Cryptography A Brief History Prasenjeet Dutta Cybernet Software Systems Inc. [email_address]
Presented at <ul><li>SRM College Chennai 2002 </li></ul>
In Today’s Session <ul><li>Part I The Ciphers </li></ul><ul><li>Part II The Politics </li></ul><ul><li>Part III Security a...
Basic Definitions <ul><li>Cryptography :  The Science of creating coded messages </li></ul><ul><li>Cryptanalysis :  The Ar...
Part I The Ciphers ◄  contents
Early History: Caesar Cipher <ul><li>Classically attributed to Julius Caesar </li></ul><ul><li>Simple “Shift By Three to t...
Transposition Ciphers <ul><li>Message Written in a Rectangular Block </li></ul><ul><li>Letters transposed in Pre-arranged ...
Vigenère Cipher <ul><li>Attributed to French mathematician Blaise de Vigenère, 1585 </li></ul><ul><li>Generalization of th...
One Time Pad (“Vernam Ciphers”) <ul><li>Special Case of the Vigenère Cipher </li></ul><ul><li>Plaintext length == Key leng...
WWII: The Enigma <ul><li>Mechanical Device: Gears/Plugs </li></ul><ul><li>Essentially a complex polyalphabetic cipher </li...
A Taxonomy of Ciphers <ul><li>Substitution Ciphers : The Ciphertext is formed by mathematically transforming the Plaintext...
Substitution Ciphers <ul><li>Monoalphabetic : only one sort of substitution is used, e.g. Caesar </li></ul><ul><li>Polyalp...
Substitution Ciphers, contd. <ul><li>Stream Cipher : generates a keystream and combines with plaintext to form ciphertext,...
Symmetric Ciphers <ul><li>Used for most heavy-duty encryption today </li></ul><ul><li>DES, Blowfish, Twofish, Rijndael… </...
The Key Distribution Problem <ul><li>Throughout history, ciphers were symmetric </li></ul><ul><li>Symmetric Ciphers share ...
Enter Public Key Cryptography <ul><li>Known to British and American Intelligence since the 1960s as “non-secret encryption...
R, S and A <ul><li>First Practical of a Diffie/Hellman Cryptosystem </li></ul><ul><li>Rivest, Shamir, Adelman 1978 </li></...
The RSA Algorithm <ul><li>Choose two primes p and q.  </li></ul><ul><li>Compute n = pq and s = (p-1)(q-1).  </li></ul><ul>...
RSA for Encryption <ul><li>Let p=7 and q=17.  </li></ul><ul><li>Thus n = pq = 119.  </li></ul><ul><li>Thus s = (p-1)(q-1) ...
RSA For Signing <ul><li>Using the same parameters as before, we will encrypt our plaintext (19) using our  private key . T...
PK vs. Symmetric Ciphers <ul><li>Symmetric Algorithms not obsolete </li></ul><ul><li>PK Ciphers far too slow </li></ul><ul...
Hashes and Steganography <ul><li>Hashes Verify Message Integrity </li></ul><ul><ul><li>Creates a fixed size output from va...
Part II The Politics ◄  contents
The Politics of Crypto <ul><li>Cryptography doesn’t occur in a vacuum </li></ul><ul><li>Crypto exists because bad guys exi...
Indian Law <ul><li>Import not restricted </li></ul><ul><ul><li>License may be required </li></ul></ul><ul><li>The IT Act 1...
US Cryptographic Law <ul><li>US prohibits export of certain “grades” of cryptographic products </li></ul><ul><ul><li>Thoug...
US Laws, contd. <ul><li>Allowed (2002 Rules): </li></ul><ul><ul><li>Nearly all Symmetric Algorithms </li></ul></ul><ul><ul...
Part III Security and Privacy ◄  contents
The Crypto Wars <ul><li>Daniel Bernstein waged a legal battle to declare the US Crypto Export Regulations illegal </li></u...
The Bigger Picture <ul><li>Cryptography is one step towards achieving a secure system, or our privacy </li></ul><ul><li>By...
The Black Hats Strike Back <ul><li>BonziBuddy, Kazaa and Nimda </li></ul><ul><ul><li>Threats for a new generation </li></u...
Pretty Bad Privacy <ul><li>“In God we trust. All others we monitor.” </li></ul><ul><ul><li>Tongue-in-cheek NSA motto </li>...
