lec-10-aes-ccmp - 802.11SecurityAESCCMP ShambhuUpadhyaya...

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Shambhu Upadhyaya 1 802.11 Security – AES-CCMP 802.11 Security – AES-CCMP Shambhu Upadhyaya Wireless Network Security CSE 566 (Lecture 10)
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Shambhu Upadhyaya 2 AES Advanced Encryption Standard Symmetric block cipher, published in 2001 Intended to replace DES and 3DES - DES is vulnerable to differential attacks - 3DES has slow performances Requires coprocessor, therefore new hardware  deployment The AES Cipher: - Block length is limited to 128 bit - The key size can be independently specified to  128, 192 or 256 bits
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Shambhu Upadhyaya 3 AES-CCMP AES is a block cipher  RSN security protocol build around AES is  called AES-CCMP (Counter Mode-CBC  MAC Protocol) CCMP defines a set of rules which uses  AES for encryption and protection of  802.11 data AES to CCMP what RC4 is to TKIP
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Shambhu Upadhyaya 4 AES Overview AES is a block cipher Combines 128 bit blocks of data along with a key  to produce ciphertext Based on the Rijndael algorithm 802.11i’s implementation of the algorithm limits  both the key and block size to 128 bits Uses various  Modes of Operation  to convert a  continuous data stream to blocks of data
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Shambhu Upadhyaya 5 Modes of Operation Electronic Code Book (ECB) - Takes input message one block at a time and encrypts  each block sequentially using the same key - Can be implemented both in a parallel and serial  fashion - Has some problems Massage may not be exactly aligned with the block  boundaries so padding of the block may be required Has a security problem that if two blocks have the  same data then the output of the encryption process  produces the same ciphertext, hence leaking some  information
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Shambhu Upadhyaya 6 Electronic Code Book Encryption Initial Message Broken into Blocks Each block Encrypted Reassembled into Encrypted Message Serial Computation E E E E E Message AES Encryption Ciphertext Parallel Computation
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Shambhu Upadhyaya 7 Counter Mode Does not use the AES cipher directly to encrypt the data Instead, it encrypts an arbitrary value called counter and  XORs it with data to produce the ciphertext 1 E XOR 2 E XOR 3 E XOR 4 E XOR 5 E XOR 6 E XOR 7 E XOR Message Counter AES XOR Ciphertext
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