TTM4135: Information Security
# Definitions
These are definitions found in course material (mostly exercises) which may prove useful for the exam
##Chapter 1
|| Confidentiality || preventing unauthorised disclosure of information ||
|| Integrity || preventing unauthorised (accidental or deliberate) modification or destruction of information ||
|| Availability || ensuring resources are accessible when required by an authorised user ||
|| Entity authentication || provides confirmation of the claimed identity of an entity ||
|| Data origin authentication || provides confirmation of the claimed source (origin) of a data unit (message) ||
|| Non-repudiation || Placeholder ||
|| Cipher || See own section ||
|| Kerckhoffs’ principle || the cryptanalyst has complete knowledge of the cipher, i.e. only unknown thing is the decryption key ||
|| Transposition || the characters in the plaintext are mixed up with each other (permuted) ||
|| Substitution || each character (or set of characters) is replaced by a different character (or set of characters) ||
## Chapter 2
|| confusion || This involves substitution to make the relationship between the key and ciphertext as complex as
possible. ||
|| diffusion || This involves transformations that dissipate the statistical properties of the plaintext across the ciphertext.
||
|| product cipher || A product cipher is a cryptosystem in which the encryption function is formed by applying (or composing) several sub-encryption functions.||
|| iterated cipher || Most modern ciphers in this category, read more below ||
|| Feistel cipher || placeholder||
|| substitution-permutation network || placeholder||
|| group generator || placeholder||
|| finite field || placeholder||
TODO: Scrape definitions from all exercises (currently they are just from exercise 1)
# Ciphers
## Symmetric cipher
(secret key cipher) encryption and decryption keys known only to sender and receiver. (DES)
## Asymmetric cipher
(public key cipher) each participant has a public key and a private key, may allow both encryption and signatures. (RSA)
## Attacks
### Ciphertext only attack
the cryptanalyst has available only the intercepted cipher text.
### Known plaintext attack
the cryptanalyst knows a small amount of plaintext and its cipher text equivalent
### Chosen plaintext attack
The cryptanalyst can obtain the cipher text equivalent of some plaintext which can be selected by the attacker, i.e the attacker has an "inside encryptor” available
### Chosen cipher text attack
The cryptanalyst can obtain the plaintext equivalent of some cipher text which can be selected by the attacker, i.e. the attacker has an “inside decryptor” available.
## Block ciphers
### Block cipher modes
## Stream ciphers
## Historical ciphers
- Caesar
- Substitution
- Vigenère. Caesar, but also uses a key in order to choose how many steps to shift the alphabet for each letter
### DES
### AES
### RSA
# Iterated ciphers
- Encryption process divided into _r_ similar rounds
- the sub encryption functions _g_ are the same for all rounds
- Each key $K_i$ is derived from the overall master key K. The keys $K_i$ are called round keys or subkeys and are derived from K using a process called the key schedule.
## Encryption
Given a plaintext block, P, a round function g and round keys $K_1, K_2, . . . ,K_r$
, the ciphertext block, C, is derived through r rounds as follows.
$$
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W_r = g(W_{r−1}, K_r)
C = W_r
$$