Introduction to Cryptography

Due to the rapid growth of digital communication and electronic data exchange, information security has become a crucial issue in industry, business, and administration. Modern cryptography provides essential techniques for securing information and protecting data.In the first part, this book covers the key concepts of cryptography on an undergraduate level, from encryption and digital signatures to cryptographic protocols. Essential techniques are demonstrated in protocols for key exchange, user identification, electronic elections and digital cash. In the second part, more advanced topics are addressed, such as the bit security of one-way functions and computationally perfect pseudorandom bit generators. The security of cryptographic schemes is a central topic. Typical examples of provably secure encryption and signature schemes and their security proofs are given. Though particular attention is given to the mathematical foundations, no special background in mathematics is presumed. The necessary algebra, number theory and probability theory are included in the appendix. Each chapter closes with a collection of exercises.The second edition contains corrections, revisions and new material, including a complete description of the AES, an extended section on cryptographic hash functions, a new section on random oracle proofs, and a new section on public-key encryption schemes that are provably secure against adaptively-chosen-ciphertext attacks. 1. Introduction -- Roadmap The Book -- What Type Of Book Is This? Terminology -- Notation -- Primer On Networking -- Osi Reference Model -- Directory Service -- Replicated Services -- Packet Switching -- Network Components -- Destinations: Ultimate And Intermediate -- Address Structure -- Tempest -- Firewalls /security Gatesway -- Packet Filters -- Application Level Getaway -- Encrypted Tunnels -- Key Escrow For Law Enforcement -- Key Escrow For Careless Users -- Viruses, Worms, Trojan Horses -- Where Do They Come From? Spreading Pests From Machine To Machine -- Virus Checkers -- What Can We Do Today? Wish List For The Future -- The Military Model Of Security -- Mandatory (nondiscretionary) Access Controls -- Levels Of Security -- Mandatory Access Control Rules -- Covert Channels -- The Orange Book -- Legal Issues -- Patents -- Export Controls -- 2. Introduction To Cryptography -- What Is Cryptography? Computational Difficulty -- To Publish Or Not To Publish -- Secret Codes -- Breaking An Encryption Scheme -- Ciphertext Only -- Known Plaintext -- Chosen Plaintext -- Types Of Cryptographic Functions -- Secret Key Cryptography -- Security Uses Of Secret Key Cryptography -- Transmitting Over An Insecure Channel -- Secure Storage On Insecure Media -- Authentication -- Integrity Check -- Public Key Cryptography -- Security Uses Of Public Key Cryptography -- Transmitting Over An Insecure Channel -- Secure Storage On Insecure Media -- Authentication -- Digital Signatures -- Hash Algorithms -- Password Hashing -- Message Integrity -- Message Fingerprint -- Downline Load Security -- Digital Signature Efficiency -- Homework -- 3. Secret Key Cryptography -- Introduction -- Generic Block Encryption -- Data Encryption Standard (des) -- Des Overview -- The Permutations Of The Data -- Generating The Per- Round Keys -- A Des Round -- The Mangler Function -- Weak And Semi-weak Keys -- What's So Special About Des? -- International Data Encryption Algorithm (idea) -- Primitive Operations -- Key Expansion -- One Round -- Odd Round -- Even Round -- Inverse Keys For Decryption -- Does Idea Work? Using Secret Key Cryptography In Protocols -- Encrypting A Large Message -- Electronic Code Book (ecb) -- Cipher Block Chaining (cbc) -- Cbc Threat 1 Modifying Ciphertext Blocks -- Cbc Threat 2 Rearranging Ciphertext Blocks -- Output Feedback Mode (ofb) -- Cipher Feedback Mode (cfb) -- Generating Mic's -- Ensuring Privacy And Integrity Together -- Cbc With A Weak Cryptographic Checksum -- Cbc With A Cryptographic Hash -- Cbc Encryption And Cbc Residue With Related Keys -- Multiple Encryption Des -- How Many Encryptions? Encrypting Twice With The Same Key -- Encrypting Twice With Two Keys -- Triple Encryption -- Cbc Outside Vs Inside -- Homework -- 4. Hashes And Message Digests -- Introduction -- Nifty Things To Do With A Hash -- Authentication -- Computing An Mic With A Hash -- Encryption With A Message Digest -- Generating A One-time Pad -- Mixing In The Plaintext -- Using Secret Key For A Hash -- Unix Password Hash -- Hashing Large Messages -- Md2 -- Md2 Padding -- 2. Md2 Checksum Computation -- Md2 Final Pass -- Md4. Md4 Message Padding -- Overview Of Md4 Message Digest Computation -- Md4 Message Digest Pass 1 -- Md4 Message Digest Pass 2 -- Md4 Message Digest Pass 3 -- Md5 -- Md5 Message Padding -- Overview Of Md5 Message Digest Computation -- Md5 Message Digest Pass 1 -- Md5 Message Digest Pass 2 -- Md5 Message Digest Pass 3 -- Md5 Message Digest Pass 4 -- Shs -- Shs Message Padding -- Overview Of Shs Message Digest Computation -- Shs Operation On A 512-bit Block -- Homework -- 5. Public Key Algorithms -- Introduction -- Modular Arithmetic -- Modular Addition -- Modular Multiplication -- Modular Exponentitation -- Rsa -- Rsa Algorithm -- Why Does Rsa Work -- Why Is Rsa Secure? How Efficient Are The Rsa Operations? Exponentiating With Big Numbers -- Generating Rsa Keys -- Finding Big Primes P And Q -- Finding D And E -- Having A Small Constant E -- Optimizing Rsa Private Key Operations -- Arcane Rsa Threats -- Smooth Numbers -- The Cube Root Problem -- Public-key Cryptography Standard (pkcs) -- Encryption -- Signing -- Diffie- Hellman -- The Bucket Brigade Attack -- Diffie-hellman With Published Public Papers -- Encryption With Diffie-hellman -- El Gamal Signatures -- Diffie- Hellman Details Strong Primes -- Digital Signature Standard (dss) -- The Dss Algorithm -- Why Does The Verification Procedure Work? Why Is This Secure? Per-message Secret Number -- Zero Knowledge Proof Systems -- Zero Knowledge Signatures -- Homework Problems -- 6. Number Theory -- Introduction -- Modular Arithmetic -- Primes -- Euclid's Algorithm -- Finding Multiplicative Inverses In Modular Arithmetic -- Chinese Remainder Theorem -- Zn* -- Euler's Totient Function -- Euler's Theorem -- A Generalization On Euler's Theorem -- Homework Problems -- 7. Authentication Systems -- Password-based Authentication -- Off- Vs On-line Password Guessing -- Storing User Passwords -- Address-based Authentication -- Network Address Impersonation -- Cryptographic Authentication Protocols -- Who Is Being Authenticated? Passwords As Cryptographic Keys -- Eavesdropping And Server Database Reading -- Trusted Intermediaries -- Kdcs -- Certification Authorities (cas) -- Certificate Revocation -- Multiple Trusted Intermediaries -- Multiple Kdc Domains -- Multiple Ca Domains -- Session Key. Establishment -- Authorization -- Groups -- Hierarchial Groups -- Delegation -- Homework 8. Authentication Of People -- Passwords -- On-line Password Guessing -- Off-line Password Guessing -- How Big Should A Secret Be? Eavesdropping -- Passwords And Careless Users -- Using A Password In Multiple Places -- Requiring Frequent Password Changes -- A Login Trojan Horse To Capture Passwords -- Non-login Use Of Passwords -- Initial Password Distribution -- Authentication Tokens -- Physical Access -- Biometrics -- Homework -- 9. Security Handshake Pitfalls -- Login Only -- Shared Secret -- One-way Public Key -- Lamport's Hash -- Mutual Authentication -- Reflection Attack -- Password Guessing -- Public Keys -- Timestamps -- Integrity /encryption For Data -- Shared Secret -- Two-way Public Key Based Authentication -- One-way Public Key Based Authentication -- Lamport Hash -- Privacy And Integrity -- Meditated Authentication (with Kdc) -- Needham- Schroeder -- Expanded Needham-schroeder -- Otway-rees -- Bellovin-merritt -- Network Login And Password Guessing -- Nonce Types -- Picking Random Numbers -- X609 Problem -- Performance Considerations -- Authentication Protocol Checklist -- Homework -- 10. Kerberos V4 -- Introduction -- Tickets And Ticket-granting Tickets -- Configuration -- Logging Into The Network -- Obtaining A Session Key And Tgt -- Alice Asks To Talk To A Remote Node -- Replicated Kdc's -- Realms -- Interrealm Authentication -- Key Version Numbers -- Encryption For Privacy And Integrity -- Encryption For Integrity Only -- Network Layer Addresses In Tickets -- Message Formats -- Tickets -- Authenticators -- Credentials -- As_req -- Tgs_req -- As_rep And Tgs_rep -- Error Reply From Kdc -- Ap_req -- Ap_rep -- Encrypted Data (krb_prv) -- Integrity-checked Data (safe) -- Ap_err -- Homework -- 11. Kerberos V5 -- Asn -- Names -- Delegation Of Rights -- Ticket Lifetimes -- Renewable Tickets -- Postdated Tickets -- Key Versions -- Making Master Keys In Different Realms Different -- Optimizations -- Cryptographic Algorithms -- Integrity-only Algorithms -- Rsa-md5-des -- Des-mac -- Des-mac-k -- Rsa-md4-des -- Rsa-md4-des-k -- Encryption For Privacy And Integrity -- Hierarchy Of Realms -- Evading Password-guessing Attacks -- Key Inside Authenticator -- Double Tgt Authentication -- Kdc Database -- Kerberos V5 Messages -- Authenticator -- Ticket -- As_req -- Tgs_req -- As_rep -- Tgs_rep -- Ap_req -- Ap-rep -- Krb_safe -- Krb_priv -- Krb_cred -- Krb_error -- Homework -- 12. Electronic Mail Security -- Distribution Lists -- Store And Forward -- Security Services For Electronic Mail -- Establishing Keys -- Establishing Public Keys -- Establishing Secret Keys -- Privacy -- End-to-end Privacy -- Privacy With Distribution List Exploders -- Authentication Of The Source -- Source Authentication Based On Public Key Technology -- Source Authentication Based On Secret Keys -- Source Authentication With Distribution Lists -- Message Integrity -- Message Integrity Without Source Authentication -- Non-repudiation -- Non-repudiation Based On Public Key Technology -- Plausible Deniability Based On Public Key Technology -- Non-repudiation With Secret Keys -- Proof Of Submission -- Proof Of Delivery -- Message Flow Confidentiality -- Anonymity -- Containment -- Annoying Text Format Issues -- Disguising Data As Text -- Names And Addresses -- Old Messages -- Case 1: The Dishonest Buyer -- Case 2: The Solution Looking For A Problem -- Homework -- 13. Privacy Enhanced Mail (pem) -- Introduction -- Structure Of A Pem Message -- Establishing Keys -- Some Pem History -- Certificate Hierarchy -- Certificate Revocation Lists (crls) -- X 509. Certificates And Crls -- Reformatting Data To Get Through Mailers -- General Structure Of A Pem Message -- Encryption -- Source Authentication And Integrity Protection -- Multiple Recipients -- Bracketing Pem Messages -- Remote Distribution List Exploders -- Remote Exploding Using Public Keys -- Remote Exploding Using Secret Keys -- Mixing Key Types -- Forwarding And Enclosures -- Forwarding A Message -- Canonicalization -- Unprotected Information -- Message Formats -- Encrypted, Public Key Variant -- Encrypted, Secret Key Variant -- Mic-only Or Mic-clear, Public Variant Key -- Mic-only Or Mic-clear, Secret Variant Key -- Crl-retrieval-request -- Crl -- Des-cbc As Mic Doesn't Work -- Homework -- 14. Pgp (pretty Good Privacy) -- Introduction -- Overview -- Key Distribution -- Efficient Encoding -- Certificate And Key Revocation -- Signature Types -- Your Private Key -- Key Rings -- Anomalies -- File Name -- People Names -- Object Formats -- Message Formats -- Primitive Object Formats -- 15. X400 -- Overview Of X400 -- Security Functions Possible With X400 -- Structure Of X400 Message -- Per-message Security Fields -- Per-recipient Security Fields -- Security Fields In The Token -- Unencrypted -- Part Of. The Token -- Encrypted -- Part Of. The Token -- Fields For Probe