Download as PDF, PPTX
Uploaded bySam Bowne
Ch 12: Cryptography
This document summarizes cryptography concepts including symmetric and asymmetric encryption algorithms, hashing algorithms, and attacks on cryptosystems. Symmetric algorithms like AES and Blowfish use a single key for encryption and decryption while asymmetric algorithms like RSA and ECC use public/private key pairs. Hashing algorithms like SHA-1 produce a digest to ensure message integrity. Cryptanalysis studies breaking encryption while brute force involves testing all possible keys.
More Related Content
Ch 12: Cryptography
- 1. Hands-On Ethical Hacking andNetwork Defense 3 rd Edition Chapter 12 Cryptography Last modified 4-20-17
- 2. Objectives • Describe thehistory of cryptography • Describe symmetric and asymmetric cryptography algorithms • Explain public key infrastructure (PKI) • Describe possible attacks on cryptosystems • Compare hashing algorithms and how they ensure data integrity
- 3. Understanding Cryptography Basics • Cryptographyis the process of converting plaintext into ciphertext • Plaintext: readable text (also called cleartext) • Ciphertext: unreadable or encrypted text • Cryptography is used to hide information from unauthorized users • Decryption is the process of converting ciphertext back to plaintext
- 4. History of Cryptography •Substitution cipher • Replaces one letter with another letter based on a key • Example: Julius Caesar’s Cipher • Used a key value of 3 • ABCDEFGHIJKLMNOPQRSTUVWXYZ • DEFGHIJKLMNOPQRSTUVWXYZABC
- 5. ROT-13 • A Caesar cipher •Performing ROT-13 twice undoes it • Obfuscation, not Encryption • From Wikipedia
- 6. History of Cryptography (continued) •Cryptanalysis studies the process of breaking encryption algorithms • When a new encryption algorithm is developed, cryptanalysts study it and try to break it • Or prove that it is impractical to break it (taking much time and many resources)
- 7. Enigma • Used bythe Germans during World War II • Replaced letters as they were typed • Substitutions were computed using a key and a set of switches or rotors • Image from Wikipedia (link Ch 12a)
- 8. Steganography • The processof hiding data in plain view in pictures, graphics, or text • Example: changing colors slightly to encode individual bits in an image • The image on the left contains the image on the right hidden in it (link Ch 12c)
- 9. Algorithms • An algorithmis a mathematical function or program that works with a key • Security comes from • A strong algorithm—one that cannot be reversed without the key • A key that cannot be found or guessed
- 10. Keys (not in textbook) •A sequence of random bits • The range of allowable values is called a keyspace • The larger the keyspace, the more secure the key • 8-bit key has 28 = 256 values in keyspace • 24-bit key has 224 = 16 million values • 56-bit key has 256 = 7 x 1016 values • 128-bit key has 2128 = 3 x 1038 values
- 11. Brute Force (notin textbook) • In 1997 a 56-bit key was broken by brute force • Testing all possible 56-bit keys • Used 14,000 machines organized via the Internet • It took 3 months • See link Ch 12d
- 12. How Many BitsDo You Need? (not in textbook) • How many keys could all the computers on Earth test in a year? • Pentium 4 processor: 109 cycles per second • One year = 3 x 107 seconds • There are less than 1010 computers on Earth • One per person • 109 x 3 x 107 x 1010 = 3 x 1026 calculations • 128 bits should be enough (3 x 1038 values) • Unless computers get much faster, or someone breaks the algorithm
- 13. But if Moore’sLaw Continues (not in textbook) • Suppose computers double in speed every 2 years (link Ch 12zi) • 1000x faster every 20 years • 2010:1027 calcs/year 90 bits • 2030:1030 calcs/year 100 bits • 2050:1033 calcs/year 110 bits • 2070:1036 calcs/year 120 bits • 2090:1039 calcs/year 130 bits • 128 bits may not be enough (3 x 1038 values)
