Cryptiana: Articles on Historical Cryptography

Various codes and ciphers used through history are described. See also my blog.

NOTICE (October 2026): It seems people are visiting this website for unsolved ciphers recently. While many articles herein mention unsolved ciphertexts, they may have already been solved because of the increased interest in the field since September 2026. I'm sorry the articles are not always up-to-date. I try to catch up with the latest status at "Unsolved Historical Ciphers". Please check up this page when you start to work on something and before publishing your results.

Early Japanese Codes and Ciphers

明治日本の暗号いろいろ (Japanese Codes and Ciphers during the Meiji Period)
明治期に使われた暗号盤いろいろ (Japanese Cipher Disks during the Meiji Period)
明治日本の外交暗号：1874-1885-1904 (Japanese Diplomatic Codes and Ciphers during the Meiji Period)
日露戦争中の日本の一外交暗号の概要判明 (Japanese Diplomatic Code during Russo-Japanese War)
明治・大正期の陸軍暗号 (Japanese Military Codes and Ciphers during the Meiji and Taisho Periods)
明治期の海軍暗号 (Japanese Naval Codes and Ciphers during the Meiji Period)
Codes and Ciphers of Imperial Japanese Army and Navy in the Meiji Period: 1874-1912
Early Japanese Diplomatic Codes: 1874-1933
明治末～昭和初期の暗号セキュリティー雑録 (Crypto-Security in Late-Meiji to Early-Showa Period)

Japanese Codes and Ciphers in the 1920s-1930s

A Specimen of Yardley's Deciphering of Japanese Diplomatic Code Jp (1921)
Japanese Reaction to Yardley's The American Black Chamber (1931)
ヤードレー『アメリカン・ブラック・チェンバー』の新聞報道（リンク集） (1931) (Newspaper articles on Yardley's American Black Chamber)
Development of the First Japanese Cipher Machine: RED (1927-1932)
映画紹介：The Red Machine（「レッド暗号機」）
Yardley's Diplomatic Novel, Red Sun of Nippon (1934)
昔の特許文献の探し方と戦前の暗号関係の特許（付：戦前の中間処理実例） (Pre-War Japanese Crypto-Patents)

Asian Cryptography

中国の暗号：1871-1945
Chinese Cryptography: 1871-1945
Solution of Two Chinese Cipher Telegrams Archived in Japan (1916) NEW
Yardley's Codebreaking of Book Cipher used by Pro-Japanese Traitors in China (1939)
Substitution Cipher for Hangul
Korean Cryptography

Tools

Frequency Count (with Microsoft Excel)
Bigram Count (with Microsoft Excel)
Listing Recurring Polygrams from Ciphertext (with Perl)
Creating a KWIC Index with Microsoft Excel
Creating a Contact Chart with Microsoft Excel

Miscellaneous

深川言葉　―　大河ドラマ「べらぼう」に出てきた遊里の暗号 (Concealment ciphers in Japanese culture) (in Japanese)
暗号兵だったやなせたかし (Anpanman) (in Japanese) (Introduction in English)
『大脱走』の暗号 Cipher behind The Great Escape (in Japanese)
連続殺人犯「ゾディアック」の暗号Z340、半世紀ぶりに解読 (Zodiac Ciphers) (in Japanese)
ゾディアックZ13の「解読」は本物か (Zodiac Cipher Z13) (in Japanese)
「ハードナッツ」の暗号（素因数分解指数暗号） (Factor Exponent Cipher from TV) (in Japanese)