Messages -- Fields For Proof Of Delivery -- Fields For Proof Of Submission -- Security Fields For X -- 16. A Comparison Of Pem, Pgp, And X400 -- Introduction -- Certification Hierarchy -- Certificate Distribution -- Encryption -- Encoding Of Transmitted Messages -- Cryptographic Algorithms Supported -- Recipients With Multiple Keys -- Mail-intermediary-provided Functions -- 17. More Security Systems -- Netware V3 -- Netware V4 -- Netware's Gillou-quisquater Authentication Scheme -- Kryptoknight -- Kryptoknight Tickets -- Authenticators -- Nonces Vs -- Timestamps -- Data Encryption -- Snmp -- Dass /spx -- Dass Certification Hierarchy -- Obtaining The User's Private Key -- Dass Authentication Handshake -- Dass Authenticators -- Dadd Delegation -- Saving Bits -- Lotus Notes Security -- Id Files -- Coping With Export Controls -- Certificates For Flat Names -- Certificates For Hierarchical Names -- Lotus Notes Authentication -- Authentication Long-term Secret -- Mail -- Certification Revocation -- Dce Security -- Microsoft Security -- Network Denial Of Service -- Robust Broadcast -- Robust Packet Delivery -- Clipper -- Key Escrow -- Homework. Charlie Kaufman, Radia Perlman, Mike Speciner. Includes Bibliographical References (p. 471-479) And Indexs. Getting started; why security?; picking a security policy; strategies for a secure network; the ethics of computer security; warning; an overview of TCP/IP; the different layers; routers and routing protocols; the domain name system; standard services; RPC-based protocols; file transfer protocols; the "r" commands; information services; the X11 system; patterns of trust; building your own firewall; firewall gateways; firewall philosophy; situating firewalls; packet-filtering gateways; applicatio-level gateways; circuit-level gateways; supporting inbound services; tunnels good and bad; joint ventures; what firewalls can't do; how to build and application-level gateway; policy; hardware configuration options; initial installation; gateway tools; installing services; protecting the protectors; gateway administration; safety analysis-why our setup is secure and fail-safe; performance; the TIS firewall toolkit; evaluating firewalls; living without a firewalls; authentication; user authentication; host-to-host authentication; gateway tools; proxylib; syslog; watching the network: tcpdump and friends; adding logging to standard daemons; traps, lures, and honey pots; what to log; dummy accounts; tracing the connection; the hacker's workbench; introduction; discovery; probing hosts; connection tools; routing games; network monitors; metastasis; tiger teams; further reading;; a look back; classes of attacks; stealing passwords; social engineering; bugs and backdoors; authentication failures; information leakage; denial-of-service; an evening with berferd; the day after; the jail; tracing berferd; berferd comes home; where the wild things are: a look at the logs; a year of hacking; proxy use; attack sources; noise on the line; odds and ends; legal considerations; computer crime statutes; log files as evidence; is monitoring legal?; tort liability considerations; secure communications over insecure networks; an introduction to cryptography; the kerberos authentication system; link-level encryption; network-and transport-level encryption; application-level encryption; where do we go from here?; useful free stuff; building firewalls; network management and monitoring tools; auditing packages; cryptographic software; information sources; TCP and UDP ports; fixed ports; mbone usage; recommendations to vendors; everyone; hosts; routers; protocols; firewalls; bibliography; index

"This book provides an excellent overview of how encryption is used, its strengths and weaknesses, and what to look for when building or choosing real-world solutions. This is a must-have book for anyone considering the deployment of an important system relying on modern cryptography."

