It’s the first idea I had when it came to making sure login on my server is secure. Instead of having a small password that relies on my fallinble memory and may be also guessed in a not-completely-rodiculous amount of time.
Meanwhile a fairly small file, something like a 512 byte “user.key”, to be uploaded along with your username, or even just having your username built-in, seems much safer.
I wanted to do some math but I could only find limited calculators for doing calculations with such big numbers so have the amount of possible combinations the file may have:
256^512
1,044,388,881,413,152,506,691,752,710,716,624,382,579,964,249,047,383,780,384,233,483,283,953,907,971,557,456,848,826,811,934,997,558,340,890,106,714,439,262,837,987,573,438,185,793,607,263,236,087,851,365,277,945,956,976,543,709,998,340,361,590,134,383,718,314,428,070,011,855,946,226,376,318,839,397,712,745,672,334,684,344,586,617,496,807,908,705,803,704,071,284,048,740,118,609,114,467,977,783,598,029,006,686,938,976,881,787,785,946,905,630,190,260,940,599,579,453,432,823,469,303,026,696,443,059,025,015,972,399,867,714,215,541,693,835,559,885,291,486,318,237,914,434,496,734,087,811,872,639,496,475,100,189,041,349,008,417,061,675,093,668,333,850,551,032,972,088,269,550,769,983,616,369,411,933,015,213,796,825,837,188,091,833,656,751,221,318,492,846,368,125,550,225,998,300,412,344,784,862,595,674,492,194,617,023,806,505,913,245,610,825,731,835,380,087,608,622,102,834,270,197,698,202,313,169,017,678,006,675,195,485,079,921,636,419,370,285,375,124,784,014,907,159,135,459,982,790,513,399,611,551,794,271,106,831,134,090,584,272,884,279,791,554,849,782,954,323,534,517,065,223,269,061,394,905,987,693,002,122,963,395,687,782,878,948,440,616,007,412,945,674,919,823,050,571,642,377,154,816,321,380,631,045,902,916,136,926,708,342,856,440,730,447,899,971,901,781,465,763,473,223,850,267,253,059,899,795,996,090,799,469,201,774,624,817,718,449,867,455,659,250,178,329,070,473,119,433,165,550,807,568,221,846,571,746,373,296,884,912,819,520,317,457,002,440,926,616,910,874,148,385,078,411,929,804,522,981,857,338,977,648,103,126,085,903,001,302,413,467,189,726,673,216,491,511,131,602,920,781,738,033,436,090,243,804,708,340,403,154,190,336
What am I missing? I assume I’m missing something, because the idea of something like this going over a lot of smart programmers and developers’ heads does not sound right
What you’re looking for is probably something like certificate authentication, or mTLS. It exists, but it’s kind of a pain to set up on client devices so it’s not very common.
What’s more common and easier to set up and is nearly the same thing, is passkey authentication. Same in-flight security characteristics, but you typically need to pass a simple challenge for your device to unlock it.
There are a bunch of self-hosted auth options for both
Have you heard of ssh keys?
Barely, I’ve had to set one up for GitHub but I haven’t fully figured out what they are and what they do
ssh is a protocol that is used to log in to a computer remotely. Servers are usually administrated not by plugging a keyboard and monitor into the server, but from another machine via ssh. You can configure ssh to allow login with the same username+password you would use locally, but it is common practice to only allow authentication with an ssh key.
ssh keys allow for much higher entropy like you suggested. They are also asymmetric, and the private key can be password-protected or stored on a smartcard.
For many places, it’s operational inertia. If you’ve had a hosting account at the same place since 1998, you’re bound to still have username/password access to services like FTP even though other (and better) options exist.
And then there is the issue of sole control. Many greybeards like myself still run traditional username/password auth on services because,
- We have whitelisted our IP address, and if dynamic, keep that whitelist updated
- That outside of said whitelisting, the service is a quasi-honeypot meant to protect the machine as a whole. Any connection made from outside the address space of my ISP, by anyone else, is by default considered malicious, and is banned instantly as a precaution. They don’t even get the opportunity to attempt a login; merely connecting to said service is sufficient evidence of hostile intent.
So while my setup is not ideal, it is ideal for myself. if I had anyone else as co-admin, or even clients, things would get stupidly complicated very quickly. But since it’s just me…
I think the point here is that no-one uploads / enters a password/phrase/file.
