Secure Shell (SSH) is a widely used cryptographic protocol that establishes secure and encrypted communication over potentially untrusted networks, primarily supporting remote login and command-line execution. The SSH Transport Layer Protocol relies on the classical Elliptic Curve Diffie-Hellman (ECDH) key exchange mechanism, which derives its security from the computational hardness of the Elliptic Curve Discrete Logarithm Problem (ECDLP). However, with the emergence of quantum computing, the ECDLP can be solved efficiently, making traditional SSH protocols vulnerable to quantum attacks. To mitigate this threat, several approaches combining classical and post-quantum cryptographic techniques have been proposed; however, security analyses have revealed vulnerabilities to critical attacks. In response, we propose a post-quantum key exchange protocol for SSH, utilising the Split-Key Encapsulation Mechanism (KEM). The key generated through this protocol can then be used for subsequent communication tasks, such as authentication. The security of the proposed protocol is formally validated using the Real-Or-Random (ROR) model and the Scyther tool. Furthermore, we perform a comparative evaluation in terms of computational and communication costs to assess execution time and conduct a testbed analysis, demonstrating that the proposed scheme can be efficiently implemented in real-world applications. The comparative analysis reveals that the designed post-quantum secure protocol reduces computational cost by up to 98% compared to its competitors.
Secure Shell (SSH) is a widely used cryptographic protocol that establishes secure and encrypted communication over potentially untrusted networks, primarily supporting remote login and command-line execution. The SSH Transport Layer Protocol relies on the classical Elliptic Curve Diffie-Hellman (ECDH) key exchange mechanism, which derives its security from the computational hardness of the Elliptic Curve Discrete Logarithm Problem (ECDLP). However, with the emergence of quantum computing, the ECDLP can be solved efficiently, making traditional SSH protocols vulnerable to quantum attacks. To mitigate this threat, several approaches combining classical and post-quantum cryptographic techniques have been proposed; however, security analyses have revealed vulnerabilities to critical attacks. In response, we propose a post-quantum key exchange protocol for SSH, utilising the Split-Key Encapsulation Mechanism (KEM). The key generated through this protocol can then be used for subsequent communication tasks, such as authentication. The security of the proposed protocol is formally validated using the Real-Or-Random (ROR) model and the Scyther tool. Furthermore, we perform a comparative evaluation in terms of computational and communication costs to assess execution time and conduct a testbed analysis, demonstrating that the proposed scheme can be efficiently implemented in real-world applications. The comparative analysis reveals that the designed post-quantum secure protocol reduces computational cost by up to 98% compared to its competitors.
Abstract - In the emerging era of quantum computing, traditional cryptographic algorithms such as RSA and Elliptic Curve Cryptography (ECC) are at risk from quantum-based attacks. These developments pose a significant threat to secure network communication systems that rely on classical key exchange mechanisms. To overcome this challenge, the proposed work introduces a Hybrid Quantum-Resistant Key Exchange Protocol that combines the strengths of both classical andpost-quantum cryptographic algorithms. The hybrid approach integrates Elliptic Curve Dif ie–Hellman (ECDH) with alattice-based post-quantum algorithm, Kyber, to establish a shared session key between communicating entities. This sharedkeyisthen utilized for symmetric encryption using AES to ensure confidentiality and data integrity. The system is implementedusingPython socket programming to demonstrate secure data transmission between client and server. Performance is analyzedinterms of key generation time, encryption and decryption speed, key size, and computational ef iciency. The results validatethatthe proposed hybrid model provides enhanced resistance against quantum attacks while maintaining acceptable performance, making it suitable for future secure communication systems. Keywords - elliptic curve dif ie–hellman, hybrid key exchange, kyber, post-quantum cryptography, quantum computing.
The Secure Shell (SSH) protocol is one of the first security protocols on the Internet to upgrade itself to resist attacks against future quantum computers, with the default adoption of the “quantum (otherwise, classically)” secure hybrid key exchange in OpenSSH from April 2022. However, there is a lack of a comprehensive security analysis of this quantum-resistant version of SSH in the literature: related works either focus on the hybrid key exchange in isolation and do not consider security of the overall protocol, or analyze the protocol in security models which are not appropriate for SSH, especially in the “post-quantum” setting. In this paper, we remedy the state of affairs by providing a thorough post-quantum cryptographic analysis of SSH. We follow a “top-down” approach wherein we first prove security of SSH in a more appropriate model, namely, our post-quantum extension of the so-called authenticated and confidential channel establishment (ACCE) protocol security model; our extension which captures “harvest now, decrypt later” attacks could be of independent interest. Then we establish the cryptographic properties of SSH's underlying primitives, as concretely instantiated in practice, based on our protocol-level ACCE security analysis: for example, we prove relevant cryptographic properties of “Streamlined NTRU Prime”, a key encapsulation mechanism (KEM) which is used in recent versions of OpenSSH and TinySSH, in the quantum random oracle model, and address open problems related to its analysis in the literature. Notably, our ACCE security analysis of post-quantum SSH relies on the weaker notion of IND-CPA security of the ephemeral KEMs used in the hybrid key exchange. This is in contrast to prior works which rely on the stronger assumption of IND-CCA secure ephemeral KEMs. Hence we conclude the paper with a discussion on potentially replacing IND-CCA secure KEMs in current post-quantum implementations of SSH with simpler and faster IND-CPA secure counterparts, and also provide the corresponding benchmarks.
