elementary cryptography steven bogaerts n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Elementary Cryptography Steven Bogaerts PowerPoint Presentation
Download Presentation
Elementary Cryptography Steven Bogaerts

Loading in 2 Seconds...

play fullscreen
1 / 26

Elementary Cryptography Steven Bogaerts - PowerPoint PPT Presentation


  • 106 Views
  • Uploaded on

Elementary Cryptography Steven Bogaerts. Goal of Cryptography. Ensure security of communication over insecure medium Privacy (secrecy, confidentiality) Integrity Communicate even with possibility of adversaries. Approaches to Secure Communication. Steganography Hide message existence.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Elementary Cryptography Steven Bogaerts' - pembroke


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
goal of cryptography
Goal of Cryptography
  • Ensure security of communication over insecure medium
    • Privacy (secrecy, confidentiality)
    • Integrity
  • Communicate even with possibility of adversaries
approaches to secure communication
Approaches to Secure Communication
  • Steganography
    • Hide message existence
  • Cryptography
    • Hide message meaning
cryptosystem
Cryptosystem
  • How does this help us accomplish our goals?
    • Privacy
    • Integrity
security failures
Security Failures
  • Privacy failure
    • Intercept
  • Integrity failure
    • Modify
    • Fabricate
  • Block
encryption algorithms
Encryption Algorithms
  • Two categories:
    • Keyless
    • Keyed
      • Symmetric
      • Asymmetric
  • Character representation
    • A=0, B=1, ..., Z=25
    • So A + 3 = D, etc.
substitution ciphers
Substitution Ciphers
  • Replace each letter with another
  • Caesar cipher
    • ci = E(pi) = pi + 3
    • Ex: THE EAGLE HAS LANDEDwkh hdjoh kdv odqghg
    • Easy to memorize
    • In general: ci = E(pi) = pi + n
other substitution ciphers
Other Substitution Ciphers
  • Key: "professional"ABCDEFGHIJKLMNOPQRSTUVWXYZprofesinalbcdghjkmqtuvwxyz
  • Every third letterABCDEFGHIJKLMNOPQRSTUVWXYZadgjmpsvybehknqtwzcfilorux
cryptanalysis
Cryptanalysis
  • Brute force: 26! possibilities
  • Hints:
    • Frequencies:
      • Letter (general)E, T, A, O, N, I, R, ...
      • First letter
      • Last letter
    • Guesses at message content
  • Double letter
  • Digraphs, trigraphs
  • Small words
cryptanalysis1
Cryptanalysis
  • Example:

wklv phvvdjh lv qrw wrr kdug wr euhdn

cryptanalysis2
Cryptanalysis
  • Example:

wklv phvvdjh lv qrw wrr kdug wr euhdn

  • wrr --> see, too, add, odd, off...wr --> to, ofBest guess: w = T, r = O
cryptanalysis3
Cryptanalysis
  • Example:

wklv phvvdjh lv qrw wrr kdug wr euhdn

  • wrr --> see, too, add, odd, off...wr --> to, ofBest guess: w = T, r = O
  • lv --> so, is, in, ...T_SO very unlikely...T_IS likelyBest guess: l = I, v = S
cryptanalysis4
Cryptanalysis
  • Example:

wklv phvvdjh lv qrw wrr kdug wr euhdn

  • wrr --> see, too, add, odd, off...wr --> to, ofBest guess: w = T, r = O
  • lv --> so, is, in, ...T_SO very unlikely...T_IS likelyBest guess: l = I, v = S
  • wklv phvvdjh lv qrw wrr kdug wr euhdnT-IS --SS--- IS -OT TOO ---- -- -----
cryptanalysis5
Cryptanalysis

wklv phvvdjh lv qrw wrr kdug wr euhdn

THIS MESSAGE IS NOT TOO HARD TO BREAK

  • Regularity
  • Outside information
cryptanalysis6
Cryptanalysis

wklv phvvdjh lv qrw wrr kdug wr euhdn

THIS MESSAGE IS NOT TOO HARD TO BREAK

  • Regularity
  • Outside information
  • WWII: af to be target of a major assault
    • "Damaged" water distillery
one time pad
One-Time Pad
  • Avoid regularity
  • Vernam Cipher exampleKey: CIHJTFDJZMEPQLFHXYRLS...Plaintext: HELLOCIHJT 2 8 7 9 19HELLO + 7 4 11 11 14 9 12 18 20 7 7 = 33 mod 26Ciphertext: J M S U HRemaining key: FDJZMEPQLFHXYRLS...
one time pad1
One-Time Pad
  • Hard to maintain keys
  • Facilitate key distribution
    • Novel
    • Phone book
transposition
Transposition
  • (Substitution - replace one letter with another)
  • Transposition - mix up plaintext message
    • Columnar
transposition1
Transposition
  • (Substitution - replace one letter with another)
  • Transposition - mix up plaintext message
    • Columnar: T A L L C OM P U T E RS C I E N TI S T S R OC K x k g j-->tmsicapcskluitxlteskcenrgortoj
much more to discuss
Much More To Discuss...
  • What makes a "good" encryption algorithm
  • Data Encryption Standard (DES)
    • Double and Triple DES
  • Advanced Encryption Standard (AES)
  • Public Key Encryption
    • Rivest-Shamir-Adelman (RSA)
summary so far
Summary So Far
  • Maintain privacy, integrity despite adversaries
  • Cryptosystems
    • Substitution
    • Transposition
  • Cryptanalysis
bible codes
Bible Codes?
  • Equidistant Letter Sequences (ELS)
  • Rips, Witztum in Statistical Science
    • Reviewers not convinced, but nothing formally wrong
bible codes1
Bible Codes?
  • Refutations
    • McKay, Bar-Natan, Kalai, Bar-Hillel in Statistical Science
    • Moby Dick "predicts" assassinations
scripture
Scripture
  • "... Ask and it will be given to you; seek and you will find; knock and the door will be opened to you." (Luke 11:9)
  • "...the counselor, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you." (John 14:26)
  • "The secret things belong to the LORD our God, but the things revealed belong to us and to our children forever, that we may follow all the words of this law." (Deuteronomy 29:29)