5d3b2cf95d
A browser gives crypto.subtle only to a secure page (https, or http://localhost). Opened any other way, for example a dev server reached over plain http by its LAN address from a phone, every pinned file was refused with a bare "reading 'digest'": the packet printed in English and page 1 fell back to its stored sheet. sha384() now refuses with a sentence that names the cause. check:pinned-fetch-fresh arm D2 removes crypto.subtle and requires that sentence; its self-test plants the unguarded call.
37 lines
2.3 KiB
JavaScript
37 lines
2.3 KiB
JavaScript
// The Subresource-Integrity form of a text's SHA-384 ("sha384-<base64>"), via WebCrypto, so a file fetched at
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// print time can be compared with the pin baked into the bundle (poster-render.integrity.js) before it is used.
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// The same value pin-poster-render.mjs computes with node:crypto.
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// ★ ONLY ON A SECURE PAGE. A browser gives crypto.subtle only to a secure page (https, or http://localhost). Opened any
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// other way (a dev server reached over plain http by its LAN address, from a phone on the same Wi-Fi), every pinned
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// file was refused with a bare "reading 'digest'": the packet printed in English and page 1 fell back to its stored
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// sheet, with nothing saying why. Say it in words.
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export async function sha384(text) {
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const subtle = globalThis.crypto && globalThis.crypto.subtle
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if (!subtle) throw new Error('pinned files can only be checked on a secure page (https, or http://localhost); this page is not one')
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const d = new Uint8Array(await subtle.digest('SHA-384', new TextEncoder().encode(text)))
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let bin = ''
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for (const b of d) bin += String.fromCharCode(b)
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return `sha384-${btoa(bin)}`
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}
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// ★ A PINNED FILE THAT FAILS ITS PIN IS FETCHED ONCE MORE, FRESH. The loaders fetch with cache: 'force-cache' (fast,
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// and it works offline once cached), which returns ANY cached copy, however old. After a re-pin, a reader who had
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// printed before kept the previous file: it failed its pin on every print, and the print fell back without a word
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// (the stored poster for page 1, English for the packet text) until the browser evicted it. So a copy that is not
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// served or does not match is fetched ONCE more with cache: 'reload', which skips the HTTP cache and refreshes it,
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// and only that answer decides. Resolves with the verified text; rejects with the last reason (err.integrity is
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// true when the bytes were wrong rather than missing).
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export async function fetchPinned(url, pin) {
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let last = null
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for (const cache of ['force-cache', 'reload']) {
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try {
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const res = await fetch(url, { cache })
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if (!res.ok) { last = new Error(`not served (${res.status})`); continue }
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const text = await res.text()
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const got = await sha384(text)
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if (got === pin) return text
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last = Object.assign(new Error(`failed its integrity check (expected ${pin}, got ${got})`), { integrity: true })
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} catch (e) { last = e }
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}
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throw last
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}
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