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Advanced encryption standard (aes)
- 1. ADVANCED ENCRYPTION STANDARD (AES) Presented By: Faraz Ahmad Roll No: 12905 MS IT (Evening) Department of IT, GCUF
- 2. ADVANCED ENCRYPTION STANDARD • How was AES created? • What is AES? • AES Design • Key Size and No. of Rounds • AES Structure • Process of decryption in AES • Security attacks possible on AES
- 3. HOW WAS AES CREATED? • AES competition • Started in January 1997 by NIST(National institute of standards and technology) • 4-year cooperation between • U.S. Government • Private Industry • Academia Why? • Replace Triple DES as it was so slow key size 168 bits • Provide an unclassified, publicly disclosed encryption algorithm, available royalty-free, worldwide
- 4. WHAT IS AES? • It is a symmetric key encryption algorithm. • It was originally called “Rijndael Cipher” after the name of the developers. • AES is a block cipher encrypt 128bits (16 bytes) of data at a time. • It treats the 16 bytes as a grid of 4x4. Messages which are longer than 128 bits are broken into blocks of 128 bits. (Each block is encrypted by same steps separately)
- 5. WHAT IS AES? (CONT.) • If the message is not the divisible by the block length, then dummy data (padding) is added. E.g. if the message is 425 bytes, you need 7 bytes of padding to make the message 432 bytes long. 432 is divisible by 16.
- 6. AES DESIGN
- 7. KEY SIZE AND NUMBER OF ROUNDS • Three key sizes can be used in AES and depending on key sizes the number of rounds in AES changes. Standard key size in AES is 128 bits and no of rounds are 10. • For AES encryption two sub keys are generated and in 1st round a round key is added. No. Key Size No of Rounds 1. 128 bits 10 2. 192 bits 12 3. 256 bits 14
- 9. AES STRUCTURE • For 128 bits plain text and 128 bits key is used and 10 rounds are performed on plain text to find the cipher text. • First of all 10 round keys are generated for each round there is separate round key. • But in first round an extra round key which is initial round is added to the round and then transformation is started. • Transformations are: • Substitute Bytes • Shift Rows • Mix Columns • Add Round Key • Last round does not has mix column transformation in both encryption and decryption.
- 10. AES STRUCTURE • Each Round consists of following stages:
- 11. PROCESS OF DECRYPTION IN AES • Add round key of 10th round of plain text as initial round key in the 1st round of decryption process in AES. • Then reverse the stages of round 10 of encryption process that are first shift rows and substitute bytes transformation of round 10 of encryption process and then perform inverse column mixing. • Use this answer as a round key of round 2 in decryption process. • By applying this reverse scenario get the original plain text.
- 12. SECURITY ATTACKS POSSIBLE ON AES • Related-key attack • On July 1, 2009, Bruce Schneier blogged about a related-key attack on the 192-bit and 256-bit versions of AES, discovered by Alex Biryukov and Dmitry Khovratovich, which exploits AES's somewhat simple key schedule and has a complexity of 2119. • XSL attack • The XSL attack is a method of cryptanalysis for block ciphers. The attack was first published in 2002 by researchers Nicolas Courtois and Josef Pieprzyk. It has caused some controversy as it was claimed to have the potential to break the AES cipher faster than an exhaustive search. Since AES is already widely used in commerce and government for the transmission of secret information, finding a technique that can shorten the amount of time it takes to retrieve the secret message without having the key could have wide implications.
Editor's Notes
- Related Key attack: In cryptography, a related-key attack is any form of cryptanalysis where the attacker can observe the operation of a cipher under several different keys whose values are initially unknown, but where some mathematical relationship connecting the keys is known to the attacker. For example, the attacker might know that the last 80 bits of the keys are always the same, even though he doesn't know, at first, what the bits are. This appears, at first glance, to be an unrealistic model; it would certainly be unlikely that an attacker could persuade a human cryptographer to encrypt plaintexts under numerous secret keys related in some way. https://en.wikipedia.org/wiki/Related-key_attack XSL attack: In cryptography, the eXtended Sparse Linearization (XSL) attack is a method of cryptanalysis for block ciphers. The attack was first published in 2002 by researchers Nicolas Courtois and Josef Pieprzyk. It has caused some controversy as it was claimed to have the potential to break the Advanced Encryption Standard (AES) cipher, also known as Rijndael, faster than an exhaustive search. Since AES is already widely used in commerce and government for the transmission of secret information, finding a technique that can shorten the amount of time it takes to retrieve the secret message without having the key could have wide implications. The method has a high work-factor, which unless lessened, means the technique does not reduce the effort to break AES in comparison to an exhaustive search. Therefore, it does not affect the real-world security of block ciphers in the near future. Nonetheless, the attack has caused some experts to express greater unease at the algebraic simplicity of the current AES. In overview, the XSL attack relies on first analyzing the internals of a cipher and deriving a system of quadratic simultaneous equations. These systems of equations are typically very large, for example 8,000 equations with 1,600 variables for the 128-bit AES. Several methods for solving such systems are known. In the XSL attack, a specialized algorithm, termed eXtended Sparse Linearization, is then applied to solve these equations and recover the key. The attack is notable for requiring only a handful of known plaintexts to perform; previous methods of cryptanalysis, such as linear and differential cryptanalysis, often require unrealistically large numbers of known or chosen plaintexts. https://en.wikipedia.org/wiki/XSL_attack