Lecture 4 Flashcards
What is Cryptography?
Keeping messages secure
What is Decryption?
Transformingencrypted messages back to its original form
What is Cryptosystem?
A system that combines both encryption and **deencryption **
Wjhat is Cryptanalysis?
Breaking the cryptosystems (used by hackers)
What is Plaintext?
Unencrypted “meaningful” text into a certain language
What is Ciphertext?
Any encrypted text in the given language
What is Polyalphabetic Cipher?
Where plaintext characters are mapped onto several possible characters in the cipher text depending on the position of the input character
What is Transposition Cipher?
- Block ciphers
- Designed to conceal a message content by rearranging its characters, rather than alphabet either within or across the blocks
Cryptanalysis Techniques & Tools
A Cryptanalysis works with:
- Encrypted messages
- Intercepted plaintext
- Known encryption algorithms
- Data items suspected to be in cipher text
A Cryptanalyst tools include:
- Mathematical and statistical techniques
- Computers with plenty of processing power
- Statistical properties of language
What are the modern Cryptography?
- Symmetric Encryption
- Asymmetric Encryption
- Hashing
What is Symmetric Key?
Known as “conventional key” or “secret key” =
“SECRET COMMUNICATION”
Technique to provide confidentiality, transmitted and stored data
- Used to encrypt and decrypt message
- Send and receiver of the message share a single and common key used to encrypt and decrypt a message
- If someone discovers the key, the plain text is readable
- Simple and faster
Disadvantages of Symmetric Key
Two parties must:
- Obtain copies of the secret key
- exchange the key in a secure way
Five ingredients to Symmetric Encryption
- Plain text: original data that is placed into the algorithm
- Encryption algorithm: performs substitutions and transformation performed by the algorithm depending on the key
- Secret key: The secret key is placed in the encryption algorithm which performs transformation depending on the key
- Ciphertext: Scrambled text to produce an output; depending on the plaintext and secret key. Two different key will produce two different ciphertext.
- Decryption algorithm: Ciphertext and secret key to transform back to plaintext
Symmetric Encryption – What is Block VS Stream
Block Cipher
- are most commonly used in symmetric encryption algorithms
- Processes plain text into fixed-size blocks, then a block -> cipher text, equal size for each plain text block
- Reusable keys
Examples: DES (Data Encryption Standards), 3DES (Triple Data Standards) and AES (Advances Encryption Standards)
Stream Ciphers
- Input element continuously
- Produces one element a time
- Encrypts one byte (8bits) a time from small to large chunks a time
