Cryptography. Troy Latchman Byungchil Kim. Fundamentals. We know that the medium we use to transmit data is insecure, e.g. can be sniffed. Cryptography allows a sender to disguise data in hopes that an intruder can gain no information from the intercepted data. Fundamentals.
Caesar cipher is a very old and simple symmetric key algorithm:
Caesar cipher example:
Note that Caesar cipher only has 25 possible keys, so a brute force method to break the encryption can be used.
Monoalphabetic cipher - an improvement over Caesar cipher
Basic operation of DES
Overview of public key encryption
Kb-(Kb+(m)) = m
IMPORTANT: Kb+(Kb-(m)) = m
(We will see the importance of this later)
RSA – a public key encryption algorithm named after its founders (Ron Rivest, Adi Shamir, and Leonard Adleman):
where ‘m’ is the numeric value of the letter and ‘c’ is the cipher output
where ‘m’ is the recovered message
Bob does the following:
- Thus, n=35 and z=24
So we have Kb+ = (35,5) and Kb- = (35,29)
Suppose Alice wants to send ‘l’ ‘o’ ‘v’ ‘e’ to Bob…
(This is the important part from slide 16)
Kb-(H(m)) which is called a digital signature
Directly from ‘m’ (like Bob did when sending the message)
By applying Bob’s public key to the digital signature: Kb+(Kb-(H(m)) = H(m)
MD5 computes a 128-bit message digest in a four-step process.
All figures and tables throughout this presentation came from one source: