Abstract
We propose and experimentally demonstrate high-speed operation of random-channel cryptography (RCC) in multimode fibers. RCC is a key generation and distribution method based on the random channel state of a multimode fiber and multi-dimension to single-dimension projection. The reciprocal intensity transmittance of the channel shared between the two legitimate users is used to generate and distribute correlated keys. In previous work, RCC's key rate-distance product was limited by the speed of light. In this work, we show that adding a fast modulator at one end of the channel decouples the key rate and distance, resulting in a significant improvement in the key rate-distance product, limited only by the fiber's modal dispersion. Error-free transmission at a key rate-distance product of 64.7 Mbps <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times $</tex-math></inline-formula> 12 km, which is seven orders of magnitude higher than the previous demonstration, was achieved. The proposed method's security arises from a fundamental asymmetry between the eavesdroppers’ and legitimate users’ measurement complexity.
Highlights
Many public-key cryptography methods, which are widely used for encryption over the internet, offer computational security [1,2,3]
In the forward direction, Alice sends onedimensional light which is projected onto the M DOFs of the multimode fiber (MMF)
For our proof-of-concept high-speed random-channel cryptography (RCC) experiment, a laser operating at λ=1550 nm with a linewidth of 100 kHz was split into two by a polarizing beamsplitter (PBS) and injected into both ends of the link
Summary
Many public-key cryptography methods, which are widely used for encryption over the internet, offer computational security [1,2,3]. Since the phase is accumulated over the entire interferometer, recovering the signal is significantly more challenging for an eavesdropper than for the legitimate users This method relies on slow-varying external fluctuations to produce the key, which has limited key rates to 100s bps, many orders of magnitude below communication system bit rates [23,24,25,26,27]. Error-free transmission at a key rate of 64.7 Mbps over 12 km of commercial OM4 fiber was demonstrated using only commercial off-the-shelf components This represents a seven orders of magnitude increase in the key rate-distance product compared to the previous result of 20 bps·km [28]
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