Hybrid plaintext attack for a cryptosystem based on interference and the phase-retrieval technique.

Area of Science:

• Optical security systems
• Cryptography
• Information security

Background:

• Conventional interference-based optical cryptosystems often suffer from silhouette problems.
• Phase-retrieval techniques enhance optical cryptosystems by generating phase-only masks (POMs) as ciphertexts.
• The proposed system utilizes phase retrieval to improve security and potentially mitigate silhouette issues.

Purpose of the Study:

• To evaluate the security strength of an enhanced optical cryptosystem.
• To identify and exploit vulnerabilities in the system's security mechanisms.
• To propose a novel attack strategy against the enhanced cryptosystem.

Main Methods:

• A hybrid known-plaintext attack (KPA) was developed.
• Three known plaintext-ciphertext pairs were used as amplitude and phase constraints.
• The attack aimed to precisely estimate the fixed random phase mask (RPM), the system's private key.

Main Results:

• The study demonstrated that the RPM, despite being fixed, is susceptible to recovery via KPA.
• The proposed hybrid KPA successfully estimated the RPM using limited known plaintext-ciphertext pairs.
• The cryptoanalysis confirmed a security leak, rendering the cryptosystem vulnerable.

Conclusions:

• The enhanced optical cryptosystem, despite using phase retrieval, is vulnerable to the proposed known-plaintext attack.
• The fixed nature of the random phase mask is a critical security flaw.
• Numerical simulations validated the effectiveness of the attack in retrieving plaintext information.