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During (what we Americans call) the Vietnam War, American prisoners of war, often held in solitary confinement in adjacent cells in the Hanoi Hilton, would use

During (what we Americans call) the Vietnam War, American prisoners of war, often held in solitary confinement in adjacent cells in the Hanoi Hilton, would use the tap code extensively to talk to each other, sometimes carrying on long conversations, for example about ways to resist their captors. The article alludes to that but doesn't go into a lot of detail about that bit of history. (This is discussed in https://en.wikipedia.org/wiki/Tap_code https://en.wikipedia.org/wiki/Tap_code cited downthread by 'dmckeon.)

WalterBright 3y ago
If they're in adjacent cells, using a tap for dit and a scrape for dah should work.
- dcanelhas 3y ago
  In the film adaptation of "Let the right one in" they use this method.
qingcharles 3y ago
I was introduced to this tap code just after being incarcerated and used it often. A friend and I also modified it to be able to communicate in/out of solitary confinement as they had kiosks in each cell block allowing you to order commissary food. The kiosks had many bugs I found in the code, but they especially lacked any sane range checking, so you could enter orders for up to 9999 noodles for instance. We broke the knock code into two "byte" pairs. So HELL would be an order of 2315 Beef noodles and 3131 Chicken noodles. To access the orders between cellblocks it was necessary for the person in solitary to write their PIN (their username was their jail ID#) on a piece of toilet paper and pass it to someone outside solitary on a day they were in court. Then both sender and recipient could log into the same account from different cellblocks and read the order. Once read the order would be deleted and another order placed to reply to the message. At first I was out of solitary, but then I got sent for extortion (charge dropped after 10 days, story of my life) and while I was in solitary the staff went through my stuff and found some pieces of paper where I had sat encoding and decoding messages. The staff didn't have the table though and through the FOIA I managed to get access to their working out, but they never successfully decoded any of the undecoded messages they obtained from the kiosk. After that we rotated the encoding table 90 degrees in our heads to act as a very simple form of encryption in case they tried again. It took the authorities another 6 months to persuade the kiosk developers to add a piece of code which checked the jail ID# that was logging in against the cellblock they were in to make sure you couldn't log into an account if you weren't in the right cellblock.
- MetallicCloud 3y ago
  That's an amazing story!
- post-it 3y ago
  This sounds like something out of a Cory Doctorow book, I love it.
kybernetikos 3y ago
The game her story features some tap code. I hacked together a trainer https://projects.sys3.xyz/knockcode/index.html https://projects.sys3.xyz/knockcode/index.html

WalterBright 3y ago

If they're in adjacent cells, using a tap for dit and a scrape for dah should work.

dcanelhas 3y ago
In the film adaptation of "Let the right one in" they use this method.

qingcharles 3y ago

I was introduced to this tap code just after being incarcerated and used it often. A friend and I also modified it to be able to communicate in/out of solitary confinement as they had kiosks in each cell block allowing you to order commissary food. The kiosks had many bugs I found in the code, but they especially lacked any sane range checking, so you could enter orders for up to 9999 noodles for instance. We broke the knock code into two "byte" pairs. So HELL would be an order of 2315 Beef noodles and 3131 Chicken noodles. To access the orders between cellblocks it was necessary for the person in solitary to write their PIN (their username was their jail ID#) on a piece of toilet paper and pass it to someone outside solitary on a day they were in court. Then both sender and recipient could log into the same account from different cellblocks and read the order. Once read the order would be deleted and another order placed to reply to the message. At first I was out of solitary, but then I got sent for extortion (charge dropped after 10 days, story of my life) and while I was in solitary the staff went through my stuff and found some pieces of paper where I had sat encoding and decoding messages. The staff didn't have the table though and through the FOIA I managed to get access to their working out, but they never successfully decoded any of the undecoded messages they obtained from the kiosk. After that we rotated the encoding table 90 degrees in our heads to act as a very simple form of encryption in case they tried again. It took the authorities another 6 months to persuade the kiosk developers to add a piece of code which checked the jail ID# that was logging in against the cellblock they were in to make sure you couldn't log into an account if you weren't in the right cellblock.

MetallicCloud 3y ago
That's an amazing story!
post-it 3y ago
This sounds like something out of a Cory Doctorow book, I love it.

kybernetikos 3y ago

The game her story features some tap code. I hacked together a trainer https://projects.sys3.xyz/knockcode/index.html https://projects.sys3.xyz/knockcode/index.html