NymDrop, anonymous submission over the Nym mixnet (live on my blog)

[Victor]

Hi everybody,

wanted to share something I’ve been building on top of Nym.

A bit of background first:

I run a small blog called Nonlocality - The Observer Effect (archives.virebent.art), independent, self-hosted, no ads, no tracking, no CDN, no analytics, no logs.

The editorial mission is specific: collecting testimonies, analyses, and voices from parts of the world where press freedom and free speech are suppressed, censored, or simply absent, independent journalists working under censorship, researchers whose findings make powerful people uncomfortable, activists documenting abuses.

For that kind of contributor, anonymity isn’t a nice-to-have, it’s the difference between publishing and not being able to say anything at all.

That’s the actual reason I built NymDrop: an anonymous submission tool with the Nym mixnet as its only transport.

Some details on how it works:

• Client-side encryption: everything is encrypted in the browser with X25519 + HKDF-SHA-256 + AES-GCM-256 via WebCrypto before it leaves the source’s machine. The server never sees plaintext.
• No-log, blind relay: the public-facing server writes nothing to disk, no IPs, no timesorwards ciphertext into the mixnet and forgets it.
• Separate reader, offline from the public server: decryption happens on a completely different machine, with an X25519 private key that never touches the internet-facing box. Even if the public server got seized, there’s nothing readable on it.
• Self-contained proof-of-work anti-spam: the browser has to find a hashcash-style nonce before a submission is accepted, no external challenge server, no CAPTCHA, no third-party JS.
• No CDN, no tracking, no NIST curves, only a small Go binary and some vanilla JS, nothing else.

Live instance bolted onto the blog as the actual submission form: https://submit.archives.virebent.art

If you want to look at it or tear it apart:

nymdrop - Nym-native anonymous submission system (SecureDrop-style), using...

Still rough in places, but it’s tested end-to-end and works over the mixnet.

Mostly wanted to show a concrete use case where mixnet transport actually solves a real problem for real people, not just a tech demo.

Happy to hear thoughts, criticism, or better ideas on the design.

Gab

[Ch1ffr3punk]

Hi Gabx,

Nice, however the text is not white and therefore very hard to read on the black background.

Best regards
Ch1ffr3punk

[Victor]

Hi @Ch1ffr3punk

Yes you’re right, now there’s the day/night button

Best regards

Gab

[Ch1ffr3punk]

Ah, ok. Thanks! But it would be IMHO still nice if in dark mode the grey text would be much brighter like white.

Best regards
Ch1ffr3punk

[Victor]

Thanks for the suggestions color choice, it actually looks better

Larger fonts?

[sudonym]

hey, thanks for sharing - this is very cool!

I am getting this error when trying to send a 1.5MB file. Is that beyond the limit?

[Victor]

Hi @sudonym, thanks for the report.

The code tried to convert your whole file into text in one single giant step, and the browser choked on anything bigger than about 1MB.

Fixed that so it processes the file in small pieces instead.

Tested with real files up to ~8.7MB over the mixnet, works fine, just takes a couple minutes to arrive.

That’s normal: Nym deliberately sends traffic slowly and steadily to protect anonymity, it’s not a glitch.

Try again whenever, should go through now.

Best regards

Gab

[Ch1ffr3punk]

I am updating my NymTransfer program for the official nym-client and was nasty and tested large files, but when doing so the exit gateway??? on the receiving site gets sometimes “confused”. So very important is to find the right balance with chunking and rate limiting, which I now implemented in NymTransfer CLI. Not sure if I should make it publicity available, once people would figure out to use it without NymVPN, free of charge, for torrenting…

[Ch1ffr3punk]

$ ./NymTransfer-linux-amd64 -h

A file transfer tool for the Nym Mixnet and official nym-client

USAGE:
Send a file:
nymtransfer -t
nymtransfer -to
nymtransfer -a
nymtransfer -alias

Receive files:
nymtransfer -r
nymtransfer -receive

OPTIONS:
-R float
Chunks per second (default: 1) (default 1)
-a string
Alias name (e.g., bob)
-alias string
Alias name (e.g., bob)
-c int
Chunk size in KiB (default: 64) (default 64)
-chunk-size int
Chunk size in KiB (default: 64) (default 64)
-o string
Output directory for received files (default “./received”)
-out string
Output directory for received files (default “./received”)
-p string
Nym client WebSocket port (default: 1977) (default “1977”)
-port string
Nym client WebSocket port (default: 1977) (default “1977”)
-r Receive mode (listen for files)
-rate float
Chunks per second (default: 1) (default 1)
-receive
Receive mode (listen for files)
-t string
Transfer file to address
-to string
Transfer file to address
-v Show version information
-version
Show version information

ALIAS FILE:
Create NymTransfer.json in the current directory:
{
“aliases”: {
“bob”: “BobNymAddressHere”,
“alice”: “AliceNymAddressHere”
}
}

[Victor]

That’s a useful data point, thanks for sharing.

