CAST Encryption

CAST is a family of block ciphers developed by Carlisle Adams and Stafford Tavares.

Key Generation

Generate a secure key and initialization vector (IV) for CAST encryption

Encrypt File

Upload a file and encrypt it with CAST

Decrypt File

Upload an encrypted file and decrypt it with CAST

About CAST Encryption

CAST is a family of block ciphers designed by Carlisle Adams and Stafford Tavares (hence the name CAST) in 1996. The most widely used variants are CAST-128 (also known as CAST-5) and CAST-256 (also known as CAST-6).

CAST-128 (CAST-5):
  • Block Size: 64 bits
  • Key Size: 40 to 128 bits (in 8-bit increments)
  • Rounds: 12 or 16 rounds (depending on key size)
  • Structure: Feistel network with complex round function
  • Status: Standardized in RFC 2144 and used in various applications including PGP
CAST-256 (CAST-6):
  • Block Size: 128 bits
  • Key Size: 128, 160, 192, 224, or 256 bits
  • Rounds: 48 rounds (12 quad-rounds)
  • Structure: Substitution-permutation network (SPN)
  • Status: Submitted as a candidate for the AES competition but not selected as a finalist
How CAST Works:

CAST-128:

  1. Uses a Feistel network structure with 16 rounds for 128-bit keys (12 rounds for shorter keys)
  2. Each round uses one of four different round functions, which include operations like:
    • Modular addition and subtraction
    • XOR operations
    • Fixed S-boxes (substitution boxes)
    • Circular rotations
  3. The key schedule generates 16 subkeys of 32 bits each, plus 16 rotation values

CAST-256:

  1. Extends CAST-128 to handle 128-bit blocks and longer keys
  2. Uses a substitution-permutation network with 48 rounds organized as 12 "quad-rounds"
  3. Each quad-round applies four different round functions to different parts of the data
  4. Uses the same basic operations as CAST-128 but with a more complex structure
Security and Applications:
  • Security: CAST-128 has withstood cryptanalysis well, with no practical attacks against the full cipher. CAST-256 was designed with an even higher security margin.
  • Applications: CAST-128 has been used in various security applications, including:
    • Pretty Good Privacy (PGP) for email encryption
    • GNU Privacy Guard (GPG)
    • Various VPN implementations
  • Licensing: CAST-128 was patented, but the patents have expired, making it free to use. CAST-256 is also free to use.
Note: While CAST-128 is still considered secure for many applications, modern systems typically prefer AES or other newer ciphers with larger block sizes for new implementations.