1 / 12

Advanced Encryption Standard

Advanced Encryption Standard. Reference: Stallings, Data and Computer Communications, 7th Edition ,Pearson/P-H, 2004. AES Background. 1997 --National Institute of Standards and Technology (NIST) issues a call for proposals.

pelham
Download Presentation

Advanced Encryption Standard

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Advanced Encryption Standard Reference: Stallings, Data and Computer Communications, 7th Edition,Pearson/P-H, 2004

  2. AES Background • 1997 --National Institute of Standards and Technology (NIST) issues a call for proposals. • 2001--AES issues as a federal information processing standards (FIPS 197)

  3. AES Requirements • Security Strength Equal to or Better than 3DES • Significantly More Efficient than 3DES • Symmetric Block Cipher • Block Length = 128 bits • Support for Key Lengths of 128, 192, and 256 bits

  4. Evaluation Criteria for AES Proposals • Security • Computational Efficiency • Memory Requirements • Hardware and Software Suitability • Flexibility

  5. The State and KeySchedule • Fig. 21.2 shows the AES algorithm structure. • Input is a 128 bit block (16 bytes) that is placed in the state array (Fig. 21.3) • The key is entered in a block and divided into key schedule words of 4 bytes/word. • The key schedule is an expansion of the key—eg, a 128 bit key is expanded into 44 key schedule words. • A square matrix of bytes is used by the standard to describe the state.

  6. Rounds and Transformation Stages • The encryption process executes a round function, Nr times, with the number of rounds (Nr) being dependent on key size. • The round function consists of four transformation stages. • SubBytes() • ShiftRows() • MixColumns() • AddRoundKey()

  7. Rounds and Transformation Stages (p.2) • The cipher begins with an AddRoundKey(). • All rounds then execute each of the transformations except the last round. • The MixColumns( ) transformation is not executed in the final round. • For a 128 bit key, there are 10 rounds. • 12 and 14 rounds are used with keys of 192 and 256.

  8. SubBytes ( ) Transformation • The substitute transformation is an S-Box process, that is independent of the key. • Each of the bytes of the State is replaced by a different byte, according to a table. • The table is fixed and derived from two transformations defined in the standard. • The table is an 8 x 8 array, indexed with the State byte.

  9. ShiftRows( ) Transformation • The ShiftRows() transformation is a permutation that is performed row by row on the State array, independently of the key. • The first row is not shifted. • The 2nd row is circularly shifted left 1 byte. • The 3rd row is circularly shifted left 2 bytes. • The 4th row is circularly shifted left 3 bytes.

  10. MixColumns() Transformation • The MixColumns( ) transformation manipulates each column of the state array. • The process can be described as a matrix multiplication of a polynomial and the state array. • This process does not depend on the key.

  11. AddRoundKey( ) Transformation • The AddRoundKey( ) transformation uses the key schedule word. • The process is a bitwise XOR of the columns of the state array, with the key schedule word.

  12. AES Decryption • AES decryption is accomplished using inverses of the transformations, in the appropriate order. • The AddRoundKey( ) is its own inverse when (since A  B  B = A).

More Related