a Basic substitution-Permutation Network Cipher The cipher that we shall use to present the concepts is a basic Substitution-Permutation Network(SPN) cach round consists of (1)substitution, (2 )a transposition of the bits(i.e, permutation of the bit positions ) and 3 )key mixing This basic structure was presented by Feistel back in 1973 and these basic operations are similar to what is found in des and many other modern ciphers, including rijndael 16
16 A Basic Substitution-Permutation Network Cipher • The cipher that we shall use to present the concepts is a basic Substitution-Permutation Network (SPN). • Each round consists of (1) substitution, (2) a transposition of the bits (i.e., permutation of the bit positions), and (3) key mixing. • This basic structure was presented by Feistel back in 1973 and these basic operations are similar to what is found in DES and many other modern ciphers, including Rijndael
plaintext Figure 1. Basic Substitution-Permutation Network(SPN) Cipher St S round I 17
17 Figure 1. Basic Substitution-Permutation Network (SPN) Cipher
Substitution In our cipher. we break the 16-bit data block into four 4-bit sub-blocks each sub-block forms an input to a 4x4S-box (a substitution with 4 input and 4 output bits we shall use the same nonlinear mapping for all s-boxes input outp Table 1. S-box Representation(in hexadecimal)
18 Substitution • In our cipher, we break the 16-bit data block into four 4-bit sub-blocks. Each sub-block forms an input to a 44 S-box (a substitution with 4 input and 4 output bits). • we shall use the same nonlinear mapping for all S-boxes. Table 1. S-box Representation (in hexadecimal)
Permutation The permutation portion of a round is simply the tranposition of the bits or the permutation of the bit positions input output Ha計 910111213141516 711154|81216 Table 2. permutation 19
19 Permutation • The permutation portion of a round is simply the tranposition of the bits or the permutation of the bit positions. Table 2. Permutation
Key mixing In our cipher. we break the 16-bit data block into four 4-bit sub-blocks each sub-block forms an input to a 4 x4 S-box(a substitution with 4 input and 4 output bits ) we use a simple bit-wise exclusive-or between the key bits In our cipher, we shall assume that all bits of the subkeys are independently generated and unrelated
20 Key Mixing • In our cipher, we break the 16-bit data block into four 4-bit sub-blocks. Each sub-block forms an input to a 44 S-box (a substitution with 4 input and 4 output bits). we use a simple bit-wise exclusive-OR between the key bits. • In our cipher, we shall assume that all bits of the subkeys are independently generated and unrelated