Ok patriots, notebooks at the ready. Since we're all going to the gulag, it's time to brush up on your wartime opsec skills, or learn them if you're a first-timer.

Tradecraft, as the skillz of espionage are known, involves being able to communicate in a way which is seemingly only in one direction, so that the two parties are never able to be connected together.

The Numbers Station. Every day at a specific time, an FM antenna broadcasts a set of numbers. Anyone can listen in. Only one person with a pad of decoder numbers can use them to understand the message.

• https://www.numbers-stations.com/
• http://www.progressive-concepts.com/transmission-equipment/fm-antennas.html

Steganography. The 5th image on an Insta account this week, containing a boat or bicycle, contains a message in the file header.

• https://www.greycampus.com/blog/information-security/top-must-have-tools-to-perform-steganography

Short-range Radio (SRAC). A hollowed out piece of dead wood in a park has a receiver in it. As someone walks by it, a "burst" of data is transmitted to it.

• https://wps.prenhall.com/wps/media/objects/4035/4132489/TeleCom_Breger.pdf

Facial Recognition Blocking. Facial scans rely on being able to create a "map" of points on your face. Covid masks and screens work rather well.

• https://www.survivopedia.com/6-ways-to-defeat-facial-recognition/
• https://iq.opengenus.org/sobel-operator/

The Dead Letter Box. One or more remote locations are agreed which aren't suspicious to travel to. When something has been left there to be collected, a signal is also left. Like an orange peel in a flowerbed: five different positions of the peel explain which one. Or messages are left in the drafts folder of an email account.

• https://www.globaleaks.org/

The Cut Out. A middleman, patsy, go-between, or proxy who relays messages, without realising what they are sending, or that they are in the middle.

• https://www.wallstreetmojo.com/hawala/

The Duress Code. A pre-agreed word or phrase indicating a person is being forced to do something against their will, which does not trigger an alarm. Can be a phrase which is omitted from the greeting.

• https://www.lybrary.com/magic-mentalism-spiritism-two-person-codes-c-21_29_4033.html
• https://www.explorepsychology.com/barnum-effect/

The Broken Candle. We all know this one. An innocuous signal is published at a specified time schedule. If it does not appear, the publisher has been compromised.

• https://warrantcanaries.com/

The Security Ink It buys you time. not security. A person doing a newspaper crossword writes in the margin on page 17, and leaves it behind at the train station. The second picks it up and rips it out.

• https://austinpublishinggroup.com/forensicscience-criminology/fulltext/ajfsc-v4-id1061.pdf