Understanding How PKI Certificates Power Encryption: A Technical Exploration

This article is the second of three, in which I describe the future of PKI, and the inherent trust we place in companies and individuals that we have no relationship with all aspects of our digital lives.

Public Key Infrastructure (PKI) plays a crucial role in securing communications over the internet, providing the foundation for encryption protocols like SSL/TLS that protect data in transit. For those in technical roles who are not cryptographers, understanding how PKI certificates are used in encryption is essential. This article will explore the fundamentals of symmetric and asymmetric encryption, the role of RSA and Diffie-Hellman in PKI, the evolution of SSL/TLS, vulnerabilities inherent in these protocols, and the emerging challenges posed by quantum computing.

Symmetric vs Asymmetric Encryption

Encryption can broadly be classified into two categories: symmetric and asymmetric.

• Symmetric encryption uses a single key for both encryption and decryption. This method is fast and efficient, making it ideal for encrypting large amounts of data. However, the challenge lies in securely sharing the key between parties, as both must have access to the same key.
• Asymmetric encryption solves this problem by using a pair of keys: a public and private key, which are mathematically linked. The private key holder can decrypt the data encrypted with the public key, ensuring secure communication even if the public key is widely distributed. The trade-off is that this asymmetric encryption is computationally more intensive than symmetric encryption.

The Role of RSA and Diffie-Hellman in PKI

Two fundamental algorithms underpin asymmetric encryption in PKI: RSA and Diffie-Hellman.

• RSA (Rivest-Shamir-Adleman) is based on the mathematical challenge of factoring large prime numbers. Factoring, in this context, refers to finding two prime numbers that multiply together to form a given large number. The security of RSA relies on the fact that while it is easy to multiply two large primes, it is computationally infeasible to reverse the process—i.e., to factor the product back into its prime components without knowing them in advance. This principle ensures that the private key, derived from these prime factors, remains secure.
• Diffie-Hellman is another cornerstone of cryptographic protocols, enabling two parties to establish a shared secret over an insecure channel. Unlike RSA, which is used for encryption and digital signatures, Diffie-Hellman is primarily used for securely exchanging cryptographic keys. This key exchange protocol leverages the difficulty of solving discrete logarithm problems, ensuring that the shared key remains secret even if the exchange is observed.

In PKI, asymmetric encryption is often used to securely exchange a symmetric key, which is then used to encrypt the actual data. This hybrid approach leverages the strengths of both encryption types: the security of asymmetric encryption and the efficiency of symmetric encryption.? A compromise of the asymmetric encryption will result in the compromise of the symmetric encryption.

The Evolution of SSL/TLS

Secure Sockets Layer (SSL) and its successor, Transport Layer Security (TLS), are the protocols that implement encryption over the internet. They provide the security backbone for HTTPS, ensuring that data transmitted between a web server and a client remains confidential and tamper-proof.

• SSL 1.0 was never released publicly due to security flaws.
• SSL 2.0 (1995) was the first public release but was quickly found to have significant vulnerabilities, such as susceptibility to man-in-the-middle attacks.
• SSL 3.0 (1996) addressed many of these issues but introduced new vulnerabilities, such as the POODLE attack, which exploited weaknesses in SSL 3.0’s fallback mechanism to force clients to use weaker encryption.
• TLS 1.0 (1999) was developed as a more secure replacement for SSL, but it too had vulnerabilities, such as the BEAST attack, which exploited weaknesses in the CBC (Cipher Block Chaining) mode.
• TLS 1.2 (2008) and TLS 1.3 (2018) have progressively improved security by deprecating outdated cryptographic algorithms and introducing features like Perfect Forward Secrecy (PFS), which ensures that even if a private key is compromised, past communications remain secure.

Despite these advancements, no protocol is entirely immune to vulnerabilities, particularly as computing power increases and new attack vectors are discovered.

The Mathematics of Asymmetric Encryption: Prime Factorisation

At the heart of RSA’s security is the difficulty of prime factorisation. Prime numbers are integers greater than 1 that have no divisors other than 1 and themselves. The RSA algorithm leverages the fact that, while it is straightforward to multiply two large prime numbers, it is exponentially harder to factor the resulting product back into its original primes. This asymmetry in difficulty underpins the security of RSA, as there is no known efficient algorithm for prime factorisation—a problem that remains unsolved in mathematics.

Side-Channel Attacks: Beyond Mathematical Security

Even if an encryption algorithm is mathematically sound, it can still be vulnerable to side-channel attacks. These attacks exploit physical or implementation weaknesses rather than attempting to break the encryption directly.

• Electromagnetic (EMF) attacks involve monitoring the electromagnetic emissions from a device as it processes cryptographic operations, potentially revealing the secret key.
• Speculative execution attacks, such as Spectre and Meltdown, exploit the way modern processors execute instructions out of order to leak sensitive information.
• Reverse engineering involves analysing the hardware or software implementation of a cryptographic system to discover vulnerabilities.
• Forensic artifact analysis examines the remnants of data left in a system after cryptographic operations, which may provide clues to the secret keys or decrypted data.

The Quantum Computing Threat

Quantum computing represents a paradigm shift in computing power, capable of solving complex problems exponentially faster than classical computers. One such problem is prime factorisation, which RSA relies on for security. Shor’s algorithm, a quantum algorithm, could theoretically factor large numbers in polynomial time, rendering RSA and similar encryption methods obsolete.

While true quantum computers capable of breaking RSA are not yet a reality, experts believe we are on the cusp of a breakthrough. Some estimates suggest that within the next 10 to 20 years, quantum computing could become feasible for business applications. The December 2023 Microsoft breach, while ultimately not attributed to quantum computing, highlighted the industry's concerns about how close we are to such a breakthrough, as it was legitimately considered as the root cause in this major security incident.

The NSA and RSA: Historical Context

There is evidence to suggest that the NSA may have influenced the design of certain cryptographic algorithms, including RSA, potentially inserting backdoors or weakening them. Documents leaked by Edward Snowden revealed that the NSA had actively worked to undermine global encryption standards, raising concerns about the integrity of widely used algorithms.

The Need for Quantum-Resistant Algorithms

Given the potential of quantum computing to break current encryption methods, adversaries are already capturing and storing encrypted communications with the expectation that they can decrypt them in the future. This highlights the urgent need to develop and adopt quantum-resistant algorithms, even though the quantum threat has not yet materialised. Organisations must start planning now to ensure that their data remains secure in a post-quantum world.

Conclusion

PKI and the encryption methods it supports are fundamental to the security of our digital infrastructure. Understanding the principles behind symmetric and asymmetric encryption, the evolution of SSL/TLS, and the emerging threats posed by quantum computing is crucial for anyone involved in securing communications. As we look to the future, the development and adoption of quantum-resistant algorithms will be essential to maintaining trust and security in our digital world.

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