This document discusses the history of encryption and cryptography. It covers early techniques like steganography and transposition ciphers where plaintext is rearranged. The Caesar and Vigenere ciphers are also explained, where letters are shifted or substituted according to a key. Modern encryption methods are then outlined, including public key infrastructure (PKI) which allows two parties to authenticate each other using digital signatures and public/private key pairs. The document traces encryption techniques over centuries and how they evolved with technological advances to the widespread use of encryption today to secure internet communications and banking.
8. The Caeser Cypher
In a Caeser cypher each letter of the alphabet is
shifted along some number of places;
Our message code is:
This code was invented by Julius Caeser
Move each letter on by three places of the
alphabet: e.g.
A→D
B→
C→
M→
9. Caeser Cipher
Split up into teams and try and identify the shift!
BPQA PIA JMMV APQNBML JG MQOPB
Speed up the decryption process:
Plain A B C D E F G H …
Cipher
10. Caeser Cypher Cont’d
• If the cipher alphabet can be any
rearrangement of the plain alphabet then
there are
- 400,000,000,000,000,000,000,000,000
combinations
11. Caeser Cipher
• How to crack the Caeser cypher
• Who plays Hangman?
• Advantage codebreakers
12. Advantage Codemakers
• The Vigenère cipher (1586) is a method of
encrypting alphabetic text by using a series of
different Caesar ciphers based on the letters
of a keyword.
• Key Difference is the use of a Keyword
• Lets use the keyword ‘CAR’ and the paintext to
be encrypted: ‘Its cold’
14. Vignere Cipher
• Break into teams
• Select a key and write the message:
• ‘Its not cold its freezing’
• Babbage versus Vignere:
– Pattern analysis using variation of differing length
in keywords
15. Summary so far:
• A cipher (or cypher) is an algorithm for
performing encryption and decryption — a
series of well-defined steps that can be
followed as a procedure.
• In most cases, that procedure is varied
depending on a key which changes the
detailed operation of the algorithm.
• The original information is known as
plaintext, and the encrypted form as
ciphertext.
17. The Age of the Machine and
Mathematicians
• DVD
18. Where we are today:
• In the mid-1970s, strong encryption emerged from
the sole preserve of secretive government agencies
into the public domain, and is now used in
protecting widely-used systems, such as Internet e-
commerce, mobile telephone networks and bank
automatic teller machines.
• Encryption can be used to ensure secrecy, but other
techniques are still needed to make
communications secure, particularly to verify the
integrity and authenticity of a message; for
example, a message authentication code (MAC) or
digital signatures.
19. SSL/TLS
• The TLS protocol(s) allow applications to
communicate across a network in a way designed
to prevent eavesdropping, tampering, and
message forgery. TLS provides endpoint
authentication and communications privacy over
a network using cryptography. Typically, only the
server is authenticated (i.e., its identity is
ensured) while the client remains
unauthenticated; this means that the end user
(whether an individual or an application, such as
a Web browser) can be sure with whom they are
communicating.
20. PKI
• The next level of security - in which both ends of the
"conversation" are sure with whom they are communicating -
is known as mutual authentication. Mutual authentication
requires public key infrastructure (PKI) deployment to clients.
• Public key cryptography, also known as asymmetric
cryptography, is a form of cryptography in which a user has a
pair of cryptographic keys - a public key and a private key. The
private key is kept secret, while the public key may be widely
distributed. The keys are related mathematically, but the
private key cannot be practically derived from the public key.
A message encrypted with the public key can be decrypted
only with the corresponding private key. The digital signature
of the signer is verified using the public key. This verification
process confirms that the message was not altered after the
digital signature.
