Chapter 4 - AES question n answers rated A+

Chapter 4 - AESAES (Advanced Encryption Standard) - correct answer -most widely used symmetric cipher today -algorithm chosen by US NIST (Rijndael) -block cipher with 128-bit block size -3 supported key lengths: 128, 192, 256 bits -efficient in software and hardware -iterated cipher with 10/12/14 rounds -starts with key addition (128 bit sukey XORed to the state) -each round consists of "layers" -byte substitution layer -diffusion layer (shift rows, mix columns) -key addition - correct answer describe AES process -byte oriented cipher -state A (128 bit data chunk) can be arranged in 4x4 matrix with A0-15 denoting 16-byte input of AES - correct answer describe internal structure of AES byte, bit - correct answer AES steps are ___-oriented while DES is ___-oriented (byte or bit) AES - correct answer steps of ____: -round function for rounds 1 to n-1 -substitution -byte-wise permutation -mixing -XOR with key -in last round, mixcolumn transformation omitted s boxes - correct answer byte substitution layer consists of 16 _______ with properties: -identical for every round -only nonlinear elements of AES -bijective (one to one mapping of input/output) -input value has 8 bits (first 4 indicate row, last 4 indicate column -table contains substitute for those 8 bits diffusion - correct answer ____ layer: -provides ____ over all input state bits -consists of two sublayers shiftrows and mixcolumn -performs a linear operation on state matrices A, B shiftrows - correct answer ____ sublayer: input to output table -first row no shift -second row one position to the left shift -third row two to left -forth row three to left mixcolumn - correct answer ____ sublayer: -linear transformation which mixes each column of the state matrix -primary diffusion element -each 4byte column is considered a vector and multiplied by a fixed 4x4 matrix -generates 4 new bytes to replace original 4 bytes in that column -all arithmetic is done in the Galois field GF(2^8) key addition - correct answer ______ layer: -inputs: 16byte state matrix C, 16byte subkey k