Multi-tap Phone Cipher (SMS)

Multitap replaces a letter by repeated digits defined by the corresponding key code on a mobile phone keypad (This mode is used when writing SMS/Texto).

The correspondence table is:

Example: DCODE becomes 3222666333

This standard also has the name of E.161 created by the ITU Telecommunication Standardization Sector (ITU-T). It only sets letters from A to Z, other characters such as digits or lowercase uppercase distinctions are not normalized.

Multi-tap decryption consists in replacing groups of numbers by their corresponding letter, but if there is no separator, then it is necessary to test all the possibilities of words and only return the existing words in the dictionary.

Example: 2222 = AAAA or AAB or ABA or AC or BAA or BB or CA

The ciphered message is made of numbers with digits often repeated consecutively, between 1 and 3 times, there a few or none 1 or 0.

Variations of the multi-tap ABC can be created by varying the writing.

Example: A code such as 222 can be written 2*3, 2^3 or 23.

An over-encryption is possible by coding a message twice

Example: PHONE = 7446666633 = PGGMMMMMDD

Mobile phones have other typing techniques, such as T9 predictive text.

The first patent is from 1985. It has since been used in the majority of mobile phones keypad, had its heyday with the Nokia, and then disappeared with touch screens and smartphones type iphone.