Lecture5.pptx - Data Integrity Computer Security...

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edithcowancollege.edu.au navitas.com Data Integrity Computer Security

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edithcowancollege.edu.au navitas.com Last Week……. encrypt decrypt Cipher text plaintext shared secret key shared secret key Communication channel Sender Recipient Attacker (eavesdropping) plaintext
edithcowancollege.edu.au navitas.com Data Integrity The validity and trustworthiness' of data Data may lose its integrity due to… Human errors Errors during data transmission over a network Software bugs Malware Hardware malfunctions Natural disasters

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edithcowancollege.edu.au navitas.com Ensuring Integrity via Parity Parity bits The letter A will be sent over a serial connection ASCII A in binary is 0100 0001 We have decided to use even parity which means that the total number of 1’s must be even So the binary sequence will be 0100 0001 0 The receiver knows we are using even parity If number of 1’s is even then no errors occurred But what if 2 errors occurred during transmission?
edithcowancollege.edu.au navitas.com Ensuring Integrity via Parity Parity bits cont… Original binary sequence was 0100 0001 0 Receiver got 0100 0010 0 Since parity was even, receiver assumed that no errors had occurred Receiver got binary sequence 0100 0010 0100 0010 in ASCII is the letter B What if the attack was deliberate?

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edithcowancollege.edu.au navitas.com Ensuring Integrity via Checksum Checksum – at senders end A file (1,151 bytes) will be sent over the Internet Using a checksum of 1 byte gives 256 values 1,151(file size)/256 = 4.496 (rounded down to 4) 4 x 256 = 1,024 1,151 – 1,024 = 127 The checksum value of 127 is added to the file
edithcowancollege.edu.au navitas.com Ensuring Integrity via Checksum Checksum – at receivers end A file (1,056 bytes) is received 1,056(file size)/256 = 4.125 (rounded down to 4) 4 x 256 = 1,024 1,056 – 1,024 = 32 The checksum value 32 does not match the original An attacker could also specifically modify the file to retain the original size

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edithcowancollege.edu.au navitas.com Data Integrity Checking Parity bits and Checksum are both susceptible to malicious and accidental faults and errors To ensure data integrity we need a method which is fault tolerant
edithcowancollege.edu.au navitas.com Cryptographic Hash Functions A strong way of assuring the integrity of a digital object Digital object could be; A document An executable program Any other collection of bits A paragraph of text A hash function takes the object as an input and outputs a ‘hash’ or ‘digest’

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edithcowancollege.edu.au navitas.com Cryptographic Hash Functions A complex, mathematical algorithm (formula) MD4 ,MD5, MD6 SHA1, SHA256, SHA512, SHA3 RIPEMD160, RIPEMD320 PANAMA TIGER And many others
edithcowancollege.edu.au navitas.com Message-Digest Algorithm 5 (MD5) Developed by Ron Rivest in 1991 Outputs 128 bit hash values Widely used in legacy applications Considered academically broken Faster than SHA-1

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