Despite the unconditionally secure theory of the Quantum Key Distribution ($QKD$), several attacks have been successfully implemented against commercial $QKD$ systems. Those systems have exhibited some flaws, as the secret key rate of corresponding protocols remains unaltered, while the eavesdropper obtains the entire secret key. We propose the negative acknowledgment state quantum key distribution protocol as a novel protocol capable of detecting the eavesdropping activity of the Intercept Resend with Faked Sates ($IRFS$) attack without requiring additional optical components different from the $BB84$ protocol because the system can be implemented as a high software module. In this approach, the transmitter interleaves pairs of quantum states, referred to here as parallel and orthogonal states, while the receiver uses active basis selection.

We present a new post-processing method for Quantum Key Distribution (QKD) that raises cubically the secret key rate in the number of double matching detection events. In Shannon’s communication model, information is prepared at Alice’s side, and it is then intended to pass it over a noisy channel. In our approach, secret bits do not rely in Alice’s transmitted quantum bits but in Bob’s basis measurement choices. Therefore, measured bits are publicly revealed, while bases selections remain secret. Our method implements sifting, reconciliation, and amplification in a unique process, and it just requires a round iteration; no redundancy bits are sent, and there is no limit in the correctable error percentage. Moreover, this method can be implemented as a post-processing software into QKD technologies already in use.

We introduce a new integral method for Quantum Key Distribution to perform sifting, reconciliation and amplification processes to establish a cryptographic key through the use of binary matrices called frames which are capable to increase quadratically the secret key rate. Since the eavesdropper has no control on Bob’s double matching detection events, our protocol is not vulnerable to the Intercept and Resend (IR) attack nor the Photon Number Splitting (PNS) attack. The method can be implemented with the usual optical Bennett–Brassard ( $BB84$ ) equipment allowing strong pulses in the quantum regime.

In this work we introduce a new approach for digital signature based on hash chains. The method is supported on the well known security principles of hash functions. Some main advantages of this public key system include security and estimated efficiency through the so called signature chains. In addition, the algorithm is a promissory alternative for digital signatures for the quantum era.

Quantum key distribution (QKD) is a cornerstone of secure communication in the quantum era, yet most existing protocols are designed for point-to-point transmission, limiting their scalability in networked environments. In this work, we introduce Loop-Back QKD, a novel QKD protocol that supports both two-party linear configurations and scalable multiuser ring topologies. By leveraging a structured turn-based mechanism and bidirectional pulse propagation, the protocol enables efficient key distribution while reducing the quantum bit error rate (QBER) through a multi-pulse approach. Unlike trusted-node QKD networks, Loop-Back QKD eliminates intermediate-node vulnerabilities, as secret keys are never processed by intermediate nodes. Furthermore, unlike Measurement-Device-Independent (MDI-QKD) and Twin-Field QKD (TF-QKD), which require complex entanglement-based setups, Loop-Back QKD relies solely on direct polarization transformations, reducing vulnerability to side-channel attacks and practical implementation challenges. Additionally, our analysis indicates that multi-pulse Loop-Back QKD can tolerate higher QBER thresholds. However, this increased robustness comes at the cost of a lower key rate efficiency compared to standard QKD schemes. This design choice enhances its robustness against real-world adversarial threats, making it a strong candidate for secure multiuser communication in local and metropolitan-scale quantum networks.

We investigate a cryptosystem through what we call non-invertible cryptography. As a result of a continuous refinement process, we present a new key exchange method to establish a secret key between two remote parties. Non-invertible KEP is supported by Euler’s theorem as RSA, it uses exponentiation to exchange a secret key as Diffie–Hellman, and it encrypts/decrypts through invertible multiplication as ElGamal. This method is public key; it allows secret key exchange and performs secret communication. Most remarkably, since it does not rely on computational problems as integer factorization or discrete logarithm whose difficulty is conjectured, non-invertible KEP becomes a promising candidate to protect communication in the quantum era. By contrast, the algorithm is supported on indistinguishability of public key and ciphertext so it achieves perfect secrecy. The protocol demonstrates minimum required time for encryption/decryption processes when is compared with the main public key algorithms as Diffie–Hellman, ElGamal or RSA.