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
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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?
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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
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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
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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
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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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