Cryptology Flashcards
Encryption is…
A method of transforming readable data, called plaintext, into a form that appears to be random and unreadable, which is called ciphertext. It can be created through hardware components or program code in an application
Cryptosystem is
A system or product that provides encryption and decryption.
Algorithm
The set of rules also known as Ciphers, dictates how enciphering and deciphering take place.
In Encryption, the Key also known as cryptovariable
Is a value that comprises a large sequence of random bits.
Algorithm contains keyspace, which
Is a range of values that can be used to construct a key.
When algorithm need to generate a new key, it uses random value from the keyspace
Cryptosystem encompasses all the necessary components for encryption and decryption to take place. A Cryptosystem is made up of at least the following:
- Software
- Protocols
- Algorithms
- Keys
Example of a Cryptosystem
Pretty Good Privacy (PGP)
Crytosystems can provide the following services:
- Confidentiality
- Integrity
- Authentication
- Authorization
- Nonrepudiation
Cryptography is
Practice of storing and transmitting information in a form that only authorized parties can understand
Kerckhoff’s Principle:
August Kerckhoffs published a paper in 1883
Stating that the only secrecy involved with a cryptography should be the key. He claimed that the algorithm should be publicly exploit.
The strength of an encryption method comes from:
- the algorithm
- the secrecy of the key
- the length of the key
- how all work together within a cryptosystem
Breaking Cryptosystem can be accomplished by a….
Brute-force attack
Another name for cryptography strength is_____
Workfactor (work function), which is an estimate of the effort and resources it would take an attacker to penetrate a cryptosystem
(Time and effort to break a protective measure)
One-Time Pad, which is invented by Gilbert Vernam in 1917 (aka Vernam Cipher) is a ______
Perfect encryption scheme because it is considered unbreakable if implemented properly
One-Time pad is made up of random bits. This encryption process uses a binary mathematic function called…..
Exclusive-OR (XOR)
XOR (exclusive-OR) is an operation that is applied to 2 bits. When combing the bits: if both values are same the result is ____. If the bits are different from each other, the result is ____.
1 XOR 1 = 0
1 XOR 0 = 1
One-Time pad Requirements. (To be successful)
- Made up on truly random values
- Used only one time
- securely distributed to its destination
- secured at sender’s and receiver’s sites
- At least as long as the message
The Cryptographic life cycle is the….
Ongoing process of identifying your cryptography needs, selecting the right algorithms, provisioning the needed capabilities and services, and managing keys.
Cryptographic methods
- Symmetric Key (aka Secret key)
- Assymmetric key (Public and private key)
A variant of the approach is called ECC ( Elliptic Curve Cryptography)
Symmetric Key Cryptography:
- the sender and receiver use two instances of the same key for encryption and decryption.
- Key has dual functionality, it carry both encryption and decryption processes.
- Also called Secret Keys
- one separate key for each friend or receiver.
- depends on how well users protect their secret keys
- Provide confidentiality
- examples: AES (Advanced Encryption Standard) and ChaCha20
Advantages Symmetric Key
- Much Faster
- Hard to break if using a large key size
Block Ciphers
- Is used for encryption and decryption purposes, the message is divided into blocks of bits.
- these blocks are then put through mathematical functions, one block at a time.
A strong Cipher contains right level of 2 main attributes: Confusion and Diffusion….
- Confusion: is commonly carried out by substitution
- Diffusion: is carried out by using transposition
More on Confusion and Diffusion:
In algorithms,
- diffusion takes place as individual bits of a block are scrambled, or diffused, throughout that block.
- Confusion is provided by carrying out complex substitution functions so the eavesdropper cannot figure out how substitute the right values and come up with the plaintext.
Avalanche effect
- If the input to an algorithm is slightly modified, then then the output of the algorithm is changed significantly.
- So a small change to the key or the plaintext should cause drastic changes to the resulting ciphertext.
The ideas of Diffusion and Avalanche effect are basically the same. True or False
True
Who came up with Avalanche Term and Diffusion:
Avalanche: Horst Feistel
Diffusion: Claude Shannon
Stream Cipher
- A Steram Cipher does not divide a message into blocks. Instead, treats the message as a stream of bits and perform mathematical functions on each bit individually.
Stream Ciphers use…..
Keystream Generators, which produce a stream of bits that XORed with the plaintext bits to produce ciphertext.
Initialization Vector (IV)…
- Initialization Vectors are random values that are used with algorithms to ensure patterns are not created during the encryption process.
- they are used with keys and do not need to be encrypted when being sent to the destination.
If Initialization Vector (IV) are not used…
Then two identical plaintext values that are encrypted with the same key will create the same two identical plaintext values that are encrypted with the same key will create the same ciphertext.
What are the characteristics of a strong effective stream ciphers?
- Easy to implement Hardware
- Long periods of no repeating patterns within keystream values
- a keystream not linearly related to the key
- Statistically unbiased keystream (as many zeroes and ones)
Asymmetric Key Cryptography
- In Public Key systems, each entity has different, asymmetric keys.
- Two different asymmetric keys are mathematically related.
- If message is encrypted by one key, the other key is required to decrypt the message.
- One key is called public and the other one private.
- The public key is known to everyone, and the private key only known to the owner
Asymmetric | Secure Message Format
- If confidentiality is the most important security service to a sender, she would encrypt the file with the receiver’s public key.
- This is called a secure message format because it can only be decrypted by the person who has the corresponding private key.
Asymmetric | Open Message Format
- If authentication is the most important security service to the sender, then she would encrypt the data with her private key.
- Encrypting data with the sender’s private key is called an open message format.
Strengths of Asymmetric key Crytosystems
- Better key distribution than symmetric systems
- Better scalability than symmetric systems
- can provide authentication and Nonrepudiation
- Examples: RSA, ECC, DSA
Symmetric | Asymmetric: Use
- Symmetric: Bulk encryption, which means encrypting files and communication path
- Asymmetric: Key Distribution and Digital Signatures
Symmetric | Asymmetric: Security Services Provided
- Symmetric: Confidentiality
- Asymmetric: Confidentially, Authentication, and Nonrepudiation