And it gets worse <ul><li>With strong crypto proliferating, NSA stated policy is to now go “beyond crypto” </li></ul><ul><...
That Said… <ul><li>…crypto is not totally useless </li></ul><ul><li>Good crypto is good enough to stop industrial espionag...
Improving Computer Security <ul><li>Become Security Aware </li></ul><ul><ul><li>Security is a Process </li></ul></ul><ul><...
Thanks for Listening! <ul><li>Questions? </li></ul><ul><li>◄  contents </li></ul>
Further Exploration <ul><li>Light Reading </li></ul><ul><ul><li>The Code Book , Simon Singh </li></ul></ul><ul><li>Introdu...
On the Internet <ul><li>sci.crypt FAQ </li></ul><ul><ul><li>http://www.faqs.org/faqs/by-newsgroup/sci/sci.crypt.html </li>...
The End
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Cryptography - A Brief History

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An introductory 2002 tour of cryptography for beginners, covering the basics of the technology and the social context cryptography operates in.

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  • Cryptography - A Brief History

    1. 1. Cryptography A Brief History Prasenjeet Dutta Cybernet Software Systems Inc. [email_address]
    2. 2. Presented at <ul><li>SRM College Chennai 2002 </li></ul>
    3. 3. In Today’s Session <ul><li>Part I The Ciphers </li></ul><ul><li>Part II The Politics </li></ul><ul><li>Part III Security and Privacy </li></ul><ul><li>Part IV Questions </li></ul>
    4. 4. Basic Definitions <ul><li>Cryptography : The Science of creating coded messages </li></ul><ul><li>Cryptanalysis : The Art of breaking coded messages </li></ul><ul><li>Cleartext : the original message </li></ul><ul><li>Ciphertext : the encoded message </li></ul><ul><li>Key : Input to the cryptographic algorithm </li></ul><ul><li>Passphrase : User input from which the key is usually derived </li></ul>
    5. 5. Part I The Ciphers ◄ contents
    6. 6. Early History: Caesar Cipher <ul><li>Classically attributed to Julius Caesar </li></ul><ul><li>Simple “Shift By Three to the Right” Rule </li></ul><ul><ul><li>“ATTACK” would become “DWWDFN” </li></ul></ul><ul><li>Easily Breakable if you knew the Rule </li></ul><ul><li>Today, easily breakable otherwise as well </li></ul><ul><li>Demo </li></ul>
    7. 7. Transposition Ciphers <ul><li>Message Written in a Rectangular Block </li></ul><ul><li>Letters transposed in Pre-arranged order </li></ul><ul><li>ATTACK CORSICA AT DAWN becomes </li></ul><ul><ul><li>A T T A C AKID TCCA TOAW ARAN CSTX </li></ul></ul><ul><ul><li>K C O R S </li></ul></ul><ul><ul><li>I C A A T </li></ul></ul><ul><ul><li>D A W N X </li></ul></ul><ul><li>Demo </li></ul>
    8. 8. Vigenère Cipher <ul><li>Attributed to French mathematician Blaise de Vigenère, 1585 </li></ul><ul><li>Generalization of the Caesar Cipher </li></ul><ul><li>Bidirectional n-Shift cipher </li></ul><ul><li>Considered secure until 1863 </li></ul><ul><ul><li>The Kasiski/Kerchoff method of Frequency Analysis and the “Index of Coincidence” </li></ul></ul><ul><li>Demo </li></ul>
    9. 9. One Time Pad (“Vernam Ciphers”) <ul><li>Special Case of the Vigenère Cipher </li></ul><ul><li>Plaintext length == Key length </li></ul><ul><li>Key is assumed to be random </li></ul><ul><li>Proven to be mathematically secure against all attacks </li></ul><ul><li>Randomness not easy to generate </li></ul><ul><li>Non-randomness of key makes algorithm breakable </li></ul><ul><li>Has been used for ultra-sensitive telephonic hotlines </li></ul>
    10. 10. WWII: The Enigma <ul><li>Mechanical Device: Gears/Plugs </li></ul><ul><li>Essentially a complex polyalphabetic cipher </li></ul><ul><li>Key Transport major issue </li></ul><ul><li>GCHQ cracked it </li></ul><ul><ul><li>Turning point in the war </li></ul></ul><ul><li>Demo </li></ul>
