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55 lines
1.5 KiB
Markdown
55 lines
1.5 KiB
Markdown
---
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title: "05-crypography"
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aliases:
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tags:
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- lecture
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- comp210
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---
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# news
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- zodiac killer code cracked
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- twitter leak
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# Brief history
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- study of secret messages
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- confidentiality of [cia-triad](notes/cia-triad.md)
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- also small role in integrity (authentication of message, and sender)
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- history of cyprtopgraphy is interwined with information technology
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Language use for communication seems to be part of human nature: perhaps the use of covert lanuage is too
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## need for confidentiality
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"nothing to hide: nothing to fear" look at edward snowdens corrolary
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We all have legit needs for privacy. Cryptography provides technical measure for ensuring this privacy.
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## history
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- caesar cipher
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- simple substitution scheme (rotation)
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- vulnerable to cryptanalysis
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- key is a single integer
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- symmetrical (same key for encrypt and decrypt)
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- so ciphertext has the same patterns as the plaintext e.g., letter frequencies
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- this leads to cryptanalysis: systematic ways of determining the encryption scheme
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- modern ciphers aim to make the cipher text resemble *noise* (random data)
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# General process
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- encrypt
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- plaintext + key => ciphertext
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- key is a secret
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- decrypt
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- ciphertext + key => plaintext
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mathmatically
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- c = e(p, k)
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- p = d(c, k)
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# Terminology
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- copy later
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# Plaintext
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refers to unencypted message. In the digital age the messages are often not plain text (ascii, unicode, etc).
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digital crypto schemes normally work on the binary data (images, .docs, .txt, mp4 etc.)
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