- 14. Symmetric Cryptography • Onekey encrypts and decrypts data • Cleartext with Key makes Ciphertext • Ciphertext with Key makes Cleartext Winning Lotto #s: aWDHOP#@-w9 aWDHOP#@-w9 Winning Lotto #s:
- 15. Symmetric Cryptography Algorithms • Symmetricalgorithms have one key that encrypts and decrypts data • Advantages • Symmetric algorithms are fast • They are difficult to break if a large key size is used • Only one key needed
- 16. Symmetric Cryptography Algorithms •Disadvantages • Symmetric keys must remain secret • Difficult to deliver keys (key distribution) • Symmetric algorithms don’t provide authenticity or nonrepudiation • You can’t know for sure who sent the message, since two people have the same key
- 17. Symmetric Cryptography Algorithms • Typesof symmetric algorithms • Stream ciphers • Operate on plaintext one bit at a time • Block ciphers • Operate on blocks of plaintext
- 18. DeCSS • Commercial DVDsare encoded with a 40- bit key • It’s simple to crack it by brute force • Three hackers did that in 1999 • See links Ch 12e, 12f • Legislation such as the DMCA made it illegal to publish the algorithm • See Illegal Prime Number (Link Ch 12g)
- 19. Data Encryption Standard(DES) • National Institute of Standards and Technology (NIST) • Wanted a means of protecting sensitive but unclassified data • Invited vendors in early 1970 to submit data encryption algorithms • IBM proposed Lucifer • A 128-bit encryption algorithm
- 20. Data Encryption Standard(DES) • The National Security Agency (NSA) reduced the key size from 128 bits to 64 bits and created DES • Only 56 bits of the key are actually used
- 21. Data Encryption Standard(DES) (continued) • In 1988, NSA thought the standard was at risk to be broken • In 1997, a DES key was broken in 3 months • In 1998, the EFF built a a computer system that cracked a DES key in 3 days • Link Ch 12h
- 22. Triple DES (3DES) •Triple Data Encryption System (3DES) • 3DES served as a quick fix to the vulnerabilities of DES • 3DES performs three DES encryptions • 256 times stronger than DES • More secure but slower to compute • See link Ch 12i
- 23. Advanced Encryption Standard(AES) • Became effective in 2002 as a standard • The process took 5 years • Block cipher that operates on 128-bit blocks of plaintext • Keys can be 128, 192, or 256 bits • Uses Rindjael algorithm • Link Ch 12j
- 24. International Data Encryption Algorithm(IDEA) • Block cipher that operates on 64-bit blocks of plaintext • It uses a 128-bit key • Developed by Xuejia Lai and James Massey • Designed to work more efficiently in computers used at home and in businesses • IDEA is free for noncommercial use • It is included in PGP encryption software
- 25. Blowfish • Block cipherthat operates on 64-bit blocks of plaintext • The key length can be as large as 448 bits • Developed by Bruce Schneier
- 26. RC4 • The mostwidely used stream cipher • Used in WEP and WPA (part of TKIP) • Also used in some versions of TLS • Link Ch 12zz1
- 27. • Weakness: RC4is biased--some byte sequences are more common than others • Can decrypt an HTTPS cookie in 75 hours • If RC4 is used • Can break WPA-TKIP within an hour
- 28. RC5 • Block cipherthat can operate on different block sizes: 32, 64, and 128 • The key size can reach 2048 bits • Created by Ronald L. Rivest in 1994 for RSA Data Security
- 29. Cracking RC5 • 56-bitand 64-bit key RC5s have already been cracked • The RC5-72 project is underway, trying to crack a 72-bit key • At the current rate, it will take 1000 years • Links Ch 12l, 12m
- 30.
