OCR A-level Computer Science: Data Compression, Encryption, and Hashing

Data Compression, Encryption, and Hashing

Data Compression

Data compression is the process of reducing the size of a data file without losing any information (lossless) or losing some information (lossy).

Lossless Compression:

• Retains all original data.
• Suitable for text, code, and images where data integrity is crucial.
• Methods:
  • Run-Length Encoding (RLE): Replaces repeated sequences of data with a count and the data itself. AAAABBBCCCDD -> 4A3B4C2D
  • Dictionary Coding: Replaces frequently occurring patterns with shorter codes. the quick brown fox jumps over the lazy dog can be compressed using a dictionary that maps words to shorter codes.

Lossy Compression:

• Reduces file size by discarding some data.
• Suitable for images, audio, and video where minor quality loss is acceptable.
• Methods:
  • JPEG: Uses quantization to discard less important data from the image.
  • MP3: Removes inaudible frequencies from audio signals.

Benefits of Data Compression:

• Reduced storage space requirements.
• Faster data transmission.
• Efficient use of network bandwidth.

Encryption

Encryption is the process of converting data into an unreadable format (ciphertext) using an algorithm and a key. Only authorized individuals with the correct key can decrypt the data back to its original form (plaintext).

Symmetric Encryption:

• Uses the same key for both encryption and decryption.
• Examples:
  • AES (Advanced Encryption Standard): A widely used symmetric encryption algorithm.
  • DES (Data Encryption Standard): An older symmetric encryption algorithm.

Asymmetric Encryption:

• Uses separate keys for encryption and decryption.
• Public key is used for encryption, while the private key is used for decryption.
• Examples:
  • RSA (Rivest–Shamir–Adleman): A widely used asymmetric encryption algorithm.
  • ECC (Elliptic Curve Cryptography): A more efficient asymmetric encryption algorithm.

Benefits of Encryption:

• Confidentiality: Protects data from unauthorized access.
• Integrity: Ensures data has not been altered during transmission.
• Authentication: Verifies the identity of the sender and receiver.

Hashing

Hashing is a process of generating a fixed-size unique fingerprint (hash value) from a data input. It is a one-way function, meaning it is impossible to reverse the hashing process to retrieve the original data.

Applications of Hashing:

• Data Integrity: Detecting data corruption or modification.
• Password Storage: Storing hashed passwords instead of plain text passwords for security.
• Digital Signatures: Verifying the authenticity and integrity of digital documents.

Properties of Hash Functions:

• Pre-image resistance: Difficult to find the input given the hash value.
• Second pre-image resistance: Difficult to find a different input with the same hash value as a given input.
• Collision resistance: Difficult to find two different inputs with the same hash value.

Common Hashing Algorithms:

• MD5: A widely used but outdated hashing algorithm.
• SHA-256: A more secure and widely used hashing algorithm.

Benefits of Hashing:

• Data integrity: Ensures data has not been tampered with.
• Security: Protects sensitive data like passwords.
• Efficiency: Fast and efficient for data verification.

Conclusion

Data compression, encryption, and hashing are crucial concepts for ensuring data security and efficiency. Understanding these concepts allows for the development of robust and reliable data management systems.