We hit the same territory today testing NymDrop: max 255 Sphinx fragments per set, client paces real packets at ~50/s by default. Pushed it to 8.7MB using just the stock nym-client fragmentation (no manual chunking on our end) and it arrived clean every time, few minutes delivery. Never saw gateway confusion at that size.

Curious where your threshold was, what file size started causing it, and are you seeing it as a gateway-side rate limit, or more a reassembly/state issue on their end?

Your 64KiB/1 chunk per sec defaults are way more conservative than the client’s native pacing, so if you’re hitting problems even with that, good to know before we ever think about raising our own cap past 10MB.

Regards

Gab Virebent

[Ch1ffr3punk]

Hi Gabx,

NymTransfer itself works as it is a port of OnionTransfer. 100MB, for example is no problem, but I tried also with 1GB and around 300MB I got on the receiving side red errors from nym-client which where caused by the Nym gateway???. I will test this further. On the other side, the Nym Mixnet should be only used for small payloads, like in your case or for email/Usenet etc.

[Ch1ffr3punk]

I just did a test again with 100MB with my very slow Internet connection, which I won’t upgrade in the near future.

The result is IMHO pretty good for the Nym Mixnet, with the official nym-client.

I leave NymTransfer as it is and later if journalists or whistle blowers need to transmit larger files they should split files by themselves and use a break of a couple of minutes between each session, to give the receiving side proper time between each sesssion, due to latency which means that the finishing process on the receiving side takes longer until it reaches 100%.

I attach the .go source code PGP symmetric encrypted and you and the Nym team can DM me here for the password.

Best regards
Ch1ffr3punk

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[Victor]

That answers it then, sounds like it’s gateway-side rather than a client pacing issue, since your defaults are already more conservative than the native fragmentation and you’re still seeing it around 300MB.

Manual split with a break between chunks makes sense as the practical fix for now, better than chasing a gateway bug you can’t control from the client. Good to have that confirmed before anyone assumes 1GB is fine just because 100MB works.

I’ll take you up on the source password, thanks.

Regards

Gab

[Ch1ffr3punk]

Let’s see what the Nym team says, once they are testing. I could enhance NymTransfer with automatic splitting very large files, prior sending and automatic joining on the receiving side, but for now I leave it as it is, because such enhancements would probably invite people for torrenting over the Nym Mixnet, which I do not support, when reading sometimes such things from NymVPN users.

[Victor]

Makes sense to hold off given the torrenting risk. On my side, still curious if anyone here wants to give NymDrop a spin and report back.

NymDrop — Secure Submission

[Ch1ffr3punk]

I will test NymDrop later today. I tried also in the past Wormhole-Nym (Web version) from Alexis, but It is a bit confusing to use and I archived no result.

[Ch1ffr3punk]

Hi Gabx,

I tried NymDrop with exactly 10MB but it gives an error.

$ openssl rand 10485760 > ch1ffr3punk_random_binary_data

$ shasum -a 256 ch1ffr3punk_random_binary_data
f0906bd53981c35e3c233287ad92e35c4b4bd60dbfe7aab1d1ae6c4f00e4c770 ch1ffr3punk_random_binary_data

[Victor]

Found it, thanks for the exact repro.

Turns out there are two base64 layers stacked between the raw file and the mixnet, not one: the browser base64s the file before encrypting it, then our server does a second base64 to hand the ciphertext to the local nym-client over its own WebSocket control API.

The two combine to about 1.78x, and the real wall we hit was nym-client’s own hardcoded 16MB WebSocket message limit, not anything in our code.

A 10MB file was pushing an 18.6MB internal message past that limit.

Fixed by lowering our cap with real margin under that 16MB ceiling.

Honest update: the real safe raw file size is about 8MB, not 10MB like we said before.

Tested it live with your exact scenario, a 10MB file now fails clean and fast instead of the silent “Delivery failed” you saw.

Thanks again for catching this, wouldn’t have found the second base64 layer without a real test at that exact size.

Best regards

Gab

[Ch1ffr3punk]

You’re welcome!

[Ch1ffr3punk]

Hi Gabx,

I have added -split and -pause when a file is larger than 100MB. I send you a DM via TG.