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Geraldo A. Barbosa

Publications and source records attributed to Geraldo A. Barbosa.

16 recordsLinked to original sources
arXiv2025

Polar Coding and Linear Decoding

Polar encoding, described by Arikan in IEEE Transactions on Information Theory, Vol. 55, No. 7, July 2009, was a milestone for telecommunications. A Polar code distributes information among high and low-capacity channels, showing the possibility of achieving perfect channel capacity. The high-capacity channels allow almost noiseless transmission of data. When these channels are not high noise, reliability is achieved in the signal transmission. It starts to compete against codes such a Low-Density Parity-Check (LDPC) codes. Polar code can be also considered error correcting, based on the redundancy inherent in its structure. This feature makes polar encoding also applicable to digital quantum-resistant cryptography protocols. This work explores linear decoding at a first or single trial in the case of small losses or small number of bit-flipping, and repeated transmission for medium level losses. This is distinct from Arikans successive probabilistic decoding by application of probabilistic rules. Linear decoding is done directly from solving the linear equations connecting the codewords x and the received signals y after transmission via noisy channels. Numerical examples will be shown. Along with this work, programming in Mathematica language was used. Codes are available for copy-and-paste for Mathematica users to immediately try the described formalism.

cs.IT↗
arXiv2025

Reply to Structural Vulnerability in Y00 Protocols

The paper arXiv:2412.07300v1 [quant-ph] 10 Dec 2024, entitled "Structural Vulnerability in Y00 Protocols", by Kentaro Imafuku analyzes "Secure Communication Using Mesoscopic Coherent States", Phys. Rev. Lett., 90:227901, Jun 2003, by Geraldo A. Barbosa, Eric Corndorf, Prem Kumar, and Horace P. Yuen. Imafuku states that in his analyzes a structural vulnerability was revealed that enables the leakage of secret information from the measurement results in the Y00 protocol. Furthermore, it is also stated that an even simpler model, but based on the same original principles, can be more efficient than the original Y00 protocol. This reply shows that: 1) the alleged vulnerability is due to a misinterpretation of one result by Imafuku and 2) that the simple model proposed by him is more vulnerable than the original Y00.

quant-ph↗
arXiv2016

A wireless physically secure key distribution system

A secure key distribution protocol protected by light's noise was introduced in 2003 [Phys. Rev. A 68, 052307 (2003)]. That protocol utilized the shot noise of light present in the optical channel (eg., an optical fiber) to restrict information leaks to an adversary. An initial shared information between the legitimate users allowed them to extract more information from the channel than the one obtained by the adversary. That original paper recognized the need for a privacy amplification step but no specific protocol was presented. More recently that original idea was improved with a specific privacy amplification protocol [arXiv:1406.1543v2 [cs.CR] 8 Jul 2015] while keeping the use of an optical communication channel. This work merges main ideas of the protection given by the light's noise in a protocol applied to wireless channels. The use of a wireless channels together with recorded physical noise was introduced from 2005 to 2007 (see eg, arXiv:quant-ph/0510011 v2 16 Nov 2005 and arXiv:0705.2243v2 [quant-ph] 17 May 2007). This work improves those embrionary ideas of wireless channels secured by recorded optical noise. The need for specific optical channels is eliminated with the wireless variation and opens up the possibility to apply the technique to mobile devices. This work introduces this new scheme and calculates the associated security level.

cs.CR↗
arXiv2015

Untappable key distribution system: a one-time-pad booster

One-time-pad (OTP) encryption simply cannot be cracked, even by a quantum computer. The need of sharing in a secure way supplies of symmetric random keys turned the method almost obsolete as a standing-alone method for fast and large volume telecommunication. Basically, this secure sharing of keys and their renewal, once exhausted, had to be done through couriers, in a slow and costly process. This paper presents a solution for this problem providing a fast and unlimited renewal of secure keys: An untappable key distribution system is presented and detailed. This fast key distribution system utilizes two layers of confidentially protection: 1) Physical noise intrinsic to the optical channel that turn the coded signals into stealth signals and 2) Privacy amplification using a bit pool of refreshed entropy run after run, to eliminate any residual information. The resulting level of security is rigorously calculated and demonstrates that the level of information an eavesdropper could obtain is completely negligible. The random bit sequences, fast and securely distributed, can be used to encrypt text, data or voice.

cs.CR↗
arXiv2012

Can humans see beyond intensity images?

The human's visual system detect intensity images. Quite interesting, detector systems have shown the existence of different kind of images. Among them, images obtained by two detectors (detector array or spatially scanning detector) capturing signals within short window times may reveal a "hidden" image not contained in either isolated detector: Information on this image depend on the two detectors simultaneously. In general, they are called "high-order" images because they may depend on more than two electric fields. Intensity images depend on the square of magnitude of the light's electric field. Can the human visual sensory system perceive high-order images as well? This paper proposes a way to test this idea. A positive answer could give new insights on the "visual-conscience" machinery, opening a new sensory channel for humans. Applications could be devised, e.g., head position sensing, privacy in communications at visual ranges and many others.

q-bio.NC↗
arXiv2007

Transverse coincidence-structures in spontaneous parametric down-conversion with orbital angular momentum: Theory

Coincidence-structures in the transverse plane of Type-II spontaneous parametric down-conversion carrying orbital angular momentum are obtained. Azimuthal symmetry breaking around the pump beam direction reveals itself on these quantum images. Analytical expressions for the amplitude probability of the down conversion process are shown including the nonlinear polarizability components.

