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Cryptography and the Internet Daryl Banttari

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Introduction n Cryptography u There are two kinds of cryptography in this world: cryptography that will stop your kid sister from reading your files, and cryptography that will stop major governments from reading your files. This book is about the latter. --Bruce Schneier, preface, Applied Cryptography, Second Ed

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Topics of Discussion n Types of Cryptography n Applications to the Internet u SSL u Digital Signatures u Digital Signatures and SSL u Encryption and Authentication (PGP)

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Types of Cryptography n Cryptographically Strong Hash Functions (MD5) n Symmetric Key (Conventional) Encryption n Public Key Encryption

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The MD5 Hash Algorithm n Turns an arbitrary string into a 128-bit Message Digest or Hash n Always creates the same hash when given the same string n Impossible * to create a string from a hash or to alter a string and produce the same hash n Commonly used to verify that files are unaltered *Impossible: read Practically Impossible. It is believed to require operations to produce a message that would create a given digest. Hash("Hello1"): 7A6D1B13498FB5B3085B2FD Hash("Hello2"): B83099B8CE596F31F2F60C8FD4D72826 Hash("Hello3"): E1C0F BE86F96BD CCA0

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Symmetric Encryption n Proven and Secure n Fast n Uses the same key to decrypt as was used to encrypt n Requires out of band communication to exchange the key

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Public Key Encryption n Pioneered by Whitfield Diffie and Martin Hellman in n Data encrypted with the Public key can only be decrypted with the Private key, even by the encrypter n Data encrypted with Private key can only be decrypted by the Public key n Commonly used to exchange a conventional session key n Public key encryption algorithms include RSA, DSA, Diffie-Hellman, Blowfish

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SSL n Secure Server gives its Public key to the client n The client generates a conventional Session key n The client encrypts Session key with servers Public key n The rest of the communication uses Session key for speed

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Digital Signatures n MD5 Hash created of document n Hash in encrypted with Private key and appended to document n If the hash you decrypt using the senders Public key matches your own hash of the document: u The document must have been unaltered in transit u The document must have come from the sender n The combination of hash and private key is a Digital Signature

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SSL Certificate Signing n Encryption does not equal authentication n Some means needed of ensuring consumer that they are sending their credit card number to the people they expect, not some lookalike Web server n Verisign et al diligently ensure the public key belongs to a given organization u Attach organization info and expiration date to public key u Digitally sign public key with attached info u Public key of major certificate signers shipped with browsers

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Encryption and/or Authentication n PGP is an open, reasonably easy method of applying digital signatures and encryption to e- mail n People and organizations can sign a message that can then can be verified for authenticity by their public key n PGP uses session keys like SSL, so messages can be encrypted to multiple recipients without multiplying size of message- think of a keyed safe with multiple lock-boxes attached n You must have public key of recipient to encrypt an to them, which makes encryption to mailing lists, newsgroups, etc. unfeasible

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PGP Web of Trust n Anyone can upload keys to Key Servers-- even fake keys n If you can verify that a key belongs to its owner, you can sign that key, indicating that you have verified ownership n The Web of Trust is established by people signing other peoples keys; if you trust Person A to diligently verify identity of keys, and Person A signed Person Bs key, then you can trust that Person Bs key is authentic

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ColdFusions hash() Function n Available with CF4.5 n Generates md5 hashes of strings in hex format (use char(32) to store) n Useful for storing passwords so they cant be read or recreated n Append an arbitrary string to salt the password hash to prevent hash dictionary attacks Hash("Hello1"): 7A6D1B13498FB5B3085B2FD Hash("Hello2"): B83099B8CE596F31F2F60C8FD4D72826 Hash("Hello3"): E1C0F BE86F96BD CCA0

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Summary n An understanding of why encryption works is not necessary for an understanding of how it works n Although encryption and digital signature technology seem daunting, the processes are conceptually simple

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What do I do with this info? n Hash passwords n Use encryption and authentication methods for secure processes n Evangelize!

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