demo · v141

Script Integrity Checker

Paste a <script> tag, parse the integrity attribute, and understand what algorithm you're using. Generate a real SHA-384 hash via the Web Crypto API, and explore how Ed25519 signature-based integrity differs from static hash-based SRI.

probing SubtleCrypto and signature-based integrity support…

Parse an integrity attribute

Paste a <script> tag and press "Parse & analyse".

Generate SHA-384 hash

Paste script source text to compute the base64-encoded SHA-384 digest — the value you'd put after sha384- in an integrity attribute.

Enter script content and press "Compute SHA-384".

Signature-based integrity: how it works

With Ed25519, the CDN signs each response. The browser verifies using the public key embedded in the integrity attribute. Any content signed by that private key passes — no hash update needed for new builds.

<!-- Ed25519 signature-based integrity -->
<script src="https://cdn.example/app.js"
        integrity="ed25519-[base64url-encoded-public-key]"
        crossorigin="anonymous"></script>

<!-- Server adds header on each response: -->
Signature: sig=:base64encodedSig:;keyid="app-key-v1";tag="sri"

<!-- Browser verifies: signature over response body matches public key.
     ANY content signed by the private key passes — including new builds. -->

Press "Simulate verification" to generate a real Ed25519 key pair and sign + verify a payload.

Hash-based vs signature-based: the trade-off

sha384

Hash-based SRI

Integrity value is a digest of exact content
Any content change → different hash → browser blocks
You must update every <script> tag on new builds
Works offline — no server-side signing required
Protects against CDN serving wrong version
Does not protect against origin compromise (attacker resigns)

ed25519

Signature-based SRI

Integrity value is the publisher's public key
Any content signed by the private key passes
No HTML changes needed on new builds — only re-sign
Requires CDN/server-side signing infrastructure
Key rotation: update public key in HTML once, rotate private key on server
Protects supply chain: CDN can't forge signatures without the private key

Scenario matrix

Scenario	Hash SRI outcome	Signature SRI outcome
Legitimate new build, same HTML	BLOCK — hash mismatch	PASS — signed by same key
CDN serves stale cached file	BLOCK — hash mismatch	BLOCK — old signature invalid for new response
Transit tampering (MITM)	BLOCK — hash mismatch	BLOCK — forged signature won't verify
CDN account compromised, attacker injects script	PASS (if attacker serves original file)	BLOCK — attacker cannot sign without private key
Private key rotated, HTML not yet updated	PASS (hash still matches)	BLOCK — old public key won't verify new signatures