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Securely Deleting Encrypted Data on Linux

In this scenario you are the Systems Administrator for a healthcare company. Your manager has tasked you with logging into the fileserver running CentOS Linux 7.7 and securely deleting some sensitive patient data, ensuring that it cannot be easily recovered. No other files should be altered.

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Path Info

Clock icon Intermediate
Clock icon 15m
Clock icon Jan 31, 2020

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Table of Contents

  1. Challenge

    Confirm File Is Readable

    Confirm the size and permissions of the file:

    [cloud_user@$host]$ sudo ls -l /mnt/patient.1

    Show the contents of the file:

    [cloud_user@$host]$ sudo cat /mnt/patient.1
  2. Challenge

    Fill Free Space

    Be sure to double check the path, as this command does no error checking and will overwrite data:

    [cloud_user@$host]$ sudo dd if=/dev/urandom of=/mnt/junk status=progress; sync
  3. Challenge

    Overwrite File

    The shred command is the simplest method. Specifying -x ensures that the filesize remains unchanged:

    [cloud_user@$host]$ sudo shred -x /mnt/patient.1

    If the shred command is not available, we can use the following dd command:

    [cloud_user@$host]$ sudo dd if=/dev/urandom of=/mnt/patient.1 bs=45 count=1 iflag=fullblock status=progress
  4. Challenge

    Confirm File Was Overwritten and Remove

    Show file contents:

    [cloud_user@$host]$ sudo cat /mnt/patient.1

    Remove file:

    [cloud_user@$host]$ sudo rm /mnt/patient.1
  5. Challenge

    Restore Free Space

    Remove junk file:

    [cloud_user@$host]$ sudo rm /mnt/junk

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