an-error-occured-while-creating-the-keyf?rq=1but every time I got the same error.The thing is when I do it without the help of any preseed everything works fine.I want to know how to write a preseed for full disk encryption.I also referred to Ubuntu documentation,  but that also did not help. And this guide is not having much information for writing a preseed for encryption
unable to create key file. ubuntu installation error
ubuntu;preseed