- 31. What technique hidesthe existence of a message? A. Steganography B. Substitution Cipher C.Cryptanalysis D.Brute Force E. Algorithm
- 32. What process decryptsan encrypted message by finding mathematical problems in the technique? A. Enigma B. Substitution Cipher C.Cryptanalysis D.Brute Force E. Algorithm
- 33. What is theweakest encryption technique on the list? A. 3DES B. AES C.DES D.CSS (Content Scrambling System) E. Blowfish
- 34. Which encryption techniqueused a 56- bit key and was used by American businesses until it was cracked? A. 3DES B. AES C.DECSS D.DES E. Blowfish
- 35. Asymmetric Cryptography Algorithms •Use two keys that are mathematically related • Data encrypted with one key can be decrypted only with the other key • Another name for asymmetric key cryptography is public key cryptography • Public key: known by the public • Private key: known only by owner
- 36. Asymmetric Cryptography • Cleartextwith Public Key makes Ciphertext • Ciphertext with Private Key makes Cleartext Winning Lotto #s: aWDHOP#@-w9 aWDHOP#@-w9 Winning Lotto #s:
- 37. Asymmetric Cryptography • Providesmessage authenticity and nonrepudiation • Authenticity validates the sender of a message • Nonrepudiation means a user cannot deny sending a message
- 38. Asymmetric Cryptography • Asymmetricalgorithms are more scalable but slower than symmetric algorithms • Scalable: can adapt to larger networks • Each person needs only one key pair • Everyone can use the same public key to send you data • Each person signs messages with their own private key
- 39. RSA • Developed in1977 by Ronald L. Rivest, Adi Shamir, and Leonard M. Adleman • The algorithm is based on the difficulty of factoring large numbers • The Secure Socket Layer (SSL) protocol uses the RSA algorithm Ron Rivest
- 40. Diffie-Hellman • Developed byWhitfield Diffie and Martin Hellman • Does not provide encryption but is used for key exchange • Two parties agree on a key without ever sending it directly over the network • The numbers transmitted can be used to compute the key, but only by the parties holding secret private numbers • Prevents sniffing attacks Whitfield Diffie
- 41. Elliptic Curve Cryptosystems(ECC) • It is an efficient algorithm requiring few resources • Memory • Disk space • Bandwidth • ECC is used for encryption as well as digital signatures and key distribution
- 42. Elgamal • Public keyalgorithm used to • Encrypt data • Create digital signature • Exchange secret keys • Written by Taher Elgamal in 1985 • The algorithm uses discrete logarithm problems • Solving a discrete logarithm problem can take many years and require CPU-intensive operations
- 43. NSA & ECC •NSA apparently backdoor the random number generator • Goal: NOBUS (Nobody But Us) • Link Ch 12zw, 12zx, 12zy
- 44. • Link Ch12zz
- 45. NSA & QuantumComputing
- 46. NSA & QuantumComputing • NSS = National Security System • Link Ch 12zy
- 47. NSA & QuantumComputing • The public-key algorithms (RSA, Diffie- Hellman, ECDH, and ECDSA) are all vulnerable to attack by a sufficiently large quantum computer. • Quantum computing techniques are much less effective against symmetric algorithms than against widely used public key algorithms. • AES-256 and SHA-384 are believed to be safe from attack by a large quantum computer. • Link Ch 12zy
- 48. NSA & QuantumComputing • NSS should now use these key sizes: • Elliptic Curves: 384 bits • RSA & Diffie-Hellman: 3072 bits • Link Ch 12zy
- 49. • Since ahandful of primes are so widely reused, … • Breaking a single, common 1024-bit prime would allow NSA to passively decrypt connections to two-thirds of VPNs and a quarter of all SSH servers globally. • Breaking a second 1024-bit prime would allow passive eavesdropping on connections to nearly 20% of the top million HTTPS websites. • Link Ch 12zx (Oct, 2015)
- 50.
- 51. Digital Signature Standard(DSS) • Established by the NIST in 1991 • Ensures that digital signatures rather than written signatures can be verified • Federal government requirements • RSA and Digital Signature Algorithm (DSA) must be used for all digital signatures • Hashing algorithm must be used to ensure the integrity of the message • NIST required that the Secure Hash Algorithm (SHA) be used
- 52. Pretty Good Privacy(PGP) • Developed by Phil Zimmerman as a free e-mail encryption program • Zimmerman was almost arrested for his innovation • Back in the mid-1990s, any kind of “unbreakable” encryption was seen as a weapon and compared to selling arms to the enemy
- 53. Pretty Good Privacy(PGP) • PGP is a free public key encryption program • It uses certificates similar to those in public key infrastructure (PKI) • PGP does not use a centralized CA • Verification of a certificate is not as efficient as PKI
- 54. Pretty Good Privacy(PGP) (continued) • Algorithms supported by PGP • IDEA • RSA • DSA • Message Digest 5 (MD5) • SHA-1
- 55. Secure Multipurpose InternetMail Extension (S/MIME) • Is another public key encryption standard used to encrypt and digitally sign e-mail • Can encrypt e-mail messages containing attachments • Can use PKI certificates for authentication • S/MIME version 2 defined in RFC 2311 • S/MIME version 3 defined in RFC 2633
- 56. Privacy-Enhanced Mail (PEM) •Internet standard that is compatible with both symmetric and asymmetric methods of encryption • Can use the X.509 certificate standards and encrypt messages with DES • Not used as much today • MIME Object Security Services (MOSS) is a newer implementation of PEM
- 57. Hashing Algorithms • Takea variable-length message and produce a fixed-length value called a message digest • A hash value is equivalent to a fingerprint of the message • If the message is changed later, the hash value changes
- 58. Collisions • If twodifferent messages produce the same hash value, it results in a collision • A good hashing algorithm must be collision-free • MD5 has known collisions • It was never approved by NIST for any purpose
- 59. SHA-1 • SHA-1 isone of the most popular hashing algorithms • No known collisions as of 2015 • But several attacks have been developed showing that SHA-1 is weaker than it should be • See link Ch 12q
- 60. AOL = Bad Microsoft= Good Why?
