This tutorial book is a collection of notes and sample codes written by the author while he was learning Blowfish cipher himself. Topics basic concepts of cipher and encryption; introduction of Blowfish cipher algorithm; 8366 Hex Digits of PI; Perl Crypt::Blowfish and Crypt::CBC, Crypt::CFB modules; OpenSSL Blowfish ciphers: bf-ecb, bf-cbc, bf-cfb, bf-ofb; PHP Mcrypt extension; Blowfish CFB-8 and OFB-8 operation modes. Updated in 2024 (Version v2.04) with minor changes.For latest updates and free sample chapters, visit https://www.herongyang.com/Blowfish.