{
  "abstract": "Recent work in quantum key distribution (QKD) has yielded finite-size keyrates based on convex optimisation problems, using the framework of entropy accumulation. Multiple solvers have been developed to address these optimisations in recent years, but have been based on a somewhat elaborate framework using sophisticated algorithms, in order to accommodate a broad range of QKD protocols. In this work, we note that for basic QKD protocols such as qubit BB84, the keyrates can be easily computed using off-the-shelf solvers instead, by obtaining suitable tangent lines to lower bound terms in the objective function. We compute the resulting finite-size keyrates and compare them to previous work. Moreover, we extend this approach to the six-state protocol, by deriving closed-form expressions for the single-round Rényi entropies in the protocol. This should facilitate subsequent study of the six-state protocol via entropy accumulation.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.09847",
  "author_total": 2,
  "authors": [
    {
      "name": "Jun Hui Goh"
    },
    {
      "name": "Ernest Y. -Z. Tan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/aw186nffp1c14.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.09847",
  "fulltext_url": null,
  "id": "aw186nffp1c14",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.09847",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "quant-ph"
    ],
    [
      "openalex",
      "1702|Quantum Information and Cryptography"
    ]
  ],
  "openalex": "W7212141917",
  "pdf_url": "https://arxiv.org/pdf/2609.09847",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-09",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/aw186nffp1c14.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:12Z",
      "native_id": "2609.09847",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.09847"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:quant-ph",
      "subfield": "quantum"
    }
  ],
  "title": "Simple QKD keyrate computations from tangent-line bounds",
  "title_text": "Simple QKD keyrate computations from tangent-line bounds",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:12Z",
  "url": "https://research.draconitic.com/paper/aw186nffp1c14",
  "venue": "arXiv",
  "versions": []
}