ADVANCED ENCRYPTION STANDARD PREPARED BY: KRISTEN NAIR A/L SRIDERAN 012010030490 VIVIANNA MUJAN AK NICHOLAS 012010050424

INTRODUCTION The Advanced Encryption Standard(AES) is an encryption algorithm for securing sensitive but unclassified material by U.S Government agencies and as a likely consequence, may eventually become the real encryption standard for commercial transaction in the private sector. AES is based on a design principle known as a substitution permutation network. It is fast in both software and hardware. Unlike its predecessor, DES, AES does not use a feistel network.

INTRODUCTION A strong encryption algorithm need only meet only single main criteria: There must be no way to find the unencrypted clear text if the key is unknown, except brute force, example, to try all possible keys until the right one is found A secondary criterion must also be met: The number of possible keys must be so large it is computationally infeasible to actually stage a successful brute force attack in short enough a time.

METHOD IN ADVANCED ENCRYPTION STANDARD AddRoundKey: The AddRoundKey routine is simple XOR step. It is the step that incorporates the round key, a portion of the expanded key, into the plaintext. XOR- Exclusive-OR operation

METHOD IN ADVANCED ENCRYPTION STANDARD SubBytes: In the SubBytes step, each byte in the matrix is updated using an 8-bit substitution box, the Rijndael S-box. This operation provides the non-liearity in the cipher. The S-box used is derived from the multiplicative inverse over GF(28),known to have good non-linearity properties, the s-box is constructed by combining the inverse function with an invertible affine transformation. The S-box is also chosen to avoid any fixed points(and so is a derangement), and also any opposite fixed points. SBOX- Non linear substitution table used in several byte substitution transformations and in the key Expansion routine to perform a one-for-one substitution of a byte value. Affine transformation- A transformation consisting of multiplication by a matrix followed by the addition of a vector.

METHOD IN ADVANCED ENCRYPTION STANDARD ShiftRows Arranges the state in a matrix and then performs a circular shift for each row. This is not a bit wise shift. The circular shift just moves each byte one space over. A byte that was in the second position may end up in the third position after the shift. The circular part of it specifies that the byte in the last position shifted one space will end up in the first position in hte same row.

METHOD IN ADVANCED ENCRYPTION STANDARD MixColumns: This is perhaps the hardest step to both understand and explain. There are two parts to this step. This first will explain which parts of the state are multiplied against which parts of the matrix. The second will explain how this multiplication is implemented over what’s called a Galois Field.

CONCLUSION There is currently no evidence that AES has any weakness making any attack other than exhaustive search, example brute force. There are many pitfalls to avoid when encryption is implemented, and keys are generated. It is necessary to ensure each and every implementations security, but hard since it requires careful examination by experts. An information aspect of an evaluation of any specific implementation is determine that such an examination has been made, or can be conducted.