Intro to Cryptography Flashcards
What is Kerckhoffs’s Principle
A crypto system should be secure, even if everything about the system, except the key, is public knowledge
How is Kerckhoffs’s principle relevant in encrypted communications?
It allows for the possibility that the entire encrypted message and even the encryption algorithm used to produce it, may be intercepted by an attacker without compromising the overall security of the system
What is an algorithm in Cryptography?
A set of rules that dictate how we encode and decode
What are the 4 main goals of Cryptography?
1) Confidentiality
2) Integrity
3) Authentication
4) Nonrepudiation
What does cryptography do in terms of confidentiality and what are the two main cryptosystems?
Keeping data confidential in rest, transit and during processing
Symmetric Cryptosystems (shared secret key)
Asymmetric Cryptosystems (public and private keys)
How is cryptography used for Integrity?
Ensures data has not been altered in any way without authorisation
Designed to ensure information is not altered/deleted by malicious third party or by accident
Message integrity established through use of encrypted message digests (digital signatures)
How is cryptography used in authentication?
Ensures that the identity of a user is valid and verified
I am who I say I am (challenge and response encryption)
How is Nonrepudiation used in cryptography?
Provides assurances to the recipient that the message originated from the sender and not someone else, pretending to be the sender
Prevents the sender denying that they sent the message
Provided by public key cryptosystems
What is the difference between a code and a cipher?
A code is not always secret and used more to prevent ambiguity (sounding the same). Substitute arbitrary symbols
Ciphers are designed to hide the true meaning of the information
Ciphers use algorithms to transform a message into an apparently random string of characters
Converts plain text to cipher text
What is a Transposition Cipher?
One of the most simple ciphers
Uses an algorithm to rearrange the letters of plain text to create a cipher text e.g. apple reversed to “elppa”
How can the complexity of transposition ciphers be increased?
Using columnar transposition
How does columnar transposition work?
Remove all the spaces between the words
Write the message in (4) rows of (7) columns
Read the letters in order down the columns instead of along the rows
What is a Caesar Cipher?
AKA ROT3 (rotate 3)
Imagine the alphabet written on a wheel
Encrypt by shifting each letter 3 letters to the right
(A becomes D, B becomes E)
Decrypt by rotating to the left
Could be a rotate 4, 5, 6…..
What makes a good Caesar Cipher?
Can handle any rotation
Can handle upper case and lower case without drifting into special characters
