Ciphers · TrithemiusTrithemius Cipher +0 +1 +2

Each next letter is shifted one place further along the alphabet than the previous one: the first by 0, the second by 1, the third by 2 and so on. Spaces, digits and punctuation do not advance the count. HELLO becomes HFNOS: H stays, E becomes F, L becomes N, the second L becomes O. The alphabet wraps around, so after Z comes A again.

Caesar uses one shift for the whole text, so it can be found by trying all 25 options. Trithemius gives every letter its own shift, so equal letters encrypt differently: AAA becomes ABC. The ciphertext no longer follows the letter frequencies of the language. But Trithemius has no key either: the rule is known, so anyone who knows the cipher can read the text.

A square of alphabets where each row is shifted by one letter from the row above. The row number is the shift, the column is the plain letter, and the cell where they meet is the cipher letter. Trithemius encrypted the first letter with the first row, the second with the second and so on. The same table later became the basis of the Vigenère cipher.

In Trithemius's own scheme the first letter did not change: it was encrypted with the first row of the table, where the shift is zero. Some textbooks and contests start the count at 1, and then the first letter is already shifted. If your answer does not match the expected one, tick “Start the shift at 1”. Another frequent cause is the alphabet, so check that too.

Johannes Trithemius was a German abbot, historian and scholar of the late 15th and early 16th centuries. He described his system in “Polygraphia”, finished in 1508 and printed in 1518, after his death. It is considered the first printed book on cryptography. Trithemius also wrote “Steganographia”, a treatise on secret writing disguised as a book about spirits.

Shift the letters the other way: the first by 0, the second back by 1, the third back by 2 and so on. Open the “Decrypt” tab, paste the text and check the alphabet. If the text still does not read, try “Start the shift at 1” — both variants appear in puzzles. A Russian text also depends on whether ё counts as a letter.