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E1. Security

GR01E - Electronic Commerce Overview. Module 1 Technology:. E1. Security. Data security Hacker resistance Fault Tolerance Intrusion control and detection SSL Policies …. What is SSL/TSL?. Secure Socket Layer/Transport Layer Security Runs commonly on top of TCP/IP

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E1. Security

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  1. GR01E - Electronic Commerce Overview Module 1 Technology: E1. Security

  2. Data security Hacker resistance Fault Tolerance Intrusion control and detection SSL Policies …

  3. What is SSL/TSL? • Secure Socket Layer/Transport Layer Security • Runs commonly on top of TCP/IP • A protocol that implements • - privacy against eavesdroppers through encryption of messages • - message integrity trough hash function • - authentication through digital signatures • e.g., connect to https, ssmtp, spop3 (each has a unique port number)

  4. New standard for secure communication over the internet January 1999: Draft version 1.0 (http://www.ietf.org) Netscape SSL Secure Socket Layer Microsoft PCT Private Communication Technology IETF: TLS Internet Engineering Task force Based on SSL 3.0 Goals: • `Cryptographic security’ (including privacy and authentication • Interoperability • Extensibility • Relative efficiency

  5. TLS Protocols: TLS handshake protocol: TLS record protocol: Negotiation of - Session identifier packaging of data to be transported - Compression method - Cipher specification - Master key - Peer certificate

  6. Authetication: either - both parties - server authentication - no authentication

  7. Security Analysis

  8. However: -How secure is the cryptographic protocol? (e.g. key length, …) - How is authentication handled (e.g. switched on?, signature verification, …) - Implementation errors

  9. GR01E - Electronic Commerce Overview Module 1 Technology: E2. Cryptography

  10. Dear Jean, I love you George This is $1000 Dollar (US!!)

  11. Cryptography Basics • Ciphers • Symmetric Key Algorithms • Public Key Algorithms • Message Digests • Digital Signatures • Trust networks

  12. Confidentiality (how can I make sure that an eavesdropper can not read my message) • Message integrity (how do I know that the message has not been modified on its travel?) • Authentication (how do I know that the message is from a particular person?)

  13. guvf zrffntr vf frperg __is __ss___ is s_____

  14. Relative frequency of letters in English text

  15. ROT13 algorithm (cipher): • abcdefghijklmnopqrstuvwxyz • nopqrstuvwxyzabcdefghijklm guvf zrffntr vf frperg __is __ss___ is s_____ __is _ess__e is se__e_ this _ess__e is se__et this message is secret

  16. Definitions (Encryption, Decryption, Plaintext, Ciphertext) Original Plaintext Plaintext Ciphertext Encryption Decryption Types of cipher: • Stream cipher • Each bit (or byte) is encrypted or decrypted individually • Simple substitution ciphers (ROT13, XOR) • Block cipher • A sequence of bits (or bytes) is used at each step in the encryption and decryption process (DES, AES)

  17. Symmetric Key Algorithms Key Key Original Plaintext Plaintext Ciphertext Encryption Decryption Public Key Cryptography Encryption Key Decryption Key Original Plaintext Plaintext Ciphertext Encryption Decryption

  18. Symmetric Key Algorithms General: • Substitution (ROT13, Cryptoquotes) • Transposition • XOR • One Time Pad Specific algorithms: • DES (data encryption standard, 56-bit key , Triple-DES) • IDEA (international data encryption algorithm, 128-bit key, patents) • RC2, RC4, RC5 (Ronald Rivest RSA, variable key length) • Rijndael (AES) (advanced encryption standard adapted in 2001) } most practical algorithms use a combination of these

  19. Rijndael: Iterated Block Cipher • 10/12/14 times applying the same round function • Round function: uniform and parallel, composed of 4 steps • Each step has its own particular function: • - ByteSub: nonlinearity • - ShiftRow: inter-column diffusion • - MixColumn: inter-byte diffusion within columns • - Round key addition

  20. What is an appropriate length for a key?

  21. Comparison of cryptographic algorithms

  22. Key distribution problem • Solutions: • Doubly padlocked box exchange • Diffie-Hellman key exchange • Public-key cryptography • (RSA, elliptic curve cryptography)

  23. The Diffie-Hellman key exchange was the first widely recognized • solution to the key exchange problem • Can only be used to exchange key. Symmetric key cryptographic • methods can be used to exchange secret messages • Fairly elaborate exchange of messages