- Marcus J. Ranum Chief Scientist, V-ONE Corporation

Here, in one comprehensive, soup-to-nuts book, is the solution for Internet security: modern-day cryptography. Written by a security expert with a wealth of practical experience, this book covers network and Internet security in terms that are easy to understand, using proven technology, systems, and solutions. From the client workstation to the Web host to the e-mail server, every aspect of this important topic is examined and explained. The once-daunting subject of cryptography is demystified and applied to today's security challenges. Topics include:

• Essentials of cryptography
• Networking and Internet fundamentals
• Encryption building blocks
• Virtual private networks
• Legal considerations

• Setting realistic security objectives
• Secured electronic mail
• World Wide Web transaction security
• Internet Firewalls

This book is written for people who want to move data safely across the Internet and protect corporate resources from unauthorized access. Using real-life case studies, examples, and commercially available software products, cryptography is presented as a practical solution to specific, everyday security challenges.

An Introduction to Cryptography......Page 1 How to use this guide......Page 5 Technical support......Page 6 Non-Technical and beginning technical books......Page 7 Advanced books......Page 8 Table of Contents......Page 9 What is cryptography?......Page 11 How does cryptography work?......Page 12 Caesar’s Cipher......Page 13 Public key cryptography......Page 14 How PGP works......Page 16 Keys......Page 17 Digital signatures......Page 18 Hash functions......Page 19 Digital certificates......Page 21 Checking validity......Page 23 Trust models......Page 24 Hierarchical Trust......Page 25 Levels of trust in PGP......Page 26 What is a passphrase?......Page 27 Technical details......Page 28 Why I wrote PGP......Page 29 The PGP symmetric algorithms......Page 33 About the random numbers used as session keys......Page 35 About the message digest......Page 36 How to protect public keys from tampering......Page 37 How does PGP keep track of which keys are valid?......Page 40 How to protect private keys from disclosure......Page 42 Beware of snake oil......Page 43 Compromised passphrase and private key......Page 48 Not Quite Deleted Files......Page 49 Viruses and Trojan horses......Page 50 Swap files or virtual memory......Page 51 Protecting against bogus timestamps......Page 52 Exposure on multi-user systems......Page 53 Cryptanalysis......Page 54 Glossary......Page 57 Elgamal 15......Page 77 public key tampering 49......Page 78 Zimmermann, Phil 29......Page 79 Telecommunication has never been perfectly secure, as the Cold War culture of wiretaps and international spying taught us. Yet many of us still take our privacy for granted, even as we become more reliant than ever on telephones, computer networks, and electronic transactions of all kinds. So many of our relationships now use telecommunication as the primary mode of communication that the security of these transactions has become a source of wide public concern and debate. Whitfield Diffie and Susan Landau argue that if we are to retain the privacy that characterized face-to-face relationships in the past, we must build the means of protecting that privacy into our communication systems. Diffie and Landau examine the national-security, law-enforcement, commercial, and civil-liberties issues. They discuss privacy's social function, how it underlies a democratic society, and what happens when it is lost. They also explore how intelligence and law-enforcement organizations work, how they intercept communications, and how they use what they intercept. Avtor na lahko razumljiv način predstavlja kriptografijo kot sodobno in praktično metodo za zaščito interneta in omrežja. Knjiga je namenjena ljudem, ki ne vedo veliko o kriptografiji, a se pri svojem delu s poslovnimi podatki srečujejo z vprašanji njihovega varnega prenosa oziroma pošiljanja preko interneta, ko se morajo odločiti za določeno obliko kriptografske zaščite. Učinkovita uporaba kripto sistemov zahteva celovito razumevanje ciljev zaščite (npr. lokacije, transakcije, tajnosti sporočila) in njihove odvisnosti od sistemskih značilnosti. Knjiga ponuja odličen pregled uporabe enkripcije, njenih prednosti in slabosti, ter nove kriptografske proizvode in tehnologije, ki jih razvijajo posebej za aplikacije v internetu