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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
- */