SSCP Systems Security Certified PractitionerCryptographyMedium
A system uses a custom block cipher in Electronic Codebook (ECB) mode to encrypt sensitive image files. A security audit reveals that while the encryption works, distinct patterns from the original image are still visible in the encrypted output. What is the fundamental reason for this vulnerability?
- AECB mode encrypts identical plaintext blocks into identical ciphertext blocks
- BLack of a strong key derivation function
- CInsufficient key length of the block cipher
- DThe absence of a digital certificate for key exchange
Show answer & explanationAnswer & explanation
Correct answer: A. ECB mode encrypts identical plaintext blocks into identical ciphertext blocks
Electronic Codebook (ECB) mode encrypts each block of plaintext independently. If two plaintext blocks are identical, they will produce identical ciphertext blocks. In images, areas of uniform color or repeating patterns will result in repeating ciphertext blocks, revealing patterns in the encrypted output, thereby compromising confidentiality.
Why the other options are wrong
- B. Key derivation functions relate to key strength from passwords, not the block cipher mode's behavior.
- C. Insufficient key length would make the cipher vulnerable to brute-force attacks, but wouldn't inherently cause pattern visibility in ECB mode.
- D. Digital certificates are for authentication and key exchange in asymmetric cryptography, unrelated to the internal workings of a symmetric block cipher mode.
ECB Mode Vulnerability
The vulnerability of Electronic Codebook (ECB) mode where identical plaintext blocks are encrypted into identical ciphertext blocks, revealing patterns in the encrypted data and compromising confidentiality.
- Encrypts each block independently.
- No chaining or initialization vector (IV).
- Suitable only for very short, random data (e.g., encrypting other keys).
Memory trick: ECB Repeats, CBC Chains.