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
It's a pain to manage. If you want to change it, you have to go to each server and update it manually, if you don't already have automation. If you do have automation, that's another thing you have to set up and manage. And all that for not much gain.
Not if you use certificates signed by your own internal CA and trust the CA instead of straight up trusting the public keys explicitly.
This way you can generate new SSH or TLS keys trusted across a bunch of machines without having to touch those machines directly for every key, since they are signed by your trusted authority. If you configure CRLs properly you can also revoke them centrally.
Hosting a CA is a whole additional service to set up, as is enabling trust for said CA on every server you're running.
A CA can be an encrypted volume on a live USB stick. It's mostly for the CRLs you might want something online. A static HTTP server where you manually dump revocations is enough for that.
Unless you do TOFU (which some do and btw how often do you actually verify the github.com ssh fingerprint when connecting from a new host?), you need to add the trust root in some way, just as with any other method discussed. But that's no more work than doing the same with individual host keys.
And what's the alternative? Are you saying it's less painful to log in and manually change passwords for every single server/service when you need to rotate?