Cryptography Notes

Cryptography

Early Applications and Examples

Cryptography revolves around the protection and preservation of information. Its goals have remained consistent throughout its evolution, although the tools have changed. The field primarily focuses on:

  • Encryption: The process of scrambling information to protect it.

  • Cryptanalysis: The study of decoding or revealing concealed data.

History of Cryptography

  • Ancient Egyptian hieroglyphics served as one of the earliest forms of cryptography.

  • The hieroglyphs were not merely for secrecy but rather provided a unique means of communication with deities and eternity.

  • Knowledge of this system was likely restricted to the royal family and certain religious Orders.

  • Over time, as the complexity of the writing increased, it became inaccessible, and the understanding was lost until rediscovery.

The Rosetta Stone

  • The Rosetta Stone was instrumental in deciphering Egyptian hieroglyphics, taking over 20 years to fully comprehend its significance and the language it represented.

Tracing the Evolution of Cryptography

  • Modern applications of cryptography focus on safeguarding communication between parties.

  • Along with confidentiality, today’s cryptography emphasizes detecting unauthorized modifications to information.

Goals of Modern Cryptography

Cryptography serves multiple objectives:

  1. Confidentiality: The primary aim is to keep information secret from unauthorized access.

  2. Integrity: It ensures that information remains unchanged and validates its authenticity.

  3. Authentication: Confirms the identity of a party involved in the communication.

  4. Nonrepudiation: Guarantees that an entity cannot deny the validity of a contract or agreement.

  5. Key Distribution: Involves the secure sharing of keys, which are vital for encryption processes.

How Cryptography Works

Plaintext and Ciphertext

  • Plaintext: The original message, readable and unaltered.

  • Ciphertext: The encoded version of the plaintext, created using an algorithm and a key, which can be reversed back to plaintext.

  • Algorithms: A defined set of steps to transform plaintext into ciphertext and vice versa.

  • Keys: Unique pieces of information used in cryptographic operations, similar to physical keys that unlock specific constraints.

Types of Cryptography

  • Symmetric Cryptography: Uses the same key for both encryption and decryption, requiring that the key remains secret.

  • Asymmetric (Public-Key) Cryptography: Utilizes a pair of keys (public and private). The public key can be shared, but the private key must remain confidential. This system addresses key management issues faced by symmetric systems and enhances security against eavesdropping.

Digital Signature

  • Public-key cryptography enables the creation of digital signatures, confirming the identity of the user who encrypts a message. Encryption with a private key can only be decrypted with the corresponding public key, ensuring that the origin of the message is verifiable.

Hashing

  • Hashing is a one-way encryption process creating a fixed-length output (hash value or message digest) from input data, used primarily to validate data integrity.

  • The length of the output is consistent, regardless of input size, which aids in detecting any changes.

Issues with Cryptography

  • Cryptographic systems face threats such as brute-force attacks, where every possible key combination is attempted to gain unauthorized access.