guix - Wojtek's customized Guix

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/** * This file is part of Haketilo. * * Functions: Operations related to "signing" of data. * * Copyright (C) 2021 Wojtek Kosior * Redistribution terms are gathered in the `copyright' file. */ /* * IMPORTS_START * IMPORT sha256 * IMPORT browser * IMPORT is_mozilla * IMPORTS_END */ /* * In order to make certain data synchronously accessible in certain contexts, * Haketilo smuggles it in string form in places like cookies, URLs and headers. * When using the smuggled data, we first need to make sure it isn't spoofed. * For that, we use this pseudo-signing mechanism. * * Despite what name suggests, no assymetric cryptography is involved, as it * would bring no additional benefits and would incur bigger performance * overhead. Instead, we hash the string data together with some secret value * that is supposed to be known only by this browser instance. Resulting hash * sum plays the role of the signature. In the hash we also include current * time. This way, even if signed data leaks (which shouldn't happen in the * first place), an attacker won't be able to re-use it indefinitely. * * The secret shared between execution contexts has to be available * synchronously. Under Mozilla, this is the extension's per-session id. Under * Chromium, this is a dummy web-accessible-resource name that resides in the * manifest and is supposed to be constructed by each user using a unique value * (this is done automatically by `build.sh'). */ function get_secret() { if (is_mozilla) return browser.runtime.getURL("dummy"); return chrome.runtime.getManifest().web_accessible_resources .map(r => /^chromium-key-dummy-file-(.*)/.exec(r)).filter(r => r)[0][1]; } function extract_signed(signature, signed_data) { const match = /^([1-9][0-9]{12}|0)_(.*)$/.exec(signed_data); if (!match) return {fail: "bad format"}; const result = {time: parseInt(match[1]), data: match[2]}; if (sign_data(result.data, result.time)[0] !== signature) result.fail = "bad signature"; return result; } /* * Sign a given string for a given time. Time should be either 0 or in the range * 10^12 <= time < 10^13. */ function sign_data(data, time) { return [sha256(get_secret() + time + data), `${time}_${data}`]; } /* * EXPORTS_START * EXPORT extract_signed * EXPORT sign_data * EXPORTS_END */


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