    11. 11. A Taxonomy of Ciphers <ul><li>Substitution Ciphers : The Ciphertext is formed by mathematically transforming the Plaintext </li></ul><ul><ul><li>Most commonly Used </li></ul></ul><ul><li>Transposition Ciphers : The Ciphertext is formed by re-arranging the Plaintext </li></ul><ul><ul><li>Considered Primitive </li></ul></ul><ul><li>Concealment Ciphers : The Plaintext is “hidden” away from ordinary view </li></ul>
    12. 12. Substitution Ciphers <ul><li>Monoalphabetic : only one sort of substitution is used, e.g. Caesar </li></ul><ul><li>Polyalphabetic : more than one substitution, e.g. Vigenère, Enigma </li></ul><ul><li>Block Cipher : Operates on discrete blocks of plaintext, outputs discrete blocks of ciphertext, e.g. DES, Blowfish, Rijndael </li></ul><ul><ul><li>Ideal for offline encryption of large blocks of data at a time </li></ul></ul>
    13. 13. Substitution Ciphers, contd. <ul><li>Stream Cipher : generates a keystream and combines with plaintext to form ciphertext, e.g. RSA’s RC4 </li></ul><ul><ul><li>Suitable for online encryption of smaller chunks of data, e.g. Encrypting Voice Comms </li></ul></ul><ul><ul><li>Approximates a One Time Pad when used this way </li></ul></ul><ul><ul><li>Much faster than block ciphers for online work </li></ul></ul><ul><ul><li>Block ciphers can also emulate stream ciphers, though slowly </li></ul></ul>
    14. 14. Symmetric Ciphers <ul><li>Used for most heavy-duty encryption today </li></ul><ul><li>DES, Blowfish, Twofish, Rijndael… </li></ul><ul><li>One Common Key for Encryption and Decryption </li></ul><ul><li>Decryption is the mathematical inverse of encryption, i.e.: </li></ul><ul><ul><li>F (plaintext, key) = ciphertext </li></ul></ul><ul><ul><li>F (ciphertext, key) = plaintext </li></ul></ul>
    15. 15. The Key Distribution Problem <ul><li>Throughout history, ciphers were symmetric </li></ul><ul><li>Symmetric Ciphers share encryption and decryption keys </li></ul><ul><li>Key Dist presents practical problems </li></ul><ul><li>Prone to Man-in-the-middle attacks </li></ul><ul><li>This situation lasted until 1976 </li></ul>
    16. 16. Enter Public Key Cryptography <ul><li>Known to British and American Intelligence since the 1960s as “non-secret encryption” </li></ul><ul><li>Non-classified invention would take 15 more years </li></ul><ul><li>Practical only with large scale computer resources </li></ul><ul><li>Concept and Key-Exchange technique proposed by Diffie/Hellman, 1976 </li></ul><ul><ul><li>No Cryptosystem implementation </li></ul></ul>
    17. 17. R, S and A <ul><li>First Practical of a Diffie/Hellman Cryptosystem </li></ul><ul><li>Rivest, Shamir, Adelman 1978 </li></ul><ul><li>System allowed Encryption/Decryption, Key Exchange and Message Signing </li></ul><ul><li>Other PK algorithms today: </li></ul><ul><ul><li>Diffie/Hellman, ElGamal, DSA </li></ul></ul><ul><li>Even today, RSA probably most versatile </li></ul>
    18. 18. The RSA Algorithm <ul><li>Choose two primes p and q. </li></ul><ul><li>Compute n = pq and s = (p-1)(q-1). </li></ul><ul><li>Choose e such that e is relatively prime to s and e < s. Find d such that de = 1 mod s and d < s. </li></ul><ul><li>The private key KR = {d, n}. </li></ul><ul><li>The public key KU = {e, n}. </li></ul><ul><li>Encryption is: C = m e (mod n). </li></ul><ul><li>Decryption is: M = C d (mod n). </li></ul>
    19. 19. RSA for Encryption <ul><li>Let p=7 and q=17. </li></ul><ul><li>Thus n = pq = 119. </li></ul><ul><li>Thus s = (p-1)(q-1) = 96. </li></ul><ul><li>We choose e = 5. </li></ul><ul><li>We determine ‘d’ to be 77, since 77x5 = 385 = 4x96 + 1, that is, de=1 mod s and d < s </li></ul><ul><li>Encryption (for a plaintext M = 19). </li></ul><ul><li>(19^5) % 119 = 66 </li></ul><ul><li>Decryption (for a ciphertext M = 19). </li></ul><ul><li>(66^77) % 119 = 19 </li></ul>
