SSCP Systems Security Certified PractitionerCryptographyMedium
A system administrator is configuring a new web server to use HTTPS. They are deciding between using a block cipher in Cipher Block Chaining (CBC) mode or Counter (CTR) mode for data encryption. The primary concern is parallel processing for high throughput while maintaining strong security. Which mode would be most suitable for this requirement?
- ACipher Block Chaining (CBC)
- BCounter (CTR)
- CElectronic Codebook (ECB)
- DOutput Feedback (OFB)
Show answer & explanationAnswer & explanation
Correct answer: B. Counter (CTR)
CTR mode converts a block cipher into a stream cipher, allowing for parallel encryption and decryption of blocks because each block's keystream is generated independently using a unique counter value. This significantly improves throughput for high-performance systems compared to CBC, which requires sequential processing.
Why the other options are wrong
- A. CBC mode requires sequential processing, as each block's encryption depends on the previous ciphertext block, limiting parallelization.
- C. ECB mode is insecure for most applications due to identical plaintext blocks resulting in identical ciphertext blocks.
- D. OFB mode also operates as a stream cipher but generates keystream blocks sequentially, limiting parallel processing of the keystream generation itself.
Block Cipher Modes of Operation
Methods that specify how a block cipher should be applied to encrypt data blocks, influencing properties like security, error propagation, and performance (e.g., parallelization).
- Transform fixed-size blocks of plaintext into ciphertext.
- Different modes offer varying security and performance characteristics.
- Some modes allow for parallel processing, others require sequential.
Memory trick: To speed up encryption, think of counters counting up independently.