Applied Cryptography Overview

Utilizes a pair of keys: a public key for encryption and a private key for decryption.
Enables secure key exchange and digital signatures.
Examples include RSA, DSA, and ECC (Elliptic Curve Cryptography).

Converts input data of any size into a fixed-size string (hash).
Properties:
- Deterministic: same input yields the same output.
- Fast computation.
- Pre-image resistance: difficult to reverse-engineer the input from the hash.
- Collision resistance: hard to find two different inputs that produce the same hash.
Common hash functions: SHA-256, SHA-3, MD5 (though MD5 is considered weak).

Symmetric encryption algorithm adopted by the U.S. government.
Key sizes: 128, 192, or 256 bits.
Block size: 128 bits.
Based on the substitution-permutation network design; highly secure and efficient.

Symmetric key algorithm that operates on 64-bit blocks with a 56-bit key.
Uses a Feistel network structure.
Considered insecure for modern applications due to small key size and vulnerabilities.

A symmetric encryption method using a single-use, randomly generated key that is as long as the message.
Provides perfect secrecy if used correctly.
Key must be securely shared and truly random; impractical for most applications due to key management challenges.

A concept in cryptography where encryption yields no information about the plaintext without the key.
Achievable with the One Time Pad.
Implies that the ciphertext can be generated from any plaintext, given a corresponding key.

The study of techniques for breaking encryption and discovering plaintext from ciphertext.
Types include:
- Brute force attack: tries all possible keys.
- Frequency analysis: analyzes the frequency of letters or patterns in the ciphertext.
- Known-plaintext attack: uses known pairs of plaintext and ciphertext to find the key.
Ongoing research to enhance cryptographic security against evolving threats.

Involves a single key for both encryption and decryption, emphasizing the importance of key management.
If the encryption key is compromised, the system's security is at risk.
Prominent algorithms include AES (Advanced Encryption Standard), DES (Data Encryption Standard), and RC4.

Relies on a key pair: a public key for encryption and a private key for decryption.
Facilitates secure key exchanges and the creation of digital signatures.
Notable examples are RSA (Rivest-Shamir-Adleman), DSA (Digital Signature Algorithm), and ECC (Elliptic Curve Cryptography).

Transforms input data of any size into a fixed-length string known as a hash.
Characteristics include:
- Deterministic behavior: identical input results in the same hash output.
- Quick computation process.
- Pre-image resistance: challenging to reverse-engineer the original input from the hash.
- Collision resistance: difficult to find two different inputs yielding the same hash.
Frequently used hash functions include SHA-256 and SHA-3, while MD5 is considered obsolete due to vulnerabilities.

Symmetric encryption standard recognized and adopted by the U.S. government.
Offers key sizes of 128, 192, or 256 bits with a consistent block size of 128 bits.
Employs a substitution-permutation network design, achieving high levels of security and efficiency.

Operates on 64-bit data blocks using a 56-bit key.
Utilizes a Feistel network structure for encryption.
No longer considered secure for contemporary applications due to its short key length and known vulnerabilities.

Employs a symmetric encryption method that uses a randomly generated key matching the length of the message.
Guarantees perfect secrecy if the key is securely shared and truly random.
Challenges include impracticality for most applications due to the complexity of key management.

A theoretical concept whereby encryption provides no insight into the plaintext without knowledge of the key.
Attainable through the One Time Pad method, where ciphertext could correspond to any plaintext given the correct key.

Analyzes methods for breaking encryption and retrieving plaintext from encrypted data (ciphertext).
Various techniques include:
- Brute force attacks: testing every possible key to unlock encrypted data.
- Frequency analysis: examining letter or pattern frequencies in ciphertext to deduce information.
- Known-plaintext attacks: leveraging pairs of known plaintext and ciphertext to derive the encryption key.
Continued research aims to strengthen cryptographic methods against advancing threats.