Tähestikukoodi

Tähestikukoodi is an Estonian term that translates to "alphabet code" or "letter code" in English. It refers to a simple substitution cipher where each letter of the alphabet is systematically replaced by another letter, a number, or a symbol. These codes are often used for basic obfuscation or in educational contexts to teach the principles of cryptography.

The most straightforward type of tähestikukoodi is a simple Caesar cipher, where each letter is shifted a fixed number of positions down the alphabet. For example, with a shift of three, 'A' becomes 'D', 'B' becomes 'E', and so on. More complex forms might involve a keyword to create a more varied substitution pattern, ensuring that letter frequencies are not as easily discernible.

Tähestikukoodi is generally considered a weak form of encryption. Its main vulnerability lies in frequency analysis, where the occurrences of each symbol in the ciphertext can be compared to the known frequencies of letters in the plaintext language to deduce the substitution key. Despite its simplicity, tähestikukoodi has been used historically in various forms, from ancient military communications to playful secret messages exchanged among friends. In modern times, its primary application is educational, serving as an accessible introduction to the fundamental concepts of coding and decoding.