{"id":224779,"date":"2026-09-07T17:38:14","date_gmt":"2026-09-07T17:38:14","guid":{"rendered":"https:\/\/neodata.com.uy\/labs\/?page_id=224779"},"modified":"2026-09-09T20:11:18","modified_gmt":"2026-09-09T20:11:18","slug":"in-practice","status":"publish","type":"page","link":"https:\/\/neodata.com.uy\/labs\/in-practice\/","title":{"rendered":"In Practice"},"content":{"rendered":"
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\/\/ In Practice<\/p>

Selected work in context.<\/h1>

Applied notes on cryptographic transition, key architecture and constrained systems, with the operational assumptions kept visible.<\/p>

Browse applied work<\/a>About the lab<\/a><\/div><\/div><\/section>\r\n

\/\/ Field implementations<\/p>

Applied work and operational lessons.<\/h2><\/div>

Cryptographic mechanisms considered as parts of live systems rather than isolated primitives.<\/p><\/div>

\r\n \r\n \"Open <\/a>\r\n
\r\n
\r\n Signature Footprint Engineering \u00b7 Part 3<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

The payload must fit the channel.<\/a><\/h3>\r\n

A compact signed object needs one deterministic binary form and three explicit transport profiles. QR, NFC and Bluetooth LE fail in different ways when signature and key material cross their\u2026<\/p>\r\n

\r\n \r\n \"Glass <\/a>\r\n
\r\n
\r\n Signature Footprint Engineering \u00b7 Part 2<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

A selective proof is not automatically smaller.<\/a><\/h3>\r\n

When attributes require independent signatures, BBS can replace N signatures with one multi-message signature, but its selective-disclosure proof grows with every hidden message. The useful crossover depends on what the\u2026<\/p>\r\n

\r\n \r\n \"Close-up <\/a>\r\n
\r\n
\r\n Signature Footprint Engineering \u00b7 Part 1<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

The signature is not the key.<\/a><\/h3>\r\n

A byte-level comparison of RSA, elliptic-curve, pairing-based and post-quantum signatures shows when recurring signature traffic overtakes key provisioning and storage.<\/p>\r\n

\r\n \r\n \"Phone <\/a>\r\n
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\r\n Offline Visual Exchange \u00b7 Part 3<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

A secure key cannot make a photographed QR fresh.<\/a><\/h3>\r\n

Hardware-backed signing can prove which mobile key produced an offline QR. It cannot, by itself, prove that the image was created for this verifier, this place or this moment.<\/p>\r\n

\r\n \r\n \"Smartphone <\/a>\r\n
\r\n
\r\n Offline Visual Exchange \u00b7 Part 2<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

Three hundred milliseconds is an operating envelope.<\/a><\/h3>\r\n

Encrypted QR decoding is governed less by cipher choice than by symbol density, module sampling, optics, motion, exposure and the scanner pipeline. A byte budget and a declared test envelope\u2026<\/p>\r\n

\r\n \r\n \"Two <\/a>\r\n
\r\n
\r\n Offline Visual Exchange \u00b7 Part 1<\/a>\r\n Analysis<\/span>\r\n <\/div>\r\n

A one-way QR can establish a key, but not a conversation.<\/a><\/h3>\r\n

An ephemeral X25519 key can protect an offline QR for a pre-provisioned verifier, but freshness, replay resistance and sender authentication still require explicit protocol state.<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Primer<\/span>\r\n <\/div>\r\n

Putting the trust boundary beside the reader.<\/a><\/h3>\r\n

A SAM can keep master keys out of reader firmware and perform card protocols locally. The security result still depends on permissions, host integration and lifecycle.<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Analysis<\/span>\r\n <\/div>\r\n

A card migration is a state machine.<\/a><\/h3>\r\n

Moving a live fare system from MIFARE Classic to MIFARE Plus is not a card replacement exercise. It is a controlled transition across credentials, readers, keys and operational states.<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n Featured<\/span>\r\n Analysis<\/span>\r\n <\/div>\r\n

Designing a fare token for intermittent connectivity.<\/a><\/h3>\r\n

When balance and fare rules remain in a central account, a QR code is not the ticket. It is a compact claim whose meaning depends on connectivity, trust and replay\u2026<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Primer<\/span>\r\n <\/div>\r\n

The SIM as a cryptographic computer.<\/a><\/h3>\r\n

Long before the secure element became a general platform, SIM and UICC applets provided a small governed environment for keys, authentication and digital signatures.<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Analysis<\/span>\r\n <\/div>\r\n

The token is the easy part.<\/a><\/h3>\r\n

A token can replace a sensitive value. The difficult work is defining what the replacement means, who may reverse it and how the system behaves over time.<\/p>\r\n

\r\n \r\n \"Shattered <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Analysis<\/span>\r\n <\/div>\r\n

Keys without a secure boundary.<\/a><\/h3>\r\n

When cryptographic operations must run without an HSM, software can reduce the exposure of key material\u2014but it cannot make a hostile host trustworthy.<\/p>\r\n

\r\n \r\n \"A <\/a>\r\n
\r\n
\r\n In Practice<\/span>\r\n Primer<\/span>\r\n <\/div>\r\n

When a QR code was not a format.<\/a><\/h3>\r\n

During the pandemic, visually similar QR codes carried incompatible data models, encodings and trust assumptions. A contribution from Uruguay to PathCheck\u2019s Universal Verifier made that fragmentation tangible.<\/p>\r\n