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I'm researching details on a computer program, KOH, that was installed on the boot sector of a DOS or Windows 3.x PC circa 486 or 1995. I believe it was one of the earliest (maybe first for PC) examples of full disk encryption. The freeware program had two nicknames:

  • Potassium Hydroxide
  • King of Hearts

It asked for your decryption password on boot and stayed in memory. Hooking an interrupt for disk read/writes? While I know it worked with FAT file system, I don't remember if it was also compatible with LILO and Linux/Slackware. It used IDEA cipher block encryption for HDD and floppy. It was copyright 1995 by American Eagle Publications.

Can anyone provide any other information - first hand-accounts, recollections, sources or verification? Thank you

Cross posted on Cryptography Stack Exchange

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I don’t know how useful this is for you, but you can download KOH here (among other places), and access its documentation directly.

The documentation mentions that

At present, KOH is not compatible with advanced operating systems which do not go through the system BIOS to access the disk, and it is not compatible with IBM's boot manager. We intend to create drivers to make it work seamlessly with these operating systems eventually. Also, we are going to make a boot manager that will work with KOH available very soon.

This means it couldn’t be used with OS/2, Unix, or Linux. I don’t know whether this was ever fixed; there doesn’t seem to be a later version of KOH.

From comments on your Cryptography.SE crosspost, here are a couple of very interesting links:

KOH uses various virus-like techniques; in particular, it replicates itself (with user confirmation when encrypting a hard drive), to ensure that all floppy disks used in a protected system are encrypted by default.

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