This thesis studies CDOC2 or Crypto Digidoc 2, the file transmission format used in the Estonian eID ecosystem and how it can be adapted for post-quantum security. CDOC2 protects file contents with symmetric cryptography and the key material required for decryption is delivered to recipients through public-key mechanisms such as elliptic-curve Diffie-Hellman, RSA-OAEP, Capsule Server workflows, and Shares Server workflows. These classical public-key mechanisms are vulnerable to quantum computers because of Shor’s algorithm. The thesis proposes a post-quantum design that preserves the existing CDOC2 container structure and operational model wherever possible, while replacing vulnerable key establishment with ML-KEM and adding ML-DSA based authorization for container retrieval from server. A prototype implementation was developed and evaluated against validation tests. The results show that a post-quantum variant of CDOC2 can be implemented without redesigning the symmetric payload encryption layer, but several migration issues were found such as increased header and token sizes, server-side authorization changes, and the need for further production level side-channel, interoperability, and certificate-management analysis.
This thesis studies CDOC2 or Crypto Digidoc 2, the file transmission format used in the Estonian eID ecosystem and how it can be adapted for post-quantum security. CDOC2 protects file contents with symmetric cryptography and the key material required for decryption is delivered to recipients through public-key mechanisms such as elliptic-curve Diffie-Hellman, RSA-OAEP, Capsule Server workflows, and Shares Server workflows. These classical public-key mechanisms are vulnerable to quantum computers because of Shor’s algorithm. The thesis proposes a post-quantum design that preserves the existing CDOC2 container structure and operational model wherever possible, while replacing vulnerable key establishment with ML-KEM and adding ML-DSA based authorization for container retrieval from server. A prototype implementation was developed and evaluated against validation tests. The results show that a post-quantum variant of CDOC2 can be implemented without redesigning the symmetric payload encryption layer, but several migration issues were found such as increased header and token sizes, server-side authorization changes, and the need for further production level side-channel, interoperability, and certificate-management analysis.
Large-scale quantum computers threaten the public-key cryptography that protects enterprise data, communications, and digital identity. Shor's algorithm solves integer factorization and discrete logarithms in polynomial time, which would break RSA, Diffie-Hellman, and elliptic-curve schemes once a cryptographically relevant quantum computer exists. The danger is not only future. Adversaries can record encrypted traffic today and decrypt it later, a tactic known as harvest-now-decrypt-later. In August 2024 the U.S. National Institute of Standards and Technology published its first post-quantum standards: FIPS 203 (ML-KEM, derived from CRYSTALS-Kyber), FIPS 204 (ML-DSA, from CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, from SPHINCS+). This paper presents a practical migration framework for enterprises. It reviews the quantum threat and Mosca's inequality for timing the transition, summarizes the new standards with their key and signature sizes, and proposes a five-phase roadmap built on crypto-agility: discovery and inventory, risk prioritization, agility engineering, hybrid deployment, and validation. Performance trade-offs are analyzed using documented parameter sizes and illustrative TLS handshake figures. ML-KEM-768 carries a 1,184-byte public key against 64 bytes for an elliptic-curve key, while SPHINCS+ signatures can exceed 17 kilobytes. The work does not report a real deployment. It consolidates published parameters and field guidance into an actionable plan, and it highlights open challenges in certificate sizing, hardware support, and long-lived embedded systems.
Large-scale quantum computers threaten the public-key cryptography that protects enterprise data, communications, and digital identity. Shor's algorithm solves integer factorization and discrete logarithms in polynomial time, which would break RSA, Diffie-Hellman, and elliptic-curve schemes once a cryptographically relevant quantum computer exists. The danger is not only future. Adversaries can record encrypted traffic today and decrypt it later, a tactic known as harvest-now-decrypt-later. In August 2024 the U.S. National Institute of Standards and Technology published its first post-quantum standards: FIPS 203 (ML-KEM, derived from CRYSTALS-Kyber), FIPS 204 (ML-DSA, from CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, from SPHINCS+). This paper presents a practical migration framework for enterprises. It reviews the quantum threat and Mosca's inequality for timing the transition, summarizes the new standards with their key and signature sizes, and proposes a five-phase roadmap built on crypto-agility: discovery and inventory, risk prioritization, agility engineering, hybrid deployment, and validation. Performance trade-offs are analyzed using documented parameter sizes and illustrative TLS handshake figures. ML-KEM-768 carries a 1,184-byte public key against 64 bytes for an elliptic-curve key, while SPHINCS+ signatures can exceed 17 kilobytes. The work does not report a real deployment. It consolidates published parameters and field guidance into an actionable plan, and it highlights open challenges in certificate sizing, hardware support, and long-lived embedded systems.
Healthcare systems increasingly depend on interoperable electronic health records, picture archiving and communication systems, cloud analytics, remote monitoring, and connected medical devices. These workflows create a long-lived confidentiality problem: clinical, genomic, pediatric, psychiatric, and family-linked data may remain sensitive for decades, whereas the public-key algorithms that protect current transport and identity systems are vulnerable to future cryptographically relevant quantum computers. Shor's algorithm threatens RSA, finite-field Diffie-Hellman, elliptic-curve Diffie-Hellman, and elliptic-curve signatures, while Grover's algorithm reduces the effective security margin of symmetric primitives. This review validates the post-quantum transition pathway for healthcare and distinguishes software-deployable post-quantum cryptography from hardware-specialized quantum key distribution. We summarize the standardized NIST primitives, correct the status of Falcon/FN-DSA as a FIPS 206 algorithm still in development, analyze deployment constraints in Internet of Medical Things environments, and map cryptographic migration to healthcare governance. A staged, hybrid, crypto-agile migration strategy is recommended: prioritize long-confidentiality data, inventory cryptographic dependencies, deploy hybrid key establishment at enterprise gateways, reserve QKD for selected high-value fixed links, and require vendor update pathways for clinical devices.
