What Affects Upload & Encryption Speed: File Size, Browser Memory, and Internet Connection
SecureEU Team
Privacy & Security
When you upload a file to SecureEU, your browser does the heavy lifting: it encrypts every byte locally with AES-256-GCM, then uploads the encrypted chunks to our EU servers. The total time this takes depends on three factors: file size, available browser memory, and internet upload speed.
Factor 1: File Size
This one is straightforward — the bigger the file, the longer it takes. Your file is split into 5 MB chunks, and each chunk is independently encrypted and uploaded. A 100 MB file produces about 20 chunks; a 10 GB file produces about 2,048 chunks.
⚡ Chunk-Based Processing
Every file — regardless of size — is processed in 5 MB chunks. Each chunk gets its own AES-256-GCM encryption pass with a unique 12-byte IV and 16-byte authentication tag. This means encryption time scales linearly with file size.
| File Size | Chunks | Encryption Overhead |
|---|---|---|
| 100 MB | ~20 | 560 bytes |
| 1 GB | ~205 | 5,740 bytes |
| 10 GB | ~2,048 | 57,344 bytes |
| 50 GB | ~3,200 | 89,600 bytes |
Encryption overhead is negligible — less than 90 KB even for a 50 GB file.
Factor 2: Browser Memory
Because encryption happens entirely in your browser using the WebCrypto API, your browser needs enough memory to hold at least a few chunks at once. SecureEU processes chunks in a streaming fashion — it doesn't load the entire file into memory — but it does need to buffer the current chunk being encrypted plus any chunks waiting for upload.
With 6× parallel uploads (3 encryption + 3 uploading simultaneously), your browser typically holds 3–6 chunks in memory at once — that's roughly 48–96 MB of RAM. This is well within reach for any modern browser on a desktop or laptop.
On mobile devices or tabs with many other pages open, available memory may be more limited. If your browser is under memory pressure, encryption may slow down as the JavaScript engine pauses for garbage collection. For the best experience with files over 1 GB, we recommend:
- Close unnecessary tabs — each tab consumes memory
- Use a desktop browser — Chrome, Firefox, or Edge on desktop have more memory available than mobile
- Avoid other heavy web apps — video calls, Google Docs, and similar apps compete for resources
Factor 3: Internet Upload Speed
For most users, upload speed is the bottleneck. Home internet connections often have asymmetric speeds — you might have 100 Mbps download but only 10–20 Mbps upload. SecureEU mitigates this with parallel chunk uploading: up to 6 chunks are in flight simultaneously, which maximises your connection utilisation.
📊 Estimated Upload Times
| File Size | 10 Mbps | 50 Mbps | 100 Mbps |
|---|---|---|---|
| 100 MB | ~1.5 min | ~16 sec | ~8 sec |
| 1 GB | ~14 min | ~3 min | ~1.5 min |
| 5 GB | ~70 min | ~14 min | ~7 min |
| 10 GB | ~2.3 hrs | ~27 min | ~14 min |
Times include encryption + parallel upload. Actual speeds depend on network conditions.
How We Optimise the Process
SecureEU uses several techniques to make transfers as fast as possible:
- 5 MB chunk size — small enough for efficient memory use, large enough to minimise HTTP overhead
- Parallel upload pipeline — while one chunk encrypts, previously encrypted chunks are already uploading
- S3-compatible multipart uploads — for large files, each chunk uploads as a separate part, then gets assembled server-side
- Real-time progress — you see exact percentage, speed, and estimated time remaining during the transfer
Two Distinct Phases
When you watch your transfer progress, you'll notice two phases:
- Phase 1 — Encryption: Your browser reads the file, encrypts each 5 MB chunk with AES-256-GCM, and queues them for upload. This phase is limited by your CPU and available memory.
- Phase 2 — Upload: Encrypted chunks are uploaded in parallel to our Hetzner S3 storage in Helsinki, Finland. This phase is limited by your internet upload speed.
In practice, both phases overlap — encryption and uploading happen simultaneously. But if your internet is fast and your device is slow (e.g. an older phone), encryption becomes the bottleneck. If your device is fast but your connection is slow, you'll see chunks encrypt quickly and then wait for uploads to finish.
The Bottom Line
The time to prepare your secure download link is proportional to your file size, constrained by your browser's available memory, and ultimately limited by your internet upload speed. For most users, upload speed is the dominant factor. Encryption itself is fast — modern browsers handle AES-256-GCM at hundreds of megabytes per second via the hardware-accelerated WebCrypto API.
You can check your upload speed at fast.com to estimate how long your transfer will take.