The Tool Desk
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You can calculate an APK’s SHA-256 checksum in a browser without uploading the file: let the user choose the APK, read its bytes with File.arrayBuffer(), and pass the resulting buffer to crypto.subtle.digest("SHA-256", buffer). The result is a fingerprint of those exact file bytes—not a malware scan or a check of the APK’s Android signing certificate.
Build the local APK checksum page
Save this as an HTML file and serve it from a secure context, such as an HTTPS site or localhost. The file extension is only a selection hint; choosing a file ending in .apk does not establish that its contents are a valid APK.
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<!doctype html>
<html lang="en">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Local APK SHA-256 checker</title>
<h1>Local APK SHA-256 checker</h1>
<p>This page hashes the selected file in your browser. It does not upload the file, scan for malware, or verify an APK signature.</p>
<label for="apk">Choose APK</label>
<input id="apk" type="file" accept=".apk,application/vnd.android.package-archive">
<label for="expected">Expected SHA-256 (optional)</label>
<input id="expected" type="text" spellcheck="false" autocomplete="off">
<button id="copy" type="button" disabled>Copy SHA-256</button>
<p id="status" role="status" aria-live="polite">Choose a file to calculate its SHA-256 checksum.</p>
<p>File: <span id="filename">None</span></p>
<p>Algorithm: SHA-256</p>
<p>SHA-256: <code id="digest">—</code></p>
<p id="comparison"></p>
<script>
const apkInput = document.querySelector("#apk");
const expectedInput = document.querySelector("#expected");
const status = document.querySelector("#status");
const filename = document.querySelector("#filename");
const digestOutput = document.querySelector("#digest");
const comparison = document.querySelector("#comparison");
const copyButton = document.querySelector("#copy");
let currentDigest = "";
function compareExpected() {
const expected = expectedInput.value.trim();
if (!currentDigest || !expected) {
comparison.textContent = "";
} else if (!/^[0-9a-f]{64}$/i.test(expected)) {
comparison.textContent = "Enter a 64-character hexadecimal SHA-256 value to compare.";
} else {
comparison.textContent = expected.toLowerCase() === currentDigest
? "Match: the selected file has this SHA-256 value."
: "No match: the selected file has a different SHA-256 value.";
}
}
expectedInput.addEventListener("input", compareExpected);
copyButton.addEventListener("click", async () => {
try {
await navigator.clipboard.writeText(currentDigest);
status.textContent = "SHA-256 copied.";
} catch {
status.textContent = "Copy failed. Select and copy the displayed SHA-256 value.";
}
});
apkInput.addEventListener("change", async () => {
const file = apkInput.files[0];
currentDigest = "";
digestOutput.textContent = "—";
comparison.textContent = "";
copyButton.disabled = true;
filename.textContent = file ? file.name : "None";
if (!file) {
status.textContent = "Choose a file to calculate its SHA-256 checksum.";
return;
}
if (!globalThis.crypto?.subtle || typeof file.arrayBuffer !== "function") {
status.textContent = "SHA-256 is unavailable here. Use a supported browser in a secure context, such as HTTPS or localhost.";
return;
}
status.textContent = "Reading file and calculating SHA-256…";
try {
const buffer = await file.arrayBuffer();
const hash = await crypto.subtle.digest("SHA-256", buffer);
currentDigest = Array.from(new Uint8Array(hash), byte =>
byte.toString(16).padStart(2, "0")
).join("");
digestOutput.textContent = currentDigest;
copyButton.disabled = false;
status.textContent = "SHA-256 calculated locally in this page.";
compareExpected();
} catch {
status.textContent = "Could not read or hash this file. Try selecting it again.";
}
});
</script>
</html>What the code does
- The file input gives the page a user-selected
File. Its name is displayed, but the extension is not treated as proof of file type. file.arrayBuffer()reads the file bytes, andcrypto.subtle.digest("SHA-256", buffer)calculates the digest. The Web Crypto digest API needs the complete input in memory rather than processing it as a stream, so large files can require substantial memory. MDN documents the full-buffer requirement and secure-context constraint.- The digest is returned as binary data. The code converts each byte to two lowercase hexadecimal characters, preserving leading zeroes, then displays the result and enables copying.
- If an expected checksum is entered, the page trims surrounding whitespace, validates a 64-character hexadecimal value, and compares without regard to letter case.
Understand what a checksum match proves
A SHA-256 comparison answers whether the selected file’s bytes produce the same digest as the expected value. It does not identify who created the APK, establish that the file is safe, or validate Android’s APK-signing scheme. The comparison is useful only when the expected checksum comes from a source you trust; a checksum taken from the same untrusted download channel does not establish the file’s origin. MDN’s file-checksum example uses the same general read-bytes, digest, and convert-to-hex workflow.
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Use Android’s tool to verify an APK signature
If the question is whether an APK’s Android signature verifies, use Android SDK Build Tools’ apksigner, not a browser checksum page. With the APK available as app.apk, run:
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| Workflow | What it checks | What you need | Evidence it produces |
|---|---|---|---|
| Browser SHA-256 comparison | Whether the exact selected file bytes match a known digest | A browser supporting Web Crypto and a checksum obtained through a trusted channel | A hexadecimal digest and, if supplied, a match or mismatch |
apksigner verify |
Whether the APK’s Android signature verifies | Android SDK Build Tools with apksigner and the APK file |
Signature verification result; --print-certs also displays certificate data |
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