When I try to connect to a new install of UltraVNC I get a message saying "authentication rejection".
In the new install I do have my rc4.key that I have used for many years.
I also have:
20121120_Server_ClientAuth.pubkey
20121120_Viewer_ClientAuth.pkey
All three files are in the same folder that UltraVNC is installed in.
Years ago I think I remember the rc4.key had to be included in the config but I don't see a way to do that now.
What do I need to do to get it recognized?
Thank you,
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Development: UltraVNC development is always here... Any help is welcome
Feedback is welcome
A new stable version, UltraVNC 1.6.4.0 and UltraVNC SC 1.6.4.0 have been released: https://forum.uvnc.com/viewtopic.php?t=38095
Feedback is always welcome
2026-03-11: CVE-2026-3787 Clarification: https://forum.uvnc.com/viewtopic.php?t=38155
2025-12-14: 1.7.1.X-dev release builds need tests and feedback: https://forum.uvnc.com/viewtopic.php?t=38134
2025-12-02: We need help: English Wikipedia UltraVNC page has been requested to deletion: https://forum.uvnc.com/viewtopic.php?t=38127
Any help is welcome to improve the UltraVNC page and/or to comment on the Wikipedia Talk page
2025-05-06: Forum password change request: https://forum.uvnc.com/viewtopic.php?t=38078
2023-09-21: Important: Please update to latest version before to create a reply, a topic or an issue: https://forum.uvnc.com/viewtopic.php?t=37864
Development: UltraVNC development is always here... Any help is welcome
Feedback is welcome
authentication rejection
- Rudi De Vos
- Admin & Developer

- Posts: 6992
- Joined: 2004-04-23 10:21
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Re: authentication rejection
rc4 is the key for the old encryption module (MSRC4Plugin).
The new encryption (SecureVNC Plugin) uses
- 20121120_Server_ClientAuth.pubkey
- 20121120_Viewer_ClientAuth.pkey
On the UltraVNC Viewer and UltraVNC Server you need to select to use the SecureVNC Plugin:
- 20121120_Server_ClientAuth.pubkey need to be in the folder where you start winvnc.exe
- 20121120_Viewer_ClientAuth.pkey need to be copied to the UltraVNC Viewer PC, in the folder of vncviewer.exe
See also:
- https://uvnc.com/docs/documentation-1-3 ... ption.html
The new encryption (SecureVNC Plugin) uses
- 20121120_Server_ClientAuth.pubkey
- 20121120_Viewer_ClientAuth.pkey
On the UltraVNC Viewer and UltraVNC Server you need to select to use the SecureVNC Plugin:
- 20121120_Server_ClientAuth.pubkey need to be in the folder where you start winvnc.exe
- 20121120_Viewer_ClientAuth.pkey need to be copied to the UltraVNC Viewer PC, in the folder of vncviewer.exe
See also:
- https://uvnc.com/docs/documentation-1-3 ... ption.html
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- Website: https://uvnc.com/
- Forum: https://forum.uvnc.com/
- GitHub sourcecode: https://github.com/ultravnc/UltraVNC
- Mastodon: https://mastodon.social/@ultravnc
- Bluesky/AT Protocol: https://bsky.app/profile/ultravnc.bsky.social
- Facebook: https://www.facebook.com/ultravnc1
- X/Twitter: https://x.com/ultravnc1
- Reddit community: https://www.reddit.com/r/ultravnc
- OpenHub: https://openhub.net/p/ultravnc
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