Cryptography Flashcards
FEATURES OF CRYPTOGRAPHY
Confidentiality: Only the intended recipient can access the information.
Integrity: Data cannot be altered without detection during storage or transit.
Non-repudiation: The sender cannot deny their intent to send the information.
Authentication: The identities of both the sender and recipient are verified, ensuring the origin and destination of the data.
Symmetric Encryption
Uses the same key to encrypt and decrypt messages (e.g., DES, AES, Blowfish, RC4).
Asymmetric Encryption
Each party generates a pair of public and private keys. The public key is shared, while the private key is kept secure (e.g., RSA, Elliptic Curve, DSA).
Substitution
Each character in the message is replaced by another character or symbol.
Transposition
Characters in the message are rearranged without changing their identity.
Caesar Cipher
A shift of 3 is applied to each letter of the plaintext.
Formula:
C=E(P)=P+3
Key-based Cipher
Uses a keyword to control encryption by placing the characters of the key at the beginning of the ciphertext, followed by the rest of the alphabet.
VERNAM CIPHER
A transposition cipher where a number is assigned to each letter of the plaintext and key. The characters are combined numerically, then adjusted to fit the alphabet (mod 26).
BLOCK VS STREAM CIPHERS
Block Cipher: Encrypts fixed-size blocks of data (e.g., DES, AES), with padding added if data is insufficient.
Stream Cipher: Encrypts data in real time (e.g., VoIP), using substitution techniques for faster encryption (e.g., RC4).
CONFUSION VS DIFFUSION
Confusion: Complex relationships between ciphertext and key. It makes it hard to find the key even if multiple plaintext-ciphertext pairs are available.
Diffusion: Distributes the plaintext’s statistical structure across the ciphertext. A single change in plaintext results in a drastic change in ciphertext.
