In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent. In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad). Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition. If the key is truly random, at least as long as the plaintext, never reused in whole or in part, and kept completely secret, then the resulting ciphertext will be impossible to decrypt or break. [Source: Wikipedia, https://en.wikipedia.org/wiki/One-time_pad]
In conjunction with the One Time Pad, the Trigraph is used to encrypt a plain text message into coded 5 character groups. The Trigraph itself is simple to use, requiring that the user intersect 2 known characters from the Key and Plaintext, and select the corresponding character to create the encrypted text for the message.
In the example below we'll look at using the Trigraph to encrypt a simple message that you want to meet the message recipient at the store at 9PM.
1st Row: Cipher key (ZDDAF QLSTX XCXEN FLYSQ)
2nd Row: Plaintext message (MEET ME AT NINE PM AT STORE)
3rd Row: Encrypted text (OSSGI FOOTH PIQVT CWNQF)
Result: OSSGI FOOTH PIQVT CWNQF
As you can see, if you were caught with the result, it would be impossible for anyone to know what was in the encrypted message. It is old-school, but it works and doesn't require anything but a cipher key, the encrypted text and a trigraph to send a secure message from one person to another (P2P).
Download Trigraph: http://www.echocq.com/blog/wp-content/uploads/2019/05/OTP.png
Generate Random 5 Character Groups: https://www.randomlists.com/random-letters?chars=ABCDEFGHIJKLMNOPQRSTUVWXYZ&length=5&qty=100&dup=false