- 61. • Researchers believethat a SHA-1 collision could be found in 2015 for $75,000 to $120,000 • Link Ch 12zw (Oct, 2015) • But none has been found, as of 1-11-17
- 62. Browsers Deprecating SHA-1 •Link Ch 12zr
- 63. • Link Ch12zq
- 64. Colleges Tested in2014 • Link Ch 12zs
- 65. Banks Tested in2014 • Link Ch 12zt
- 66. Digital Signatures • Ahash value ensures that the message was not altered in transit (integrity) • Asymmetric encryption assures authenticity and nonrepudiation
- 67. Symmetric Algorithms (Private-key) Name Keysize Notes DES 56 bits Insecure 3DES 168 bits Being replaced by AES AES 128,192, or 256 US Govt classified info IDEA 128 bits Used in PGP, very secure Blowfish 32 to 448 Public domain RC5 Up to 2040 Secure for 72-bits or more
- 68. Asymmetric Algorithms (Public-key) Name Notes Diffie-HellmanKey exchg, not encryption RSA Secure, used by SSL ECC Efficient newer technique Elgamal Used in GPG and PGP
- 69. Hashing Algorithms Name Notes MD2Written for 8-bit machines, no longer secure MD4 No longer secure MD5 Security is questionable now SHA-1 The successor to MD5, Used in: TLS, SSL, PGP, SSH, S/MIME, IPsec No longer completely secure SHA-2 Not yet broken NIST is now developing a new algorithm to replace SHA.
- 70.
- 71. If Alice wantsto send a private message to Bob using asymmetric cryptography, what key does she use to encrypt the message? A. Alice’s private key B. Alice’s public key C.Bob’s private key D.Bob’s public key E. None of the above
- 72. If Alice wantsto sign a contract, what key does she use to encrypt the hash value? A. Alice’s private key B. Alice’s public key C.Bob’s private key D.Bob’s public key E. None of the above
- 73. What process isperformed without a key? A. Asymmetric cryptography B. Symmetric cryptography C.Hashing D.More than one of the above E. None of the above
- 74. Public Key Infrastructure(PKI) • Not an algorithm • A structure that consists of programs, protocols, and security protocols • Uses public key cryptography • Enables secure data transmission over the Internet
- 75. PKI Components • Certificate:a digital document that verifies the identity of an entity • Contains a unique serial number and must follow the X.509 standard
- 76. PKI Components • Publickeys are issued by a certification authority (CA) • A certificate that the CA issues to a company binds a public key to the recipient’s private key
- 77. Certificate Expiration andRenewal • A period of validity is assigned to each certificate • After that date, the certificate expires • A certificate can be renewed with a new expiration date assigned • If the keys are still valid and remain uncompromised
- 78. Certificate Revocation andSuspension • Reasons to suspend or revoke a certificate • A user leaves the company • A hardware crash causes a key to be lost • A private key is compromised • Revocation is permanent • Suspension can be lifted
- 79. Certificate Revocation andSuspension • Certificate Revocation List (CRL) • Contains all revoked and suspended certificates • Issued by CA's
- 80. HTTP Strict TransportSecurity • A header field in an HTTP response • Tells a browser to load this page securely (via HTTPS) • If the certificate is not valid, the browser will block access to that website
- 82. Backing Up Keys •Backing up keys is critical • If keys are destroyed and not backed up properly, encrypted business-critical information might be irretrievable • The CA is usually responsible for backing up keys • A key recovery policy is also part of the CA’s responsibility
- 84. Microsoft Root CA •You can set up your own Certificate Authority Server • Windows Server • Install Certificate Services
- 85. Microsoft Root CA •Specify options to generate certificates, including • Cryptographic Service Provider • Hash algorithm • Key length
- 86. Understanding Cryptographic Attacks •Sniffing and port scanning are passive attacks – just watching • Active attacks attempt to determine the secret key being used to encrypt plaintext • Cryptographic algorithms are usually public • Follows the open-source culture • Except the NSA and CIA and etc.
