Port 1585 lives in the registered ports range (1024-49151), officially assigned by IANA with the service name "intv." But that name tells you almost nothing about what this port actually does.
What Actually Uses Port 1585
EMSigner uses port 1585. EMSigner is a digital signature application used primarily in India for filing GST (Goods and Services Tax) returns with a Digital Signature Certificate (DSC).12
When you install EMSigner, it runs a local web service at https://127.0.0.1:1585. Your browser connects to this local endpoint, which allows the EMSigner application to access your digital signature certificate and sign tax documents before they're submitted to government servers.
This is a common pattern: a local application runs a web server on localhost so browser-based applications can interact with hardware tokens or certificates that the browser can't access directly.
The IANA Registration Mystery
The official IANA service name is "intv," but there's no publicly available documentation explaining what "intv" stands for or what service originally registered this port. This is not uncommon in the registered ports range—many ports were assigned years ago with minimal documentation.
What matters is the current use: if you're filing GST returns in India, port 1585 needs to be available on your machine.
Security Considerations
Port 1585 appears in some security databases because malware has occasionally used this port for communication.3 But this doesn't mean the port itself is dangerous—any port can be used by malicious software.
When EMSigner uses port 1585, it binds to localhost only (127.0.0.1), which means the service is not accessible from other machines on your network. This is the correct security posture for a local signing service.
To check what's listening on port 1585:
On Linux/Mac:
On Windows:
If EMSigner is running, you'll see it bound to 127.0.0.1:1585. If you see it bound to 0.0.0.0:1585 (all interfaces), that would be unusual and worth investigating.
Related Ports
EMSigner may use multiple ports depending on version and configuration:2
- Port 1585 — Primary port for newer versions
- Port 2095 — Alternative port
- Port 2568, 2868, 4587 — Additional ports used by EMSigner components
Why Obscure Ports Matter
Port 1585 isn't famous. You won't find it in beginner networking guides. But for accountants and tax professionals in India, this port is essential infrastructure. When it doesn't work, GST filing stops.
This is the reality of the port system: most ports aren't carrying global Internet traffic. They're carrying specific, sometimes regional, sometimes industry-specific services that matter intensely to the people who depend on them.
The IANA registry says "intv." The accountant's firewall rule says "EMSigner." Both are true. The port doesn't care what you call it—it just carries the signature that makes the tax document valid.
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