quant-ph↗
arXiv2007

Secure sharing of random bits over the Internet

Although one-time pad encrypted files can be sent through Internet channels, the need for renewing shared secret keys have made this method unpractical. This work presents a scheme to turn practical the fast sharing of random keys over arbitrary Internet channels. Starting with a shared secret key sequence of length K_0 the users end up with a secure new sequence K >> K_0. Using these sequences for posteriori message encryption the legitimate users have absolute security control without the need for third parties. Additionally, the security level does not depend on the unproven difficulty of factoring numbers in primes. In the proposed scheme a fast optical random source generates random bits and noise for key renewals. The transmitted signals are recorded signals that carries both the random binary signals to be exchanged and physical noise that cannot be eliminated by the attacker. These signals allow amplification over the Internet network without degrading security. The proposed system is also secure against a-posteriori known-plaintext attack on the key. Information-theoretic analysis is presented and bounds for secure operation are quantitatively determined.

quant-ph↗
arXiv2007

Is orbital angular momentum always conserved in spontaneous parametric down-conversion?

In the non-linear optical process of type-II spontaneous parametric down-conversion, we present on an experiment showing that the two-photon detection amplitude of the down-converted beams does not generally reproduce the transverse profile of the pump beam that carries non-zero orbital angular momentum. We explain this observation by that orbital angular momentum is not conserved in the type-II non-linear process due to the broken rotational symmetry of the Hamiltonian.

quant-ph↗
arXiv2007

One-time pad booster for Internet

One-time pad encrypted files can be sent through Internet channels using current Internet protocols. However, the need for renewing shared secret keys make this method unpractical. This work shows how users can use a fast physical random generator based on fluctuations of a light field and the Internet channel to directly boost key renewals. The transmitted signals are deterministic but carries imprinted noise that cannot be eliminated by the attacker. Thus, a one-time pad for Internet can be made practical. Security is achieved without third parties and not relying on the difficulty of factoring numbers in primes. An informational fragility to be avoided is discussed. Information-theoretic analysis is presented and bounds for secure operation are determined.

quant-ph↗
arXiv2007

The conservation of orbital angular momentum and the two-photon detection amplitude in spontaneous parametric down-conversion

We study the two-photon detection amplitude of the down-converted beams in spontaneous parametric down-conversion when the physical variable of orbital angular momentum is involved, taking into account both conservation and non-conservation of angular momentum. Agreeing with experimental observations, our theoretical calculation shows that spatial structure of the two-photon detection amplitude of the down-converted beams carries important information about conservation or non-conservation of orbital angular momentum in spontaneous parametric down-conversion.

quant-ph↗
arXiv2006

Fundamentals for immediate implementation of a quantum secured Internet

This work shows how a secure Internet for users A and B can be implemented through a fast key distribution system that uses physical noise to encrypt information transmitted in deterministic form. Starting from a shared secret random sequence between them, long sequences of fresh random bits can be shared in a secure way and not involving a third party. The shared decrypted random bits -encrypted by noise at the source- are subsequently utilized for one-time-pad data encryption. The physical generated protection is not susceptible to advances in computation or mathematics. In particular, it does not depend on the difficulty of factoring numbers in primes. Also, there is no use of Linear Feed Back Shift Registers. The attacker has free access to the communication channels and may acquire arbitrary number of copies of the transmitted signal without lowering the security level. No intrusion detection method is needed.

quant-ph↗
arXiv2006

Noise Secured Internet

This work shows how a secure Internet can be implemented through a fast key distribution system that uses physical noise to protect the transmitted information. Starting from a shared random sequence $K_0$ between two (or more) users, longsequences $R$ of random bits can be shared. The signals sent over the Internet are deterministic but have a built-in Nature-made uncertainty that protects the shared sequences. After privacy amplification the shared $R$ random bits --encrypted by noise-- are subsequently utilized in one-time-pad data ciphering.

quant-ph↗
arXiv2004

Fast and secure key distribution using mesoscopic coherent states of light

This work shows how two parties A and B can securely share sequences of random bits at optical speeds. A and B possess true-random physical sources and exchange random bits by using a random sequence received to cipher the following one to be sent. A starting shared secret key is used and the method can be described as an unlimited one-time-pad extender. It is demonstrated that the minimum probability of error in signal determination by the eavesdropper can be set arbitrarily close to the pure guessing level. Being based on the $M$-ry encryption protocol this method also allows for optical amplification without security degradation, offering practical advantages over the BB84 protocol for key distribution.

quant-ph↗
arXiv2003

Secure communication using coherent states

We demonstrate that secure communication using coherent states is possible. The optimal eavesdropping strategy for an M-ry ciphering scheme shows that the minimum probability of error in a measurement for bit determination can be made arbitrarily close to the pure guessing value P_e=1/2. This ciphering scheme can be optically amplified without degrading the security level. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels.

quant-ph↗
arXiv2003

Secure communication using mesoscopic coherent states

We demonstrate theoretically and experimentally that secure communication using intermediate-energy (mesoscopic) coherent states is possible. Our scheme is different from previous quantum cryptographic schemes in that a short secret key is explicitly used and in which quantum noise hides both the bit and the key. This encryption scheme can be optically amplified. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels.

quant-ph↗