Letter Number Code (A1Z26) A=1, B=2, C=3

The Letter-to-Number Cipher (or Number-to-Letter Cipher or numbered alphabet) consists in replacing each letter by its position in the alphabet, for example A=1, B=2, Z=26, hence its over name A1Z26.

A1Z26 encryption requires to count the positions/ranks of letters in the alphabet. If it is the Latin alphabet of 26 characters here is the correspondence table letter ↔ number/value:

Replace each letter with its position in the alphabet (A = 1, B = 2, … Z = 26) and use a separator character to space the numbers.

Decryption requires taking each number and replace it with the letter of same position in the alphabet: 1 = A, 2 = B, … 26 = Z, here is the corresponding table:

The crypted message is made of numbers between 1 and 26, sometimes the number 0 is used to code a space.

Numbers are usually separated by spaces or dashes.

The digit 5 for E is supposed to appear regularly for an English text.

This encryption is sometimes called alphanumeric code.

If the alphabet is shifted, it is common for clues of the form letter equals number (K=7) to be provided (common principle of cryptogram type games).

Shift of numbers: the alphabet can start with A = 0 (A0Z25) or A = 1, but also A = 65 or A = 97 (ASCII code).

Use of a supplementary character for space (often 0, more rarely 27)

Use of leading zeros to be able to concatenate numbers AB = 0102, else AB = 12 and 12 = L.

Use of a personalized, shifted abecedary (Caesar code) or even an inversion of the alphabet (A=26, Z=1)

Use of modulo 26 in order to get 1=A,2=B,…26=Z then 27=A, 28=B etc.

The A1Z26 encoding/decoding algorithm is as follows:// Pseudo code
function encrypt_A1Z26(text) {
dictionary = {"A":1, "B":2, . . ., "Z":26}
ciphertext = ""
foreach (letter in text) {
ciphertext += dictionary.replace(letter) + "-"
}
return ciphertext
}
function decrypt_A1Z26(text) {
dictionary = {1:"A", 2:"B", . . ., 26:"Z"}
text.split("-")
plaintext = ""
foreach (number in text) {
plaintext += dictionary.replace(number)
}
return plaintext
}
// Python
def encode_a1z26(text):
return " ".join(str(ord(c) - 64) for c in text.upper() if c.isalpha())
def decode_a1z26(numbers):
return "".join(chr(int(n) + 64) for n in numbers.split())