Symmetric Block Ciphers

Usual approaches

Large bit blocks for input, output, and key.

• 64, 128,256, etc.

Diffusion and confusion.

• Permutation, substitution, expansion, compression.

• Feistel networks, substitution-permutation networks.

• Iterations.

• Sub-keys (key schedules, round keys, etc).

Most common algorithms

• DES (Data Encryption Standard).

  • D = 64

  • K = 56

• IDEA (Integer Data Encryption Algorithm).

  • D = 64

  • K = 128

• AES (Advanced Encryption Standard) aka Rijndael.

  • D = 128

  • K = 128, 192, 256