Caesar Cipher
The Caesar cipher is one of the oldest and best-known encryption methods. Used by Julius Caesar around 58 BC to protect Roman military communications, this method shifts each letter a fixed number of positions in the alphabet. Historically, Caesar used a shift of 3 positions (A→D, B→E, etc.). Despite its simplicity, it was effective for centuries when most of the population was illiterate.
Example with shift 3: "HELLO" → "KHOOR"
ROT13
ROT13 is a variant of the Caesar cipher with a fixed shift of 13 positions. Its particularity is that applying ROT13 twice consecutively returns the original text, since the Latin alphabet has 26 letters. Currently used in internet forums to hide spoilers, puzzle answers or potentially offensive content. It offers no real security, only obfuscates the text.
Example: "HELLO" → "URYYB" (applying ROT13 again → "HELLO")
Atbash Cipher
Atbash is a Hebrew encryption system dating from 600-500 BC. Its name comes from the first and last letters of the Hebrew alphabet (Aleph-Tav-Beth-Shin). The method reverses the alphabet: the first letter is replaced by the last, the second by the penultimate, etc. It appears in the Bible, where some names are encrypted with this method. It is one of the first documented examples of substitution cryptography.
Example: "HELLO" → "SVOOL" (H↔S, E↔V, L↔O, O↔L)
Vigenère Cipher
Developed by Giovan Battista Bellaso in 1553 and later attributed to Blaise de Vigenère, this method was considered "le chiffre indéchiffrable" (the indecipherable cipher) for three centuries. It uses a repeated key to determine different shifts for each letter, creating a polyalphabetic cipher much more secure than Caesar. It was not broken until 1863 by Friedrich Kasiski. It was widely used in diplomatic and military communications until the 20th century.
Example with key "KEY": "HELLO" → Each letter uses a different shift
Simple Substitution
Simple substitution cipher replaces each letter with another consistently, using a random substitute alphabet. This method was very popular during the Renaissance. Mary, Queen of Scots used a substitution cipher to conspire against Queen Elizabeth I, but it was decrypted through letter frequency analysis, leading to her execution in 1587. This method demonstrates the importance of cryptanalysis in history.
Example: Normal alphabet vs. random alphabet
Base64
Base64 is not an encryption method but an encoding scheme developed to represent binary data in ASCII text format. Created in the 1980s to facilitate data transmission through protocols that only supported text (such as email). It is widely used in web development to embed images in HTML/CSS and in modern APIs to transmit data. It provides no security, only converts the data format.
Example: "Hello" → "SGVsbG8="
XOR (Exclusive OR)
XOR cipher uses the XOR (exclusive OR) logical operation to combine text with a key. It is one of the fastest methods computationally and forms the basis of many modern algorithms. Its unique property is that applying XOR twice with the same key returns the original text. Used in military communications during the Cold War and still present in modern security protocols like TLS. With short keys it is vulnerable, but with random keys the same length as the message (one-time pad) it is theoretically unbreakable.
Example: Text XOR Key = Encrypted (Encrypted XOR Key = Text)
Text Reversal
Reversing text (writing backwards) is one of the simplest obfuscation methods. Although trivial with modern tools, historically Leonardo da Vinci used mirror writing in his personal notebooks, writing right to left. This made casual reading of his notes and drawings difficult. It offers no real security but is useful for educational demonstrations and puzzles.
Example: "HELLO WORLD" → "DLROW OLLEH"