Blowfish and Twofish

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• both developed by Bruce Schneier as a replacement for DES
• reference designs are in the public domain
  • widely used
• both are Feistel substitution-permutation designs
  • only successful attack is the birthday attack (aka SWEET32) in HTTPS context
    • able to recover plaintext from ciphertext for ciphers using a 64-bit block size
    • thus, GnuPG recommends that as long as Blowfish is not used on files larger than 4GB, it is secure
• Twofish
  • derives from Blowfish’s design
  • was one of five finalists in the AES competition
  • is included in the OpenPGP standard RFC 4880