Topic summary
Round constant
Extracted from the Wikipedia article Round (cryptography).
Round constants
Inserting round-dependent constants into the encryption process breaks the symmetry between rounds and thus thwarts the most obvious slide attacks. The technique is a standard feature of most modern block ciphers. However, a poor choice of round constants or unintended interrelations between the constants and other cipher components could still allow slide attacks (e.g., attacking the initial version of the format-preserving encryption mode FF3).