Hybrid Cryptography: The Recommended Strategy for Early PQC Adoption

Introduction

The National Institute of Standards and Technology (NIST) has recently finalized the selection of the first four quantum-resistant key encapsulation mechanisms (KEMs) for post-quantum cryptography (PQC). The chosen KEMs, including Kyber, FrodoKEM, and New Hope, are considered to be secure against both classical and quantum computers. However, the transition to these new algorithms is not without its challenges. In this post, we will discuss the recommended strategy for early PQC adoption, which involves using hybrid cryptography to mitigate the risk of unforeseen flaws in newly standardized PQC schemes.

The Need for Hybrid Cryptography

Hybrid cryptography is not a new concept, and it has been widely used in the past to transition from one cryptographic algorithm to another. The main idea behind hybrid cryptography is to use a combination of two or more cryptographic algorithms to provide a higher level of security. In the context of PQC, hybrid cryptography involves running the new PQC algorithm in parallel with an established pre-quantum scheme.

The main advantage of hybrid cryptography is that it provides a higher level of security than using a single algorithm. If one algorithm is compromised or found to have a flaw, the other algorithm can still provide a secure connection. This is particularly important in the context of PQC, where the security of the new algorithms has not been extensively tested and validated.

Theoretical Background

In a hybrid PQC system, the new PQC algorithm is used to generate a shared secret key, which is then used to encrypt the data using an established pre-quantum scheme. The main idea behind this approach is to leverage the computational hardness of both the PQC algorithm and the pre-quantum scheme to provide a secure connection.

The PQC algorithm is used to generate a shared secret key, which is then used to encrypt the data using an established pre-quantum scheme.

Kyber Algorithm

One of the most widely used PQC algorithms is Kyber, which is a lattice-based KEM. Kyber uses a hybrid approach to generate a shared secret key, which is then used to encrypt the data using an established pre-quantum scheme.

Kyber is based on the hardness of the Short Integer Solution (SIS) problem, which is the problem of finding a short vector in a lattice that is close to a given target vector. The SIS problem is considered to be quantum-resistant, and it has been shown to be secure against both classical and quantum computers.

Elliptic-Curve Diffie-Hellman

Elliptic-curve Diffie-Hellman (ECDH) is a widely used pre-quantum scheme that is based on the hardness of the elliptic curve discrete logarithm problem. ECDH is a key agreement protocol that allows two parties to establish a shared secret key over an insecure channel.

ECDH is based on the hardness of the elliptic curve discrete logarithm problem, which is the problem of finding the discrete logarithm of a point on an elliptic curve given a base point and a target point. The elliptic curve discrete logarithm problem is considered to be classical-resistant, and it has been widely used in various cryptographic applications.

Practical Applications

Hybrid PQC systems can be used in various practical applications, including secure communication protocols, digital signatures, and key exchange protocols. In the context of secure communication protocols, hybrid PQC systems can be used to provide secure communication between two parties over an insecure channel.

Code Example

Here is an example of how a hybrid PQC system can be implemented using the Kyber and ECDH algorithms:

// Generate a shared secret key using the Kyber algorithm
shared_secret_key = kyber_key_agreement(public_key_A, public_key_B)

// Encrypt the data using the ECDH algorithm
encrypted_data = ecdh_encrypt(shared_secret_key, data)

// Decrypt the data using the ECDH algorithm
decrypted_data = ecdh_decrypt(shared_secret_key, encrypted_data)

Security Implications and Best Practices

When implementing a hybrid PQC system, it is important to consider the security implications and best practices. Some of the key security considerations include:

Key management: Hybrid PQC systems require careful key management, including key generation, distribution, and revocation.
Algorithm selection: The selection of the PQC algorithm and the pre-quantum scheme should be based on a thorough analysis of the security requirements and the potential risks.
Implementation security: The implementation of the hybrid PQC system should be secure and free from vulnerabilities, including buffer overflows and side-channel attacks.

By following these best practices and security considerations, hybrid PQC systems can provide a high level of security and resilience against both classical and quantum computers.

Conclusion

Hybrid cryptography is a recommended strategy for early PQC adoption, as it provides a higher level of security than using a single algorithm. By combining the computational hardness of the PQC algorithm and the pre-quantum scheme, hybrid PQC systems can provide a secure connection even if one of the algorithms is compromised or found to have a flaw. In this post, we have discussed the theoretical background and practical applications of hybrid PQC systems, as well as the security implications and best practices.