Multi-tap Phone (SMS)

The multi-tap code is the name given to the historic technique of texting/writing SMS on the first mobile phones with a keyboard of 10-12 numeric keys (before the advent of touch keyboards and T9). Each key corresponds to several letters and the user must press the same key multiple times to select the desired letter.

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:

The standard only defines the letters A to Z; other characters such as numbers or uppercase are not standardized.

Multi-tap decryption consists in replacing groups of numbers by their corresponding letter.

However, if there is no separator between groups of digits, then it is necessary to test all word possibilities.

— The message consists of numbers, often with digits repeated consecutively.

— The group size with repeats varies from 1 to 4 digits.

— The message contains few (or no) 1s or 0s.

— With new smartphones, this mode has become obsolete and is often used as a simplistic cipher.

— Any references to retro telephones (Nokia 3310, Bi-Bop, etc.), old dial phones, or keypads (beep) are clues.

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

An over-encryption is possible by coding a message twice

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 (numpad), had its heyday with the Nokia GSM, and then disappeared with touch screens and smartphones like iPhone.