- 87. Birthday Attack • If23 people are in the room, what is the chance that they all have different birthdays? 365 364 363 363 361 360 343 365 x 365 x 365 x 365 x 365 x 365 x . . . 365 = 49% So there’s a 51% chance that two of them have the same birthday • See link Ch 12r
- 88. Birthday Attack • Ifthere are N possible hash values, • You’ll find collisions when you have calculated 1.2 x sqrt(N) values • SHA-1 uses a 160-bit key • Theoretically, it would require 280 computations to break • SHA-1 has no known collisions, but they are expected to be found soon
- 89. Mathematical Attacks • Propertiesof the algorithm are attacked by using mathematical computations • Categories • Ciphertext-only attack • The attacker has the ciphertext of several messages but not the plaintext • Attacker tries to find out the key and algorithm used to encrypt the messages • Attacker can capture ciphertext using a sniffer program such as Ethereal or Tcpdump
- 90. Mathematical Attacks • Categories •Known plaintext attack • The attacker has messages in both encrypted form and decrypted forms • This attack is easier to perform than the ciphertext-only attack • Looks for patterns in both plaintext and ciphertext • Chosen-plaintext attack • The attacker has access to plaintext and ciphertext • Attacker has the ability to choose which message to encrypt
- 91. Mathematical Attacks • Categories(continued) • Chosen-ciphertext attack • The attacker has access to the ciphertext to be decrypted and to the resulting plaintext • Attacker needs access to the cryptosystem to perform this type of attack
- 92. Brute Force Attack •An attacker tries to guess passwords by attempting every possible combination of letters • Requires lots of time and patience • Password-cracking programs that can use brute force • John the Ripper • Cain and Abel • Ophcrack • Also uses memory to save time – “Rainbow tables”
- 93. Man-in-the-Middle Attack • Victimsends public key to Server • Attacker generates two “false” key pairs • Attacker intercepts the genuine keys and send false keys out • Both parties send encrypted traffic, but not with the same keys • These false keys won’t be verified by a CA Victim Attacker Server
- 94. SSL/TLS Downgrade Attack •Attacker in the middle can alter a request • So that it appears to come from an old system, such as Windows 95 • Only capable of using old, broken ciphers, such as ones with 40-bit keys • Or "export-grade" encryption which was designed to be crackable by the US Gov't • Fix: configure server to only use secure ciphers
- 95. Dictionary Attack • Attackeruses a dictionary of known words to try to guess passwords • There are programs that can help attackers run a dictionary attack • Programs that can do dictionary attacks • John the Ripper • Cain and Abel
- 96. Replay Attack • Theattacker captures data and attempts to resubmit the captured data • The device thinks a legitimate connection is in effect • If the captured data was logon information, the attacker could gain access to a system and be authenticated • Most authentication systems are resistant to replay attacks
- 97. Firesheep • Replays cookiesto access others' accounts on wireless networks
- 98. Password Cracking • Passwordcracking is illegal in the United States • It is legal to crack your own password if you forgot it • You need the hashed password file • /etc/passwd or /etc/shadow for *NIX • The SAM database in Windows • Then perform dictionary or brute-force attacks on the file
- 99. Password cracking programs •John the Ripper • Hydra (THC) • EXPECT • L0phtcrack and Ophcrack • Pwdump • Ophcrack does it all for you – gathering the SAM database and cracking it
- 100. Recent SSL Vulnerabilities •Sslstrip MITM • Convert secure connection to insecure one • Works on mixed-mode authentication pages like Twitter (link Ch 12zj) • Written by Moxie Marlinspike
- 101. Recent SSL Vulnerabilities •Wildcard certificates • *%00.evil.com • Fools browser (link Ch 12zk) • Renegotiation vulnerability • Can break any SSL/TLS session (Ch 12zl) • Browsers often fail to check Certificate Revocation Lists • Untrustworthy CA entries in browser
- 102.
- 103. Which item isa list of invalid certificates? A. PKI B. CA C.Renewal D.Suspension E. CRL
- 104. What technique decryptsan encrypted message by trying all possible keys? A. Birthday B. Brute Force C. Man in the Middle D. Known Plaintext E. Dictionary
- 105. What technique defeats encryptionby impersonating a server? A. Birthday B. Replay C.Man in the Middle D.Known Plaintext E. Dictionary