The fast development of cyber communications, multimedia distribution, remote working have promoted the demand to transmit sensitive information through secure means in both the public and the private networks. The advent of massive quantum computers is rendering traditional cryptographic algorithms like RSA and Elliptic Curve Cryptography (ECC) insecure because they can crack the classical public-key algorithms like the Shor and Grover algorithms. This brings an immediate need of hybrid cryptographic systems, which integrate classical, quantum, and post-quantum algorithms to provide confidentiality, integrity, authentication, and future security beyond the quantum threat horizon.The paper is a proposal of a Hybrid Quantum-Post-Quantum Cryptographic Framework of transmitting files safely. It starts by aggregating files, which is a process to compress several files, images, videos, and multimedia files that users have chosen into one file to minimize redundancy and ease encryption. The AES-256 encrypted file is in GCM mode and provides confidentiality and integrity of the compressed file.The dual-layer mechanism ensures key establishment security. To begin with, Quantum Key Distribution (QKD) based on the protocols of BB84/E91 allows the Sender and the Receiver to generate a Quantum Secret Key (QSK) by exchanging quantum bits in quantum channel. Constant monitoring of the error rate facilitates automatic eavesdropping detection, and guarantees the keys generation is made when the conditions are secure, as well as the safeguarding of interception and man-in-the-middle attacks.A post-quantum layer is provided to ensure long-term security against quantum cryptanalysis, which uses Kyber, a NIST-approved lattice-based Key Encapsulation Mechanism (KEM). The Receiver creates a key pair of Kyber and disseminates the public key to the Sender. By using encapsulation, the Sender gets a PQC ciphertext and a Shared Secret (SS), with decapsulation on the Receiver side giving ensure that only participants of good faith get the same secret value.The hybridization phase consists of combining the QSK of QKD and SS of Kyber with the help of HKDF-SHA256 to obtain a Final Wrap Key (FWK). AES-GCM encrypts the key of file encryption by wrapping it with FWK which allows a secure and authenticated transfer of the key. The Sender sends four messages: encrypted file, Kyber ciphertext, wrapped AES key and the initialisation vector. At Receiver end, FWK is calculated once again with the help of QSK and SS so that the original data can be decrypted with the help of AES key.The suggested framework provides a defense-in-depth solution based on the combination of quantum security, post-quantum resilience and authenticated symmetric encryption. It can be analyzed that there is a strong resistance to classical and quantum adversaries, scalability, and compatibility with the existing communication networks. This renders the model to be appropriate to secure government communication, military systems, data exchange in healthcare environments, cloud storage and financial infrastructures. Keywords— Quantum Key Distribution (QKD), Post-Quantum Cryptography (PQC), Kyber,Key Encapsulation Mechanism (KEM), HKDF-SHA256, Quantum Secret Key (QSK), GCM Mode.
Advancements in quantum computing create substantial risks for classical cryptographic systems, particularly RSA and Elliptic-Curve Cryptography, that underpin FIDO2 and WebAuthn authentication protocols. Shor's algorithm can compromise these systems by extracting private keys from their public counterparts when sufficiently powerful quantum computers exist. Passwordless authentication has grown increasingly prevalent, with FIDO2 and WebAuthn serving as core trust elements within digital identity architectures. Quantum-enabled attackers present serious challenges to both credential security and attestation validation processes. Organizations must adopt post-quantum cryptographic methods proactively to sustain authentication integrity while maintaining existing trust structures. The harvest-now-decrypt-later paradigm presents urgent risks where malicious entities intercept and store authentication traffic for future decryption upon quantum computer maturation. FIDO2 credentials embedded within authenticators or bound to user devices maintain long lifespans, often synchronized across cloud ecosystems as passkeys, creating extended vulnerability windows. Post-quantum migration represents both cryptographic enhancement and essential lifecycle management spanning authenticators, browsers, servers, and attestation authorities. This framework proposes a crypto-agile hybrid WebAuthn architecture integrating classical and post-quantum algorithms. Embedding ML-DSA for digital signatures and ML-KEM for key encapsulation within WebAuthn registration and authentication flows enables progressive credential rotation without disrupting trust chains. The architecture aligns with CBOR Object Signing and Encryption identifiers and emerging IETF post-quantum WebAuthn specifications, ensuring standards compliance.
Quantum computing is developing quickly, and that's a big problem for traditional encryption techniques such as RSA and elliptic curve cryptography. Shor's algorithm, a quantum algorithm, specifically calls into question the long-term security that Public Key Infrastructures (PKIs) currently rely on. So, this thesis investigates how new post-quantum cryptography methods can be integrated into the public key infrastructure that businesses already use. This thesis examines the problems, both theoretical and practical, that arise when switching to cryptography resistant to quantum attacks. This thesis specifically examines how the NIST-selected algorithms, Kyber and Dilithium, are used in hybrid X.509 certificates that combine classical and post-quantum signatures.A test PKI environment was set up using OpenSSL-OQS and OpenXPKI to facilitate the testing process. Important PKI processes were examined in this setting, including TLS handshakes, certificate issuance, validation, and revocation. The results show that integrating PQC increases key and certificate sizes and also causes a moderate performance overhead. However, hybrid approaches offer a practical way to switch over. Lattice-based algorithms are particularly advantageous because they provide a strong balance of security, speed, and compatibility with existing systems. Using this information, a method was developed to help organizations gradually transition to a more secure system for managing their digital keys. This thesis connects advanced cryptography research with how businesses actually use it. It offers useful ideas and advice for companies getting ready for an age after quantum computing.