Whatever you enter on the keyboard is hashed and the hash is sent. Depending on the protocol, sometimes it’s time limited so no-one can record the network traffic and resend the data (replay attack)
Files (SSH keys, certificates, etc) are checked against a (usually) asymetric key exchange algorithm, so they can only compare what’s sent if they have the corresponding key to decrypt the cipher.
The length of the password (or file) is basically meaningless. It’s just how long it’ll take someone to guess it (brute-force), but as the saying goes, you don’t break into a house through the door, you go through Windows… ie the weakest link.
In your concept, the weakest link is the meatware: humans. We need ease of use, so, someone will store that file and it’ll be compromised, so 64b, 128b or 512b doesn’t matter, if they have the file, they’re in.
Now… MFA… Now, that’s more like it.
If you’re talking about websites, look in to mtls
I think you are looking for SSH certificates.
I think OP is talking about auth in services that you selfhost.
For example elster.de forces you to sign in with one of the many passwordless methods, which includes: entering a username and uploading a cert file.
But most selfhosted services only have username/password logins (if any).
Yep which is why I use oauth2-proxy between these services and casdoor.
That is certificate based
That sounds like a Passkey
Nope it’s a P12 certificate
It does sound like one, but it isn’t. Ignoring the differences in UX:
Passkey
- Per-service key pair, unique per domain, Identity bound only to that specific account on that site
- Challengeresponse via WebAuthn
- Trust anchored only in the target service (no external CA)
- Private key sealed in OS / secure hardware keystore
Certificate login
- Single global identity usable across many services
- TLS client authentication with certificates
- Trust established via certificate authorities and chain validation
- Private key stored in exportable file or smartcard
Thanks for the explanation!
If a service doesnt offer Oidc, just dont self host it. The SSO service can then be properly secured and even if its only a password, at least its not reused.
Just put everything that doesn’t have OIDC behind forward auth. OIDC is overrated for selfhosting.
This is how ssh works.
That’s what SSH keys are essentially.
Or using a hardware key for physical logins.
Both of those basically make your credentials a small encrypted key file instead of password.
Usernames and passwords really only exist as a “convenience”……both for lazy users and bad actors.
I’m an admin and using an SSH key is the most common way we log into servers.
Also the most common way I log in to self-hosted servers.
SSH keys are so nice
I’ve got mine hooked into my password manager so it’s as easy as scanning my fingerprint to use (password manager locks on sleep and after a timeout).
What do you do when you need to change your fingerprints?
I have 9 backups.
After that I have to resort to crime and cryogenics.
I keep silicon based backup fingerprints in my lockbox at the credit union.
Congratulations, now your „password” (the 512-byte random key file) is stored as plaintext on your machine :)
With rate-limiting, non-trivial passwords are not viable to be brute-forced, so making them larger just doesn’t give you much.
If this is inside the threat model, you put a passphrase on that key and load it in an external process like ssh-agent or gpg-agent. Maybe even move it to a separate physical device like HSMs or crypto hardware wallets (many of which can be used for this purpose btw).
This is also neat: https://doc.qubes-os.org/en/latest/user/security-in-qubes/split-gpg-2.html#notes-about-split-gpg-2
Another one: The UX on browsers for managing password is far more developed, and the services you selfhost are accessed via a web browser.
mTLS (mutual TLS) is actually quite common out there. And SSH certificates moreso than public keys.
So clients get issued certificates that they can authenticate with. TLS for HTTPS but both ways. It sounds like this is what you’re asking about?
I have no servers that accept external password-login. All use SSH keys.
If you mean the apps you run on the servers, many can use an OAUTH server that you then host for SSO.
You can (and should) just use a password manager to generate and store ~64 byte keys which have roughly the same amount of security.
I’m always a little fearful of my password manager leaking or getting hacked, even though I use the longest password I have for it…
- You need the file everywhere. So when lunch time on work I can’t login, it is not my computer but the company machine. Yes, i have my smartphone with me I dont want to send that file to work.
- Easier with password. Easy to setup and to reuse a long password that you already have.
- My ssh server is not reachable easily. Ip restrictions goes a long way and Wireguard is good.
- Congratulations, now your work computer has access to the password (you are not as guillible to think work computer is not recording everything for the stakeholders, are you?)