  24. Public Key Cryptography A public key - private key pair are used, one for encryption and the other for decryption

  25. Public Key Cryptography (a la RSA) • A public key - private key pair are used, one for encryption and the other for decryption Example: • Let p=3, q=11 • n=pq=33 • e must be relatively prime to (p-1)(q-1)=20 • choose e = 7, then d = 7-1 mod 20 = 3 • Plaintext is 3,4,2 (m1=3, m2=4, m3=2) • c1=m1e mod n = 37 mod 33 = 9 • c2 = m2e mod n = 47 mod 33 = 15 • c3 = m3e mod n = 27 mod 33 = 29 • Ciphertext is 9,15,29 • m1=c1d mod n = 93 mod 33 = 3 • m2=c2d mod n = 153 mod 33 = 4 • m3=c3d mod n = 293 mod 33 = 2 • Plaintext is 3,4,2 Public Key: n - product of two primes, p and q (p and q are secret) e - relatively prime to (p-1)(q-1) Private Key: d - e-1mod ((p-1)(q-1)) Encrypting: c = me mod n Decrypting: m = cd mod n

  26. PGP: Pretty Good Privacy • Implementation of best available cryptographic algorithms for confidentiality and authentication and integration into a freely available general-purpose application • Package, source code, and documentation available on the web • Low-cost commercial version from Network Associates • Includes AES, 3DES, CAST, IDEA; RSA DSS, Diffie-Hellman; SHA1; key management, … Philip Zimmermann

  27. Message Digests & Hash function • A message digest is a one-way function which maps the information contained in a (small or large) file to a single large number, typically between 128 bits and 256 bits in length. • A good message digest function should have the following properties: • Every bit of the output is influenced by every bit of the input • Changing a single bit in the input results in every output bit having a 50% chance of changing • Given an input file, its corresponding digest, and the digest function, it is computationally infeasible to produce another input file which maps to the same digest

  28. http://ciips.ee.uwa.edu.au/~morris/Year2/PLDS210/hash_tables.htmlhttp://ciips.ee.uwa.edu.au/~morris/Year2/PLDS210/hash_tables.html

  29. Message Digests (continued) • Standard encryption algorithm • e.g. use last block in cipher feedback mode • Provide good message digest code • Computationally more demanding than other specialized functions • MD5 • One widely used message digest algorithm from a series of algorithms developed by Ronald Rivest • Does not rely on a secrete key and is therefore not suitable as MAC without further provisions • HMAC • The Hashed Message Authentication Code uses a shared secret key in combination with a message digest function to produce a secret message authentication code • Since an attacker doesn’t know the secret, the attacker cannot produce a correct authentication code if they alter the message • Fast to calculate, can be used as digital signature. However, a shared secret key is used. • SHA-1 • Developed by the NSA for use with the Digital Signature Standard

  30. Operation of a message digest function to produce a message authentication code Message Digest Algorithm MAC Message Hash Secret Key Block Cipher Message Authentication Code

  31. RSA Digital Signature Originator Transmitted Message Recipient Message Message Hash Function Hash Function Message Signature Public Key Decrypt Digest Private Key Encrypt Expected Digest Actual Digest Signature If actual and expected match, the signature is verified

  32. Types of authentication • What you know (username and password) • What you have (token, smart card) • What you are (biometrics) • Where you are (location security)

  33. Digital Certificates • Need a system for pairing public keys to identification information • Certification authority (or trusted third party) issues a certificate which pairs identification information with a public key, signed with the certification authority’s private key • User must trust the certification authority, and have a valid copy of the certification authority’s public key

  34. Digital Certificates (continued) Certificate Authority’s Private Key Certificate Subject Identification Information Generate Digital Signature Subject Public Key Value Certification Authority Name Certification Authority’s Digital Signature

  35. Certification Paths • More than one Certification Authority will be required • If CAs trust one another, they can issue certificates for each other’s public keys • This leads to a recursively defined path from a user under one CA to a user under another CA

  36. Subject = Certification Authority C Subject Public Key Issuer = Certification Authority B Subject = Bob Certificate 2 Subject Public Key Issuer = Certification Authority C Certificate 3 Certification Paths (continued) Public Key user Root Public Key (Certification Authority A) Subject = Certification Authority B Subject Public Key Issuer = Certification Authority A Certificate 1 Public – Private Key Pair Bob

  37. X.509 Certificate Format Versions 1 and 2 Certificate Version (of certificate format) Certificate Serial Number Certificate Authority’s Private Key Signature Algorithm Identifier Issuer’s X.500 Name Validity Period Subject’s X.500 Name Generate Digital Signature Algorithm Identifier Subject’s Public Key Information Public Key Value Issuer Unique Identifier Not in Version 1 Subject Unique Identifier Certification Authority’s Digital Signature

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