The RDRAND instruction, part of Intel's Digital Random Number Generator (DRNG), enhances the security of OpenSSL's random number generation by providing a hardware-based source of cryptographically secure random numbers. Here's how it contributes to security:
1. Hardware-Based Entropy: RDRAND generates truly random numbers directly from hardware, leveraging thermal noise within the CPU. This is more secure than software-based pseudorandom number generators (PRNGs), which can be predictable if not properly seeded with high-quality entropy.
2. Reduced Dependence on OS Entropy Pool: When RDRAND is used, OpenSSL does not need to rely on the operating system's entropy pool for random number generation. This reduces the risk associated with potential weaknesses in the OS's entropy collection mechanisms, such as insufficient entropy or predictability issues.
3. Compliance with Security Standards: RDRAND is designed to meet security standards like NIST SP800-90, FIPS 140-2, and ANSI X9.82, making it suitable for applications requiring high security compliance. This ensures that cryptographic protocols using RDRAND for key generation or session values meet rigorous security requirements.
4. Enhanced Cryptographic Robustness: By using RDRAND, cryptographic protocols can avoid weaknesses associated with poor key generation methods, such as those seen in past incidents like the Debian/OpenSSL fiasco. High-quality random numbers are crucial for preventing attacks that exploit weak keys.
5. Direct Integration with OpenSSL: OpenSSL supports RDRAND through its ENGINE API, allowing applications to use RDRAND directly for random number generation. This integration simplifies the process of leveraging hardware-based randomness in cryptographic applications.
However, there are also considerations regarding the use of RDRAND. Some users might be concerned about potential backdoors in Intel's hardware, although there is no concrete evidence to support these claims. Additionally, if RDRAND is used as the sole source of randomness, it might not be suitable for all scenarios, especially those requiring additional entropy sources for enhanced security.
To manage these concerns, OpenSSL provides options to control the use of RDRAND. Developers can explicitly disable RDRAND or use it in conjunction with other entropy sources to ensure a robust random number generation process. This flexibility allows applications to balance security needs with potential risks associated with relying solely on hardware-based random number generation.
Citations:
[1] https://forum.netgate.com/topic/78574/question-on-hardware-crypto-support-rdrand-only-source-question-to-devs
[2] https://wiki.openssl.org/index.php/Library_Initialization
[3] https://security.stackexchange.com/questions/47598/why-openssl-cant-use-dev-random-directly
[4] https://wiki.openssl.org/index.php/Random_Numbers
[5] https://www.intel.com/content/www/us/en/developer/articles/guide/intel-digital-random-number-generator-drng-software-implementation-guide.html
[6] https://encyclopedia.pub/entry/33752
[7] https://github.com/google/differential-privacy/issues/12
[8] https://ostif.org/our-review-of-the-openssl-1-1-1-random-number-generation-update/
[9] https://security.stackexchange.com/questions/168721/is-it-still-secure-if-a-cryptographic-key-generated-with-openssl-while-a-backdoo
[10] https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/best-practices/srbds-mitigation-impact-intel-secure-key.html