Substitution–permutation network

In <a href="/facts/Cryptography/e94PEVau">cryptography</a>, an SP-network, or substitution–permutation network (SPN), is a series of linked mathematical operations used in <a href="/facts/Block_cipher/MJywAyfQ">block cipher</a> algorithms such as <a href="/facts/Advanced_Encryption_Standard/HdXGBY2Q">AES (Rijndael)</a>, <a href="/facts/3-Way/ys51uHk9">3-Way</a>, <a href="/facts/Kalyna_(cipher)/ALqwpfdy"> Kalyna</a>, <a href="/facts/Kuznyechik/uRclFGnf">Kuznyechik</a>, <a href="/facts/PRESENT_(cipher)/gDMsJHlH">PRESENT</a>, <a href="/facts/Secure_and_Fast_Encryption_Routine/gfWYnLDr">SAFER</a>, <a href="/facts/SHARK/8MffJfmL">SHARK</a>, and <a href="/facts/Square_(cipher)/mQRozt3V">Square</a>.
Such a network takes a block of the <a href="/facts/Plaintext/tWnBDCgE">plaintext</a> and the <a href="/facts/Key_(cryptography)/5W5PAmT4">key</a> as inputs, and applies several alternating rounds or layers of <a href="/facts/Substitution_box/9xKgnLCF">substitution boxes</a> (S-boxes) and <a href="/facts/Permutation_box/QochB9Th">permutation boxes</a> (P-boxes) to produce the <a href="/facts/Ciphertext/luNTs4sY">ciphertext</a> block. The S-boxes and P-boxes transform (sub-)blocks of input <a href="/facts/Bit/S972NSaD">bits</a> into output bits. It is common for these transformations to be operations that are efficient to perform in hardware, such as <a href="/facts/Exclusive_disjunction/FHyr7hGQ">exclusive or</a> (XOR) and <a href="/facts/Bitwise_rotation/0gkqnUda">bitwise rotation</a>. The key is introduced in each round, usually in the form of "<a href="/facts/Round_key/H2klHRyU">round keys</a>" derived from it. (In some designs, the <a href="/facts/S-box/9xKgnLCF">S-boxes</a> themselves depend on the key.)
<a href="/facts/Decryption/16q29Fdv">Decryption</a> is done by simply reversing the process (using the inverses of the S-boxes and P-boxes and applying the round keys in reversed order).

Substitution–permutation network open-in-new

Substitution–permutation network