# ASiC-E Online Viewer: how it works inside your browser

> An ASiC-E online viewer sounds like a website that processes your file. In reality the website only delivers the program. The work happens in your browser.

Source: https://asiceviewer.com/en/blog/asice-online-viewer/
Published: 2026-11-10 · Digixy

## In short

- The viewer is a JavaScript application executed by your own browser.
- It reads the ZIP structure, parses the signature XML and recomputes digests with the Web Crypto API.
- No server component ever receives the document.

## Step 1: reading the file

When you drop a file onto [the viewer](https://asiceviewer.com/en/#tool), the browser hands the page a reference to it. The page reads the bytes into memory with the standard File API. Nothing is transmitted; the bytes move from your disk to a browser tab.

## Step 2: unpacking the ZIP

An `.asice` container is a ZIP archive. The viewer reads the archive's directory, finds `mimetype` and the entries under `META-INF`, and decompresses individual files only when they are needed. A large PDF is not unpacked until you click it.

## Step 3: reading the signatures

Each `signatures*.xml` file is parsed with the browser's built-in XML parser. From it the viewer extracts:

- the signer's certificate, decoded from its ASN.1 structure to get the name, personal code, issuer and validity period;
- the signing time and, if present, the time stamp;
- the role and place the signer entered;
- the list of signed files with a digest for each.

## Step 4: checking integrity

For every signed file the viewer computes a fresh digest (usually SHA-256) through the Web Crypto API and compares it with the value in the signature. A match means the file is exactly what was signed. A mismatch produces a red warning that names the file.

## Step 5: rendering the document

| Document type | How it is displayed |
| PDF | Rendered page by page onto a canvas |
| DOCX | Converted to HTML in the browser |
| XLSX, XLS, ODS, CSV | Shown as a table, one tab per sheet |
| Images, audio, video | Native browser elements |
| Text, XML, JSON | Decoded and formatted |

## What this design means for you

Because there is no server step, there is no queue, no size quota set by a provider and no copy of your contract on someone else's disk. The limit is your device's memory. The trade-off is that an online viewer cannot do what needs a trusted server or a smart card. See [what an online viewer can and cannot do](https://asiceviewer.com/en/blog/online-asice-file-viewer/).

## Frequently asked questions

**Which browsers can run an ASiC-E online viewer?**

Any current version of Chrome, Edge, Firefox, Safari, Opera or Samsung Internet. JavaScript must be enabled.

**Is the viewer's code loaded from third parties?**

No. ASiCE Viewer serves every library from its own domain and sets a content security policy that blocks other sources.

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Open your .asice file now: https://asiceviewer.com/en/
ASiC-E Viewer on Google Play: https://play.google.com/store/apps/details?id=com.digixy.asiceviewer