EXAM 1 Flashcards
What is ciphertext
Message after transforming it with encryption
What is Encryption?
Converting plaintext to ciphertext
What is Decryption?
Restoring plaintext from ciphertext
What is a Cipher?
The algo that can take plaintext and convert it to ciphertext, (it goes both ways)
What is Cryptanalysis?
The science of breaking ciphers
What is Cryptology?
Cryptography + Cryptanalysis
How are encryption algorithms classified?
How do they convert plaintext to ciphertext
How many keys they require
How do they process the plaintext
How do substitution ciphers work?
Replacing elements of plaintext, with elements of ciphertext
How do Transposition ciphers work?
Shuffle the elements of the plaintext
How do Product Ciphers work?
Combine Substitution, and Transposition
What is Symmetric Encryption?
Single key used for encryption and decryption
What is Asymmetric (public Key) cryptography?
Two-keys, one is used for encryption, the other is used for decryption.
Asymmetric (public Key) cryptography is commonly used for…
session key distribution, and digital signatures.
What is the difference between a block and stream cipher?
Stream does 1 by 1, block does multiple at a time.
What are the security requirements for secure symmetric key cryptography?
- Strong encryption algorithm,
- Assumption that attacker knows knows the encryption algorithm
- Trusted third party, to distribute the key
What is Kerckhoff’s Principle?
Everything must remain secure even if the attacker knows everything EXCEPT the secret key.
If an attacker finds, a secret message and modifies it what violation is it?
Integrity violation, Data integrity
What is Data Integrity?
Assurance that data received is sent by someone trusted.
What is origin integrity
The source of the data is trustworthy
What is DAD?
Disclosure, Alteration, Destruction
What three main aspects of security does ITU-T X.800 consider?
Services
Attacks
Mechanisms
What is a Passive attack?
An attack that does not involve the modification of systems or data.
What types of passive attacks are there?
Eavesdropping
Traffic Analysis
How do we protect against traffic analysis?
Traffic padding
Why are passive attacks so difficult to detect?
They don’t involve any kind of tampering
What are types of active attacks?
Masquerade - Pretending to be someone else
Replay - Data transmission gets repeated or delayed
Message Modification
Denial of Service
What is an active attack?
An attack that modifies systems or data
What is Traffic padding?
Putting bits into gaps in a data stream to make it difficult to figure out the amount of traffic
What are the three main elements of network security?
- algorithm for security transformation
- Generate secret keys
- Distribute and share keys
What is the difference between the internet and the Web?
A web is a protocol.
The internet refers to the entire infrastructure
What is a protocol?
A set of rules that govern communication
What is the primary objective of data classification? How does it relate to cryptography?
Securing data based on assigned level of importance and sensitivity it relates because Cryptography is used a defense mechanism for data
What is FIPS-140? What does it provide?
set of standards for designing and implementing modules that defend sensitive / classified data
For what type of government systems was FIPS-140 compliance designed for?
It was designed for data that is sensitive but unclassified
Describe the Top-Secret data category. What type of data does it contain?
Give examples.
Nuclear secrets, locations of space satellites
Give some examples of FIPS-140 requirements
Finite State model
Physical Security
Operational Environment
What is the difference, between brute force and cryptanalytic attack?
Brute force tries every possible key, Cryptanalytic uses nature of algorithm AND some knowledge of the plaintext
what is a chosen-plaintext
attack?
Attacker can encrypt any plaintext using the target encryption scheme.
What is ciphertext-only attack?
Stat techniques to discover the key or plaintext
what is a known-plaintext attack?
Has access to the cipher text and knows some properties of the plaintext
Describe the requirements and the basic building blocks of public cryptography
Two keys, public and private. Encrypt with public and use private to decrypt.
Is public key cryptography inherently more secure than symmetric key cryptography
No, public key is less efficient
What is the difference between the RSA and EC approaches to public key cryptography?
RSA is based on the difficulty of factoring large primes
EC is based on Elliptical curves over finite fields
What is the Elliptic Curve Discrete Logarithm Problem (ECDLP)?
Find K given P and Q, on a curve where Q = kP
How can quantum cryptography theoretically threaten the security of public key schemes
such as RSA?
Quantum computers in theory are able to solve RSA fast
What is a hash function?
one way function that takes a message and produces a fixed-size output
What is a hash function used for?
Used for message integrity, and Digital Signatures
What are the security requirements of the hash function?
- Can work with any sized M
- Produces fixed length output
- Easy to compute hc
- No repeating hash values
Describe the basic premise of a Birthday attack and be able to do simple probability
calculations.
2^(n/2) give you 50% chance to find a match
How can the Birthday Paradox be used to crack hashes?
- Generate 2^(n/2) random messages
- Do any two messages produce the same hash?
- Hash detected
- If not go back to step 1.
What is the difference between a hash function and a MAC?
input is variable sized, One way function that computes the digest BASED ON a Secret Key,
Compare and contrast symmetric cryptography and a MAC function.
Symmetric: Length of plaintext varies so does length of cipher text
Mac function always gives a digest of the same length, and are non invertible.
Why do we (ideally) need both link and end-to-end encryption?
Data is always protected, and our headers are still protected on the link
What is symmetric key distribution? Why is it important?
changing keys every time you start a new session, incase the previous was compromised
Explain the key hierarchy
Decentralized: each person needs a master key
Centralized: Trusted third party only need N mater keys.
Why use symmetric master keys to distribute session keys?
It’s a good idea to change session keys with every session
What are key components of Symmetric Needham-Shroeder Key Distribution protocol
A Asks, KDC Shares, A Forwards, B Responds, A Confirms.
Why does KDC echo Alice’s message in step (2)?
So Alice knows the session key is for her session with bob and it also has a Nonce
How does the protocol use nonces
and time stamps to prevent replay attacks?
if checks if any nonces have been used before
Is Alice able to decrypt entire message from the KDC? Explain
No, she can only decrypt the first part that used her master key
What are the advantages of using a hierarchy of KDCs?
It reduces the load of any single KDC
Assume a key distribution scheme where Bob and Alice both share the
symmetric master key MBA. To distribute the session key Alice generates the session
key KS encrypts it using MBA and sends the message IDA || E(MBA,KS).
Vulnerable to a replay attack, no nonce or timestamp
Why use public key cryptography to distribute session keys? That is, why not just use public key encryption to send bulk data?
Public key cryptography is too slow.
Consider the Merkle Simple Key Distribution protocol. Is it secure? If
so, explain how so and if not so, explain the flaw.
Not secure, There is no public key authenticity
Explain how distribution of symmetric keys using public keys can be combined with the
Symmetric Key Needham Shroeder protocol for greater efficiency.
Use secure public to distribute master keys.
After master keys are distributed use Needham to distribute session keys, we don’t need public until we give out master keys again
