Chapter 2 - Basic Terminology Flashcards
What is cryptography?
- The making and breaking of codes and ciphers
What is ‘plain text’?
- The message or document that you wish to keep secret
What is another way to refer to ‘plain text’?
- Clear text
What format is ‘clear text’ in?
- Some language the sender and receiver can both understand
What is a cipher?
- A message or algorithm for garbling a message to make it unreadable
What do ciphers operate on?
- individual characters or groups of characters in the text without regard to their meaning
What is a key?
- A secret piece of information known only to the sender and legitimate receiver
What does the strength of a cipher depend on?
- on the total size of the keys it uses
What is another way of refer ‘key word/phrase’?
- a word or phrase used as a key
What is encryption?
- The process of changing the plaintext into an unreadable garble by the legitimate sender who knows the key
What is another way of referring to ‘encryption’?
- Encipherment
What is ‘cipher text’?
- The process of changing the plaintext into an unreadable garble by the legitimate sender who knows the key
What is ‘decryption’?
- The process that the legitimate receiver, who knows the method and the key, uses to turn the garbled ciphertext back into the original plaintext message.
What is another way of referring to ‘decryption’?
- Decipherment
What is a ‘Code’?
- A method for garbling a message to make it unreadable
How is a ‘Code’ different from a cipher?
- A code normally operates on words or phrases or phrases in a message
What is cryptology?
- The formal study of cryptography. Includes the study of mathematics and methodologies used for constructing and solving ciphers
What is Cryptanalysis?
- The study of codes and ciphers for the specific purpose of identifying weaknesses and finding ways to break them or to strengthen them
What is ‘Code Breaking’?
- The process of solving encrypted messages by third parties who do not have the key and may not have the method either
What is meant by an unbreakable cipher?
- Can’t be broken by cryptographic means
- The cipher can’t be broken in a practical sense
What information do you need when choosing a cipher?
- How much compute and man power your opponents can expend on breaking your cipher
When do you have an unbreakable cipher?
- When the cipher meets a target that is conservative and takes into account for advances in compute power considering your opponents compute and man power
What is a key factor when choosing and unbreakable cipher for it?
- the lifespan of a message.
When has a cipher been broken?
- When an opponent can read messages using the cipher
What is the collective term for all methods of hiding a message?
- Steganography
What are the 3 categories of modern ciphers?
- Secret Key
- Public Key
- Personal Key
What is a ‘secret key’ cipher?
- Sender has a secret key used to encipher a message
- Receiver has the corresponding secret key used to decipher the message
What is a core property of a ‘key’ in a ‘secret key’ cipher?
- Keys between sender and receiver can be the same or the inverse
Who usually controls the ‘key’ in a ‘secret key’ cipher?
- The sender
What happens when the sender changes the ‘key’ in a ‘secret key’ cipher?
- The sender must send the new key(or it’s inverse) to the receiver
What is a ‘public key’ cipher?
- The receiver has a public key known to everyone. The sender uses the public key to encipher the message.
- The receiver has a secret decryption key known only to them. This key is used to decipher the message.
What is a key factor allowing a ‘public key’ cipher to work?
- The secret key can’t be computed from the public information
What is the dominate ‘public key’ cipher?
- RSA algorithm
What is a ‘person key’ cipher?
- Sender and Receiver each have a personal key they don’t share with anyone
What are the steps a sender and receiver follow when using a ‘person key’ cipher?
- pass 1 - sender enciphers the message with personal key
- pass 2- receiver enciphers the received message with personal key and sends the message back to sender
- pass 3 - sender deciphers the message from receiver using personal key and sends this back to receiver
after pass 3 the message is enciphered with the receivers key and receiver deciphers the message
What is tricky about a ‘person key’ cipher?
- You have to get the same result if sender encrypts first or the receiver encrypts first
What is another way of referring to a ‘personal key’ cipher?
- “Three pass protocol”
What is the benefit of a ‘personal key’ cipher?
- The sender and receiver can communicate securely without having to prearrange or transmit any key so there’s no possibility of a key being intercepted.
What is a ‘person key’ cipher?
- Sender and Receiver each have a personal key they don’t share with anyone
What is a key characteristic of ‘public key’ cryptography?
- Sender and Receiver each have a secret key
- Sender and Receiver each have a public key available to everyone
What is a key characteristic of ‘secret key’ cryptography?
- All keys are kept secret
What is categorizing a cipher as ‘symmetric’ or ‘asymmetric’ not particularly useful
- The terms fail to capture the essential difference between public and private key cryptography
What do block cyphers operate on?
- Blocks of characters in the message
How are blocks usually sized in a ‘block cypher’?
- Blocks are usually the same size
What is the usual size of a key that is used in a ‘block cypher’?
- Keys are the same size for every block
What do ‘stream cyphers’ operate on?
- They operate on one character at a time
What is a key characteristic of a key used in a ‘stream cipher’?
- The keys are different for every character
What is the name of a key associated with a character in a ‘stream cipher’?
- Its called the ‘character key’
Where does the character key in a ‘stream cipher’ usually come from?
- It comes from a larger key called the ‘message key’
In older stream ciphers what is a common characteristic of a message key?
- The message key is repeated
What is a cipher called if it has regularly repeating keys?
- Periodic
For newer stream ciphers what is a common characteristic
- The message key is usually as long as the message
For newer stream ciphers what is a message key called?
- A ‘key stream’
What is the difference in speed when comparing secret key vs public key cryptography?
- Secret key cryptography is much faster then public key cryptography
What is the main use of public key cryptography?
- To encrypt the keys that are used for secret key encryption
What kind of attacks is public key cryptography subject to?
- Man in the middle attacks
What kind of attacks is public key cryptography subject to?
- Man in the middle attacks
What is very important in order for public key encryption to work?
- Authentication and verification of sender and receiver
How is public key encryption different from private key encryption in terms of administrative load?
- A lot of messages sent back and forth between sender and receiver for public key encryption. There is no such overhead with private key encryption
Where is public key encryption not suitable?
- When ensuring secrecy of data files stored on a computer
What is the current standard cipher?
- AES
What is the most common public key encryption method?
- RSA
