Week 1

Symmetric Encryption

Symmetric Encryption

• Definition: A type of encryption where the same key is used for both encryption and decryption.

• Pros:

  • Faster than asymmetric encryption.

  • Suitable for encrypting large amounts of data.

• Cons:

  • Key distribution can be challenging.

  • If the key is compromised, the security is broken.

Asymmetric Encryption

• Definition: A type of encryption that uses a pair of keys – a public key for encryption and a private key for decryption.

• Pros:

  • Solves the key distribution problem.

  • Provides digital signatures for authentication.

• Cons:

  • Slower than symmetric encryption.

  • Requires more computational resources.

Confidentiality

Definition: Ensuring that information is accessible only to those authorized to have access.

Integrity

Definition: Ensuring that data is accurate and has not been tampered with.

Availability

Definition: Ensuring that authorized users have access to information and resources when needed

Breach of Security Levels of Impact

Definition: The severity of the consequences resulting from a security breach, ranging from low to high impact

Active Attacks

Definition: Attempts to alter system resources or affect their operation (e.g., modification of messages, replay attacks)

Passive Attacks

Definition: Attempts to learn or make use of information from the system but do not affect system resources (e.g., eavesdropping).

Nonrepudiation

Definition: Assurance that someone cannot deny the validity of their signature on a document or a message that they originated

Plaintext

Definition: The original message or data that is fed into the encryption algorithm

Ciphertext

Definition: The encrypted message produced as output by the encryption algorithm

Substitution

Definition: A cryptographic technique where elements of the plaintext are systematically replaced with other symbols

Transposition

Definition: A cryptographic technique where the positions of elements in the plaintext are shifted according to a regular system

Block Cipher

• Description: Encrypts data in fixed-size blocks (e.g., 64 or 128 bits) using the same key for each block.

• Pros:

  • Strong security due to complex encryption algorithms.

  • Suitable for encrypting large chunks of data.

• Cons:

  • Can be slower due to processing entire blocks.

  • Padding may be required for data not fitting the block size.

Stream Cipher

• Description: Encrypts data one bit or byte at a time using a key stream.

• Pros:

  • Faster than block ciphers for streaming data.

  • No need for padding.

• Cons:

  • More vulnerable to certain types of attacks if the key stream is not properly managed.

  • Typically weaker encryption than block ciphers.

Cryptanalysis

Definition: The study of analyzing information systems to understand hidden aspects of the systems

Brute Force

Definition: A method of breaking encryption by trying all possible keys until the correct one is found

Caesar Cipher

• Description: A substitution cipher where each letter in the plaintext is shifted a certain number of places down or up the alphabet.

• Pros:

  • Simple and easy to understand.

• Cons:

  • Very easy to break with frequency analysis or brute force

Monoalphabetic Cipher

• Description: A substitution cipher where each letter of the plaintext is mapped to a fixed different letter of the alphabet.

• Pros:

  • Slightly more secure than Caesar Cipher.

• Cons:

  • Still vulnerable to frequency analysis

Permutation

• Description: A transposition cipher that rearranges the positions of characters in the plaintext according to a certain system.

• Pros:

  • Can be combined with substitution for increased security.

• Cons:

  • Alone, it provides weak security

Playfair Cipher

• Description: A digraph substitution cipher using a 5x5 matrix of letters to encrypt pairs of letters.

• Pros:

  • More secure than simple substitution ciphers.

• Cons:

  • More complex to use and understand.

  • Still vulnerable to frequency analysis

Hill Cipher

• Description: A polygraphic substitution cipher that uses linear algebra and matrix multiplication to encrypt blocks of text.

• Pros:

  • Stronger than monoalphabetic ciphers.

• Cons:

  • Requires matrix inversion for decryption, which can be complex.

One-Time Pad

• Description: A cipher where the plaintext is combined with a random key that is as long as the plaintext.

• Pros:

  • Provably unbreakable if the key is truly random and used only once.

• Cons:

  • Key distribution and management are impractical for most uses

Rail Fence Cipher

• Description: A transposition cipher that arranges the plaintext in a zigzag pattern and then reads off each row.

• Pros:

  • Simple to implement.

• Cons:

  • Weak security, easy to break with a small number of rows.

Row Transposition Cipher

• Description: A transposition cipher that arranges the plaintext in a rectangle and then permutes the columns according to a key.

• Pros:

  • More secure than the Rail Fence Cipher.

• Cons:

  • Still vulnerable to anagramming attacks if the key is short or simple.

Vigenere Cipher

Description

The Vigenère Cipher is a method of encrypting alphabetic text by using a simple form of polyalphabetic substitution. It employs a keyword to shift the letters of the plaintext. Each letter in the keyword shifts corresponding letters in the plaintext by different amounts, resulting in a more secure cipher than simple substitution.

Pros

• Increased Security: More secure than monoalphabetic ciphers due to multiple Caesar ciphers being applied.

• Simple to Implement: Easy to understand and implement by hand.

Cons

• Vulnerable to Kasiski Examination and Frequency Analysis: Patterns in the keyword can be exploited to break the cipher.

• Keyword Management: The security of the cipher heavily depends on the secrecy of the keyword

Vigenere Cipher Hand Encryption

• Choose a Keyword: Repeat the keyword until it matches the length of the plaintext.

• Convert Letters to Numbers: Assign a number to each letter (A=0, B=1, ..., Z=25).

• Shift Letters: For each letter in the plaintext, shift it by the number corresponding to the keyword letter.

• Convert Numbers Back to Letters: Convert the resulting numbers back to letters.

Vigenere Cipher Hand Decryption

• Repeat the Keyword: As in encryption, match the length of the ciphertext with the repeated keyword.

• Convert Letters to Numbers: Assign numbers to both the ciphertext and the keyword.

• Reverse the Shift: Subtract the keyword number from the ciphertext number for each letter.

• Convert Numbers Back to Letters: Convert the resulting numbers back to letters.