dorsal/arxiv
View SchemaA Practical Trojan Horse for Bell-inequality-based Quantum Cryptography
| Authors | Jan-Åke Larsson |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0111073 |
| URL | https://arxiv.org/abs/quant-ph/0111073 |
| DOI | 10.26421/QIC2.6-2 |
| Journal | Quantum Information and Computation, 2:434 (2002) |
Abstract
Quantum Cryptography, or more accurately, Quantum Key Distribution (QKD) is based on using an unconditionally secure ``quantum channel'' to share a secret key among two users. A manufacturer of QKD devices could, intentionally or not, use a (semi-)classical channel instead of the quantum channel, which would remove the supposedly unconditional security. One example is the BB84 protocol, where the quantum channel can be implemented in polarization of single photons. Here, use of several photons instead of one to encode each bit of the key provides a similar but insecure system. For protocols based on violation of a Bell inequality (e.g., the Ekert protocol) the situation is somewhat different. While the possibility is mentioned by some authors, it is generally thought that an implementation of a (semi-)classical channel will differ significantly from that of a quantum channel. Here, a counterexample will be given using an identical physical setup as is used in photon-polarization Ekert QKD. Since the physical implementation is identical, a manufacturer may include this modification as a Trojan Horse in manufactured systems, to be activated at will by an eavesdropper. Thus, the old truth of cryptography still holds: you have to trust the manufacturer of your cryptographic device. Even when you do violate the Bell inequality.
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"abstract": "Quantum Cryptography, or more accurately, Quantum Key Distribution (QKD) is\nbased on using an unconditionally secure ``quantum channel\u0027\u0027 to share a secret\nkey among two users. A manufacturer of QKD devices could, intentionally or not,\nuse a (semi-)classical channel instead of the quantum channel, which would\nremove the supposedly unconditional security. One example is the BB84 protocol,\nwhere the quantum channel can be implemented in polarization of single photons.\nHere, use of several photons instead of one to encode each bit of the key\nprovides a similar but insecure system. For protocols based on violation of a\nBell inequality (e.g., the Ekert protocol) the situation is somewhat different.\nWhile the possibility is mentioned by some authors, it is generally thought\nthat an implementation of a (semi-)classical channel will differ significantly\nfrom that of a quantum channel. Here, a counterexample will be given using an\nidentical physical setup as is used in photon-polarization Ekert QKD. Since the\nphysical implementation is identical, a manufacturer may include this\nmodification as a Trojan Horse in manufactured systems, to be activated at will\nby an eavesdropper. Thus, the old truth of cryptography still holds: you have\nto trust the manufacturer of your cryptographic device. Even when you do\nviolate the Bell inequality.",
"arxiv_id": "quant-ph/0111073",
"authors": [
"Jan-\u00c5ke Larsson"
],
"categories": [
"quant-ph"
],
"doi": "10.26421/QIC2.6-2",
"journal_ref": "Quantum Information and Computation, 2:434 (2002)",
"title": "A Practical Trojan Horse for Bell-inequality-based Quantum Cryptography",
"url": "https://arxiv.org/abs/quant-ph/0111073"
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