What is cryptography Ceasar Cipher Public key cryptography What is cryptography Cryptography or cryptology from Greek κρυπτός kryptós hidden secret and ID: 643288
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Slide1
Cryptography
Dr. XSlide2
Outline
What is cryptography?
Ceasar
Cipher
Public key cryptographySlide3
What is cryptography?
Cryptography
or
cryptology
(from
Greek
κρυπτός
kryptós
, "hidden, secret"; and
γράφειν
graphein
, "writing", or
-λογία
-logia
, "study", respectively
[1]
) is the practice and study of techniques for
secure communication
in the presence of third parties called
adversaries
.
(from Wikipedia)
https://www.khanacademy.org/computing/computer-science/cryptography/crypt/v/intro-to-cryptographySlide4
Types of cryptography
Symmetric: encryption
methods in which both the sender and receiver share the same key
Ex.
Ceasar
Cipher
What are the pros and cons?
Asymmetric/public key:
the public key may be freely distributed, while its paired private key must remain secret. In a public-key encryption system, the
public key
is used for encryption, while the
private
or
secret key
is used for decryption
.
Diffie
-Hellman
RSASlide5
Terminology
Key
Public
Private
Encryption key
Cipher
Plain textSlide6
One time pad
https://www.khanacademy.org/computing/computer-science/cryptography/crypt/v/one-time-pad
What are the pros and cons of this type of encryption?Slide7
Public key encryptionSlide8
Public key encryption
Choose p = 3 and q = 11
Compute n = p * q = 3 * 11 = 33
Public
key is (e, n) => (7, 33)
Private key is (d, n) => (3, 33)
The encryption of
m = 2
is
c = 2
7
% 33 = 29
The decryption of
c = 29
is
m = 29
3
% 33 = 2Slide9
Modulo Operation
%
Remainder of division
Ex. 5 % 4 = 1
If I was trying to divide 5 with 4, 4 can fit in 5 once and the remainder is 1
Practice:
100 % 3
35 % 4
18 % 19Slide10
Crypto exercise
Symmetric key cryptography with
Ceasar
cipher
Asymmetric key crypto with RSASlide11
Why do we need cryptography?
Internet is an open medium
Confidentiality
Integrity
…