    20. 20. RSA For Signing <ul><li>Using the same parameters as before, we will encrypt our plaintext (19) using our private key . This is equivalent to “signing” </li></ul><ul><li>Signing (for a plaintext M = 19) </li></ul><ul><li>(19^77) % 119 = 66. </li></ul><ul><li>The corresponding decryption using our public key is called “verification.” </li></ul><ul><li>Decryption (for a signed text S = 66) </li></ul><ul><li>(66^5) % 119 = 19. </li></ul>
    21. 21. PK vs. Symmetric Ciphers <ul><li>Symmetric Algorithms not obsolete </li></ul><ul><li>PK Ciphers far too slow </li></ul><ul><li>PK ciphers better suited to transporting symmetrical keys or message digests than general purpose encryption. </li></ul><ul><li>PK Ciphers require very large keys to attain decent security </li></ul><ul><ul><li>a 128 bit RSA key is very weak compared to a 128 bit Blowfish key. </li></ul></ul><ul><li>PK Algorithms tend to be simple mathematically, depending on the NP-hardness of their algorithms for security </li></ul><ul><li>Symmetric algorithms tend to be convoluted because of multiple steps, many of them non-linear. </li></ul>
    22. 22. Hashes and Steganography <ul><li>Hashes Verify Message Integrity </li></ul><ul><ul><li>Creates a fixed size output from variable-length input using a one-way series of transforms </li></ul></ul><ul><ul><li>MD5 and SHA-1 are the most used algorithms </li></ul></ul><ul><li>Steganography attempts to hide “real” messages within a larger, “innocent” message </li></ul><ul><ul><li>Often used to disguise the fact that any message is being transmitted at all </li></ul></ul><ul><ul><li>Demo </li></ul></ul>
    23. 23. Part II The Politics ◄ contents
    24. 24. The Politics of Crypto <ul><li>Cryptography doesn’t occur in a vacuum </li></ul><ul><li>Crypto exists because bad guys exist </li></ul><ul><li>Crypto products are munitions according to the US BXA </li></ul><ul><ul><li>Illegal Export is a federal felony </li></ul></ul><ul><ul><li>After 9/11, can be a terrorist-abetment offence </li></ul></ul><ul><li>If you work on crypto, know your laws! </li></ul>
    25. 25. Indian Law <ul><li>Import not restricted </li></ul><ul><ul><li>License may be required </li></ul></ul><ul><li>The IT Act 1999 requires mandatory key surrender if required for national security </li></ul>
    26. 26. US Cryptographic Law <ul><li>US prohibits export of certain “grades” of cryptographic products </li></ul><ul><ul><li>Though they are very easily downloadable over the Net </li></ul></ul><ul><li>Most cryptographic functions in US software used to be crippled badly before export </li></ul><ul><ul><li>MSIE 4, 5 with “56 bit” security </li></ul></ul><ul><ul><li>Lotus Notes with “64-24 bit” security </li></ul></ul><ul><li>Today, general export (except to the Terrorist “T-7” nations) is permitted </li></ul>
    27. 27. US Laws, contd. <ul><li>Allowed (2002 Rules): </li></ul><ul><ul><li>Nearly all Symmetric Algorithms </li></ul></ul><ul><ul><ul><li>Lengths above 64 bits require mandatory notification </li></ul></ul></ul><ul><ul><li>PK Ciphers up to 512 bits </li></ul></ul><ul><ul><li>Elliptic Curve Ciphers up to 112 bits </li></ul></ul><ul><li>Why is US Law so Important? </li></ul><ul><ul><li>Largest exporter of Software </li></ul></ul><ul><ul><li>Most European Countries have a problem with this </li></ul></ul><ul><ul><li>Germany currently funding GPG </li></ul></ul>
    28. 28. Part III Security and Privacy ◄ contents
    29. 29. The Crypto Wars <ul><li>Daniel Bernstein waged a legal battle to declare the US Crypto Export Regulations illegal </li></ul><ul><li>Philip Zimmerman wrote PGP to take crypto to the masses </li></ul><ul><li>The hope was that good, ubiquitous crypto would make computing secure for everyone </li></ul><ul><li>Eventually, the Crypto Regulations crumbled </li></ul><ul><li>Is secure computing there yet? </li></ul>
