Port 584 occupies an unusual position in the Internet's addressing system. It sits in the well-known ports range (0-1023), reserved for system services that IANA officially assigns. But this port has no current assignment. It once did. It doesn't anymore.
What Lived Here
Until May 18, 2017, port 584 was officially assigned to "Key Server"—a protocol for distributing cryptographic keys across networks.12 Both TCP and UDP variants existed. The service helped solve a fundamental problem in cryptography: how do you share public keys so others can encrypt messages to you?
Keyserver protocols evolved. The more widely adopted OpenPGP HTTP Keyserver Protocol (HKP) settled on port 11371 instead.3 Whatever ran on port 584 faded into obsolescence. IANA removed the assignment, and the port became unassigned space.
The Well-Known Ports Range
Port 584 sits in the range from 0 to 1023, which the Internet Assigned Numbers Authority controls directly. These are the "well-known ports"—numbers historically reserved for fundamental Internet services. Getting an assignment here requires IETF review or IESG approval, not just an application.4
When IANA deregisters a port in this range, it doesn't immediately assign it to something else. The number sits empty. Available, but unused. A placeholder for whatever future protocol might need it.
Current Usage
No official service runs on port 584 today. That doesn't mean nothing uses it. Unofficial applications sometimes claim unassigned ports for private purposes. Remote network management tools have been observed using port 584, particularly over UDP, though these are not standardized uses.5
If you see traffic on port 584, it's either:
- An unofficial application using an unassigned port
- A legacy system still running the old Key Server protocol
- Something that shouldn't be there
Checking What's Listening
To see if anything is listening on port 584 on your system:
On Linux or macOS:
On Windows:
If something is listening and you don't recognize it, investigate. Unassigned ports sometimes attract malicious software precisely because they're not associated with known services.
Why Unassigned Ports Matter
The existence of unassigned ports reveals something true about the Internet: it evolves. Protocols that seemed essential fade away. New protocols emerge and claim different numbers. The port numbering system isn't a static allocation—it's a living document of what the Internet needs right now.
Port 584 once served a purpose. It carried cryptographic keys between systems. Then better approaches emerged, the old protocol stopped being used, and IANA quietly removed the assignment. The port returned to the pool.
This is normal. Healthy, even. The Internet reclaims numbers that aren't earning their keep. Somewhere, a future protocol will need a well-known port number. Maybe it'll be 584. Maybe the keyserver that once ran here will be completely forgotten by then.
Related Ports
- Port 11371 (TCP/UDP) — OpenPGP HTTP Keyserver Protocol (HKP), the modern standard for cryptographic key distribution
- Port 443 (TCP) — HTTPS, which now handles many key exchange operations through TLS
- Port 853 (TCP/UDP) — DNS over TLS, another protocol that handles key distribution as part of its security model
Frequently Asked Questions About Port 584
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