Widely used communication and messaging protocols, e.g., TLS 1.3 and Signal, are insecure against an adversary with a quantum computer. We expect that post-quantum security will become mandatory for a new generation of cryptographic protocols in the nearest 10-15 years. The analysis of existing post-quantum secure cryptographic tools for key exchange, encryption and message authentication based on hard problems in codes, lattices, ring learning with errors and elliptic curve isogenies revealed their advantages and drawbacks. In particular, we conclude, that the main threat to communication and messaging protocols is only pre-quantum security of currently used Diffie-Hellman key exchange protocols. We summarize efficiency and safety results for each class of post-quantum cryptographic schemes and present an experimental implementation of isogeny-based Diffie-Hellman-like key exchange protocol as an illustration of their applicability.
Quantum computing threatens classical key exchange protocols such as Elliptic Curve Diffie–Hellman (ECDH). Post-quantum schemes like Supersingular Isogeny Diffie–Hellman (SIDH) offer quantum resistance but at notable computational and communication costs. We propose DualSecure Key Exchange (DSKE), a hybrid protocol that integrates the classical security of ECDH with the quantum resistance of SIDH. Methodology: DSKE jointly derives two shared secrets -KECDH via elliptic-curve scalar multiplication over a 256-bit prime field and KSIDHvia supersingular isogeny mappings—then fuses them using a secure KDF (e.g., SHA-3): K=KDF(KECDH || KSIDH). We formalize core operations and asymptotics (ECDH O(n3); SIDH O(mlog m)), specify key materials, and fix parameter choices aligned with established baselines (e.g., Curve25519 for ECDH and standard SIKE/SIDH parameter sets) to ensure reproducibility. Experimental settings: Evaluations were conducted on an Intel Core i7 with 16 GB RAM using Python-based cryptographic libraries, with repeated trials for timing stability. Results: DSKE achieves runtime = 6.6 ms versus ECDH = 1.2 ms and SIDH = 5.4 ms; communication = 512 bytes versus ECDH = 128 bytes and SIDH = 384 bytes; and key size 1024 bits (hybrid) versus 256 bits (ECDH) and 768 bits (SIDH). Comparative analysis against SIKE further contextualizes DSKE’s efficiency–security trade-off. Security strength follows the minimum of the constituent levels; with a 256-bit prime for ECDH (=128-bit classical) and standard SIDH/SIKE parameters (targeting =128-bit quantum), the fused key maintains an effective 128-bit level under the stated assumptions and KDF construction. These results indicate that DSKE offers a balanced pathway toward post-quantum readiness, particularly for long-lived, security-critical deployments that can tolerate modest overheads for dual-layer protection.
The advancement of quantum computing poses a significant threat to classical cryptographic algorithms, particularly those based on factorization and discrete logarithm problems. In this paper, we propose a secure and quantum-resistant key exchange scheme leveraging the FrodoKEM algorithm, a lattice-based post-quantum key encapsulation mechanism designed to resist attacks from quantum adversaries. FrodoKEM, being based on the Learning with Errors (LWE) problem, offers a conservative and standard approach to post-quantum cryptography without relying on structured lattices. We compare the performance and security of the proposed scheme against traditional key exchange mechanisms such as RSA and Elliptic Curve Diffie-Hellman (ECDH), as well as other post-quantum algorithms like Kyber and NTRU. Our analysis demonstrates that FrodoKEM offers improved security assurances and competitive performance metrics, especially in environments where long-term confidentiality and forward secrecy are critical. The experimental results affirm FrodoKEM's suitability for real-world deployment in post-quantum secure communications.
The migration of remote-access and industrial communication systems from classical public-key cryptography to post-quantum cryptography (PQC) requires careful evaluation at both the protocol and system levels. This paper presents PQC-E2E-CA, a system-level evaluation framework for reviewing post-quantum and hybrid cryptographic configurations in Secure Shell (SSH). The framework integrates OQS-enabled OpenSSH and OpenSSL with Linux netem network emulation, automated experiment execution, SCP integrity verification, and statistical post-processing. The evaluation separates key exchange behavior from host key authentication. Specifically, it measures ML-KEM and hybrid ML-KEM as SSH key exchange mechanisms, and ML-DSA as a host-key signature mechanism. Experiments are conducted under controlled RTT and packet-loss conditions using a gateway virtualised client-server testbed. The results show that ML-KEM and hybrid ML-KEM can be integrated into SSH without prohibitive application-level session setup overhead in the evaluated environment. Among the evaluated configurations, ML-KEM-768 demonstrates comparatively lower SSH session establishment latency at 50 ms RTT with 0% packet loss. ML-DSA-44 achieves the lowest host-key authentication latency under the same conditions and maintains relatively stable performance at 150 ms RTT with 5% packet loss. SCP throughput results for 100 MB and 200 MB transfers indicate that sustained transfer performance is mainly influenced by RTT and transport-layer dynamics using a single dominant key exchange configuration. These findings support migration toward standardized post-quantum mechanisms in SSH-based gateway and remote-access environments, provided that algorithm choice and system configuration are validated under representative workloads and network conditions.