    30. 30. The Bigger Picture <ul><li>Cryptography is one step towards achieving a secure system, or our privacy </li></ul><ul><li>By itself, it guarantees nothing </li></ul><ul><li>Security is a Process </li></ul><ul><ul><li>No silver bullets </li></ul></ul><ul><ul><li>Not even cryptography </li></ul></ul><ul><ul><li>All crypto is breakable, given enough time and computer resources </li></ul></ul>
    31. 31. The Black Hats Strike Back <ul><li>BonziBuddy, Kazaa and Nimda </li></ul><ul><ul><li>Threats for a new generation </li></ul></ul><ul><li>Crypto too hard to use for common users </li></ul><ul><ul><li>Despite S/MIME, secure email has not taken off </li></ul></ul><ul><li>Palladium (MS) and TCPA (Intel) now aim to take crypto into hardware </li></ul><ul><ul><li>But not all the security infrastructure in the world will help protect non-security-minded users </li></ul></ul>
    32. 32. Pretty Bad Privacy <ul><li>“In God we trust. All others we monitor.” </li></ul><ul><ul><li>Tongue-in-cheek NSA motto </li></ul></ul><ul><li>28 dishes </li></ul><ul><li>100k simultaneous calls </li></ul><ul><li>2 million messages/hr </li></ul><ul><li>17.5 billion messages/yr </li></ul><ul><li>And that’s just one station: Menwith Hill, UK </li></ul><ul><li>Plus satellite interceptors, undersea taps, etc </li></ul>
    33. 33. And it gets worse <ul><li>With strong crypto proliferating, NSA stated policy is to now go “beyond crypto” </li></ul><ul><ul><li>Keystroke Logging to capture keystrokes </li></ul></ul><ul><ul><li>Van Eck Phreaking to read characters from Electromagnetic Radiation from monitors </li></ul></ul><ul><ul><li>Spy Satellites can now spot 10cm 2 objects from orbit </li></ul></ul><ul><ul><li>Mandated ISP taps (Carnivore) </li></ul></ul><ul><ul><li>Social Engineering </li></ul></ul><ul><li>9/11 has added urgency </li></ul><ul><ul><li>Intelligence agencies must combine/pool databases </li></ul></ul><ul><ul><li>The goal is “Total Information Awareness” </li></ul></ul>
    34. 34. That Said… <ul><li>…crypto is not totally useless </li></ul><ul><li>Good crypto is good enough to stop industrial espionage, network snoopers and casual crackers/script kiddies </li></ul><ul><li>Crypto-enabled protocols are much more secure than vanilla FTP, Telnet or HTTP </li></ul>
    35. 35. Improving Computer Security <ul><li>Become Security Aware </li></ul><ul><ul><li>Security is a Process </li></ul></ul><ul><li>No Magic Bullets </li></ul><ul><ul><li>Windows, Linux, Trusted Solaris: all need work </li></ul></ul><ul><li>Encrypt Network Traffic: SSH, HTTPS, SFTP </li></ul><ul><li>Use IPSec and DNSSec if you can </li></ul><ul><li>Avoid Single Points of Failure </li></ul><ul><li>Audit ! </li></ul>
    36. 36. Thanks for Listening! <ul><li>Questions? </li></ul><ul><li>◄ contents </li></ul>
    37. 37. Further Exploration <ul><li>Light Reading </li></ul><ul><ul><li>The Code Book , Simon Singh </li></ul></ul><ul><li>Introduction </li></ul><ul><ul><li>Cryptography and Network Security , William Stallings </li></ul></ul><ul><li>Graduate Level </li></ul><ul><ul><li>Handbook of Applied Cryptography </li></ul></ul><ul><ul><ul><li>http://www.cacr.math.uwaterloo.ca/hac/ </li></ul></ul></ul>
    38. 38. On the Internet <ul><li>sci.crypt FAQ </li></ul><ul><ul><li>http://www.faqs.org/faqs/by-newsgroup/sci/sci.crypt.html </li></ul></ul><ul><li>Crypto Link Farm </li></ul><ul><ul><li>http://www.cs.auckland.ac.nz/~pgut001/links.html </li></ul></ul><ul><li>Crypto-Gram </li></ul><ul><ul><li>http://www.counterpane.com/crypto-gram.html </li></ul></ul>
    39. 39. The End
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