intro to cryptography definitions
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Intro to Cryptography Definitions Cryptography Cryptanalysis - PowerPoint PPT Presentation

Intro to Cryptography Definitions Cryptography Cryptanalysis Cryptology CRYPTOGRAPHY Plaintext Cyphertext More definitions block cipher stream cipher hash function shared key public key digital signature


  1. Intro to Cryptography

  2. Definitions • Cryptography • Cryptanalysis • Cryptology

  3. CRYPTOGRAPHY Plaintext Cyphertext

  4. More definitions • block cipher • stream cipher • hash function • shared key • public key • digital signature scheme

  5. Caesar Cipher • Rotate all letters by a fixed amount. • Htruzyjw xhnjshj nx fbjxtrj

  6. Vigenère Cipher • Fixed short pad • Plain: tobeornottobethatisthequestion • Key: runrunrunrunrunrunrunrunrunrun • KIOVIEEIGKIOVNURNVJNUVKHVMGZIA

  7. Playfair Cipher P A L M E lo rd gr an vi lx le sl et te rz R S T O N B C D F G MT TB BN ES WH TL MP TA LN NL NV H I K Q U V W X Y Z

  8. Exercises • Caesar Cipher: Zgo dgfy vg qgm osfl lzwkw ewkksywk lg jwesaf kwujwl • Vigenère: Encrypt “Computer science is fun” with “secure” • Playfair: Same as above

  9. One Time Pad • Provably perfectly secret • Pad as long as plaintext • Pad perfectly random • Pad only used precisely once • Red Phone

  10. One-Way Function • Given the output, you cannot compute the input in polynomial time. One-way Function Plaintext Cyphertext Cyphertext Plaintext

  11. One-Way Functions • Password hashing • Code books • others?

  12. Public Key Crypto Mailbox Letter

  13. Public Key Crypto Plaintext Cyphertext What if only one person could decipher all the cipher texts?

  14. Public Key Crypto • Each person has a key pair • public key — published for all the world to see • private key — decrypts messages • Anyone can encrypt a message with a public key • Only the owner can decrypt messages

  15. Digital Signatures • Sign a message with a private key • Anybody can verify with my public key • Public key widely published

  16. Issues • How do we know if a cypher is “good”? • How do we avoid usability weaknesses? • Do we plan on using existing devices in our scheme? • How to we model adversarial behaviors? • How do we verify that our adversaries are covered?

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