Can a Vigenere Cipher be Broken without Key Repetition?

I've been interested in whether a Vigenere cipher without key repetition can be solved. If the key is random, it is a one-time pad and is theoretically unbreakable. On the other hand, if the key is a natural language text, I heard such a cipher (called a running key cipher) can be solved. But how?
I uploaded a new article about this: "Solving Running Key Ciphers (Manually/Digitally)".

A Florentine Polyalphabetic Cipher from the 1480s

I learned in a paper by Marco Vito that the instruction for a Florentine cipher from the 1480s prescribes its use as a polyalphabetic cipher. This is the only actual example of a polyalphabetic cipher before 1560 (not counting the treatises by Alberti and Trithemius as actual examples).
This induced me to collect specimens of polyalphabetic ciphers known to me as a new article, "Polyalphabetic Ciphers before 1600".

Japanese Cipher Disks during the Meiji Period

I uploaded a new article in Japanese about cipher disks used in Japan during the Meiij Period. At the time, Japan was just starting to use Western-style ciphers and the cipher disks were not used for a polyalphabetic cipher, but only for switching the monoalphabetic substitution table.
While some of these have already been mentioned in some of my articles, I sorted those with new materials I came across recently, including (1) telegrams in relation to the assassination attempt on the Tsarevich (1891) (Wikipedia) and (2) photos of actual cipher disks used in post offices.

Real Messages Encrypted by Japanese RED Machine

Two authentic messages encrypted by using RED (1937) are recorded in a document declassified by NSA (REF ID: A71152), which I recently learned from Jean-François Bouchaudy.
The messages are:
(1) Ambassador in Berlin ("Mushakoji" [Wikipedia]) to Foreign Minister in Tokyo (Arita [Wikipedia]), 4 January 1937 (ciphertext, raw decryption, English translation).
(2) From Tokyo to ambassador in Berlin, 8 January 1937 (ciphertext, raw decryption) with decryption in romaji and English translation (somehow dated "9 January 1937").

Bouchaudy learned of this document from George Lasry in June 2025, who quickly found the key to the two messages. Then, Bouchaudy succeeded in reproducing the decryption by the RED simulator he developed.
He reports the results on his website, in which I contributed in parsing the raw decryption of the first message into words in Japanese.

For people interested in ciphertext encrypted by RED, Bouchaudy "created" 9 problems in the form of historical correspondence among US codebreakers. He tells us they (not authentic RED messages) are based on the wiring of the examples given in Alan G. Konheim (2007), Computer Security and Cryptography (which deals with RED and PURPLE in Chapter 7).

Deavours and Kruth (1985), Machine Cryptography and Modern Cryptanalysis has a paragraph in RED (p.213), but Bouchaudy tells us it is different from RED because it "has no Period".

"Cipher Disk" before Alberti

I recently learned that before Leon Battista Alberti's treatise, there had been ideas similar to his cipher disk. In particular, Giovanni Fontana's disk for mnemonics looks very similar to Alberti's cipher disk, though there is no evidence Alberti knew this. (Another interesting thing about Fontana is that his ideas are described in a manuscript booklet almost entirely in cipher.)
I uploaded a short article about this: "Giovanni Fontana's "Cipher Disk" (ca. 1430) in an Encrypted Booklet". (This was delayed several weeks because of troubles of my PC....)