Cyptography

Question 1

What is Confidentiality (Crypto) ?

Answer 1

Cryptography protects the confidentiality (or secrecy) of information. Even when the transmission or storage medium has been compromised, the encrypted information is practically useless to unauthorized persons without the proper keys for decryption.

Question 2

What is Integrity (Crypto) ?

Answer 2

Cryptography can also be used to ensure the integrity (or accuracy) of information through the use of hashing algorithms and message digests.

Question 3

What is Authentication (Crypto) ?

Answer 3

Cryptography can be used for authentication (and non-repudiation) services through digital signatures, digital certificates, or a Public Key Infrastructure (PKI).

Question 4

What is Monolithic Substitution ?

Answer 4

This system, which uses only a single alphabet to encrypt and decrypt an entire message.

Question 5

What is Cryptography ?

Answer 5

It is the science of encrypting and decrypting information, such as a private message, to protect its confidentiality, integrity, and/ or authenticity. Practitioners of cryptography are known as cryptographers.

Question 6

What is Cryptanalysis ?

Answer 6

Cryptanalysis is the science of deciphering (or breaking) ciphertext without the cryptographic key. Practitioners of cryptanalysis are known as cryptanalysts.

Question 7

What is Cryptology ?

Answer 7

Cryptology is the science that encompasses both cryptography and cryptanalysis. Practitioners of cryptology are known as cryptologists.

Question 8

What is a Plain Text Message ?

Answer 8

A plaintext message is a message in its original readable format or a ciphertext message that has been properly decrypted (unscrambled) to produce the original readable plaintext message.

Question 9

What is a CypherText ?

Answer 9

A ciphertext message is a plaintext message that has been transformed (encrypted) into a scrambled message that’s unintelligible.

Question 10

What is End to End Encryption ?

Answer 10

With end-to-end encryption, packets are encrypted once at the original encryption source and then decrypted only at the final decryption destination.

The advantages of end-to-end encryption are its speed and overall security.

However, in order for the packets to be properly routed, only the data is encrypted, not the routing information.

Question 11

What is Link Encryption ?

Answer 11

Link encryption Link encryption requires that each node (for example, a router) has separate key pairs for its upstream and downstream neighbors.

Packets are encrypted and decrypted, then re-encrypted at every node along the network path.

The advantage of using link encryption is that the entire packet (including routing information) is encrypted.

However, link encryption has the following two disadvantages:

Latency: Packets must be encrypted/ decrypted at every node, which creates latency (delay) in the transmission of those packets. Inherent vulnerability:

If a node is compromised or a packet’s decrypted contents are cached in a node, the message can be compromised.

Question 12

What is a KeySpace ?

Answer 12

A keyspace is the range of all possible values for a key in a cryptosystem.

Question 13

What is a CryptoSystem ?

Answer 13

A cryptosystem consists of the cryptographic algorithm (cipher) and the cryptovariable (key), as well as all the possible plaintexts and ciphertexts produced by the cipher and key.

An effective cryptosystem must have the following properties:

The encryption and decryption process is efficient for all possible keys within the cryptosystem’s keyspace.

Question 14

What is a Restricted Algorithm ?

Answer 14

A restricted algorithm refers to a cryptographic algorithm that must be kept secret in order to provide security. Restricted algorithms are not very effective, because the effectiveness depends on keeping the algorithm itself secret rather than the complexity and high number of variable solutions of the algorithm, and therefore are not commonly used today.

Generally used only for applications that require minimal security.

Question 15

What is a Crypto Variable ?

Answer 15

Also called a key, the cryptovariable is a secret value applied to the algorithm. The strength and effectiveness of the cryptosystem largely depend on the secrecy and strength of the cryptovariable.

Question 16

What is a Crypto Algorithm ?

Answer 16

Also called a cipher, the cryptographic algorithm details the step-by-step mathematical function used to produce • Ciphertext (encipher)
• Plaintext (decipher)

Question 17

What is Key Clustering ?

Answer 17

Key clustering (clustering) occurs when identical ciphertext messages are generated from a plaintext message by using the same encryption algorithm but different encryption keys.

Key clustering indicates a weakness in a cryptographic algorithm because it statistically reduces the number of key combinations that must be attempted in a brute force attack.

Question 18

What are the two main classes of Cyphers ?

Answer 18

The two main classes of ciphers used in symmetric key algorithms are:
block
stream

Question 19

What are Block Cyphers ?

Answer 19

Block ciphers operate on a single fixed block (typically 64 bits) of plaintext to produce the corresponding ciphertext. (Mostly software based)

Using a given key in a block cipher, the same plaintext block always produces the same ciphertext block.

Advantages of block ciphers compared with stream ciphers are:
Reusable keys: Key management is much easier. Interoperability: Block ciphers are more widely supported.

Question 20

What are Stream Cyphers ?

Answer 20

Stream ciphers operate in real time on a continuous stream of data, typically bit by bit. Stream ciphers generally work faster than block ciphers and require less code to implement. However, the keys in a stream cipher are generally used only once and then discarded.

Key management becomes a serious problem. Using a stream cipher, the same plaintext bit or byte will produce a different ciphertext bit or byte every time it is encrypted.
Stream ciphers are typically implemented in hardware.

Question 21

What are the two types of Cypher ?

Answer 21

The two basic types of ciphers are:
substitution
transposition.

Question 22

What is a Substitution Cypher ?

Answer 22

Substitution ciphers replace bits, characters, or character blocks in plaintext with alternate bits, characters, or character blocks to produce ciphertext.

Example: Caesar Cypher.