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experts. I am working on a story that involves a terabyte portable drive that has been encrypted by Person 1 and needs to be decrypted by Person 2 (Person 1 is deceased by that point).

Person 1 and Person 2 attended the same school and graduated with computer science degrees. Person 2 is the more capable. Person 1 is the more impatient.

  1. What process should Person 2 follow to figure out the encryption model used in the drive?
  2. What flaw in the encryption would allow Person 2 to decrypt the drive - the flaw could be generated by Person 1's impatience to get the task done.
  3. How long do you think the decryption process would take, and what equipment would Person 2 need to have to perform the task? Assume limited resources, so no quantum computer available.
  4. How long would it take for Person 1 to encrypt such a drive, and what equipment would he need to get that task done? Again, no quantum computer allowed.

Any help will be deeply appreciated and I'm sure will allow me to create a more 'realistic' situation for the two characters involved. Thank you ahead of time for your time and consideration.

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Well, in real life, the most plausible situation would be that Person 1 picks a well-known disk encryption application, which encrypts things based on a password (which he picks based on his experience in school).

Person 2 guesses the application (or the application leaves some fingerprints on the disk, for example, a cleartext application that allows you to enter the password and 'unlock' the disk), and then guesses the password (based on their shared experience).

Of course, this isn't a very sexy (or sophisticated) scenario - just the most realistic. If you were looking for something that would give you an excuse for Person 2 to dive into cryptography, this isn't it.

Whether this works for you (as an author) would depend on what you want the reader to get out of this (e.g. that Person 2 is really quite technically adept, for example)

And, to answer your questions (at least for this scenario):

  1. What process should Person 2 follow to figure out the encryption model used in the drive?

Really up to you - these possibilities are all plausible:

  • having person 2 know enough about person 1 that they're likely to use a specific application (e.g. they're a MicroSquirt(tm) fan boy and so likely to use MicroSquirt's disk encryptor)
  • just guessing it (and maybe having to go through several possibilities)
  • seeing evidence on the disk
  1. What flaw in the encryption would allow Person 2 to decrypt the drive - the flaw could be generated by Person 1's impatience to get the task done.

In this scenario, choosing an easily guessable password (to make it memorable; a password such as qasQ-zD-1zu3iL2b6kAtGYMwSR/uZMyy/Apn$A1s is secure, but not very memorable; a password such as GoOrangeAndBlue is memorable, but perhaps not as secure to someone who went to that school).

  1. How long do you think the decryption process would take, and what equipment would Person 2 need to have to perform the task? Assume limited resources, so no quantum computer available.

Again, up to you. It may be that person 2 would need to go through billions of potential passwords to find the right one (and so would need some nontrivial amount of equipment), or he might guess it at the first couple of tries.

  1. How long would it take for Person 1 to encrypt such a drive, and what equipment would he need to get that task done? Again, no quantum computer allowed.

Not long at all - the task really is limited by how fast you can read/write the drive...

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  • $\begingroup$ Thanks for the answer. It's really appreciated. $\endgroup$
    – Fritz loebl
    Commented Jul 2 at 11:57
  • $\begingroup$ @Fritzloebl: BTW: have you selected a title for your story (assuming it gets published)? I might want to grab a copy when you're done... $\endgroup$
    – poncho
    Commented Jul 2 at 13:34
  • $\begingroup$ "seeing evidence on the disk" may not be sexy, but is extremely realistic. E.g. MicroSquirt's disk encryptor does not attempt to hide that it's being used. Same for many other encryption products. In fact, very few solutions around attempt to hide that; I can only name TrueCrypt and Veracrypt that fo do. $\endgroup$
    – fgrieu ♦
    Commented Jul 2 at 15:51
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If you want something catchy for a story, you might want something that is inherently weak, and possibly historical. The "Bass-O-Matic" cipher and skit come to mind.

Regarding 1 and 2, if your encryption is good, it is indistinguishable from random data. So, if you want to bait someone into looking at something, make it so it's not close to random.

Regarding 3 and 4, it's really fast once you get going. Most hard drives are encrypted with something called XTS that uses AES, and you don't notice any lag as it's in hardware.

Also, instead of a drive specifically, I'd use "dd" to data dump the drive into a file, but you also need to know that the "file system" is on the drive.

Good luck with your story.

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  • $\begingroup$ Thanks for the answer. I'll take the details into account. $\endgroup$
    – Fritz loebl
    Commented Jul 2 at 11:57

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