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In pidgin there is a plugin that we can use to encrypt our messages in chat windows .. Is there anything simular for voip (pc to pc) ? any client that support manual encryption for voice data?(linux)

dehqan
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If you can directly connect, you can tunnel just about anything over SSL using stunnel. Any other sort of port-forwarding arrangement would also work. If you're using something more complicated involving SIP, you'll have to build a custom application or a fancier proxy that works in tandem with directory services.

I haven't used this in forever, nor has it been updated in a decade, but Speak Freely was a cool tool in its day that included crypto that the end user was responsible for. It's under the GPL.

Jeff Ferland
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Since you're mentioning Linux, if both PC's run Linux you can set up "IPSec transport" between the two systems and you'll get your manually keyed, encrypted VoIP sessions using whatever VoIP client you want!

You can also use a VPN, and I recommend using OpenVPN. VoIP works best over UDP, and OpenVPN itself uses UDP, so it can be called an UDP-friendly VPN. That said, I've used VoIP over PPTP (the kind of VPN you get for free on a Windows computer). I've mostly done that to circumvent poor routers in hotels - but I got encrypted phone conversations as a side effect. I used PPTP because it's readily available on my Android phone.

Cosmin Prund
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You can use the open-source Linphone to place secure calls. It supports:

HD Audio and video call

Secure communications (TLS, SRTP, zRTP)

You would need to use a free SIP service that supports authenticating and transporting traffic through TLS (not all do), like Linphone SIP service or Ostel.

For detailed instructions on how to set up secure calls with Linphone see:

See also:

Community
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landroni
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As far as I know Skype conversations are encrypted. It's proprietary technology and nobody knows who has which keys to it, but if I would have to guess, I'd say it's safer than SIP.

Also this page lists VOIP software that supports encryption (usually either SRTP or TLS).

Yoav Aner
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    Given your own point about Skype being proprietary, and knowing that it is controlled by Microsoft who has been forced to cooperate with the NSA, why would you speculate that it is "safer than SIP", which is an open protocol with many clients, some of which are very good and open source? – nealmcb Sep 19 '14 at 01:18
  • It's safer than SIP, because SIP is completely unencrypted by default. With SIP, you don't need to be the NSA to sniff data. Almost anybody can do it. – Yoav Aner Sep 19 '14 at 14:33
  • Most of the clients that support encryption in the page you link to do the VOIP part via SIP. But yes - with SIP you do have to make sure to use a client that supports and employs encryption, and does so effectively (not an easy thing). Whether SIP is encrypted by default depends on the client. The [SIP standard (RFC 3261 - SIP: Session Initiation Protocol)](http://tools.ietf.org/html/rfc3261) discusses how to get end-to-end security. That is something that Skype can't be trusted to do, though they do seem to provide some degree of encryption against some (but clearly not all) attackers. – nealmcb Sep 22 '14 at 22:00
  • I understand. First of all, my answer was given in Feb 2012, well-before the NSA involvement with Microsoft and other companies were discovered. Second, the vast majority of SIP clients not only do not provide encryption by default, they don't even support it. Third - the question was about clients that support encryption for voice data. The answer I gave still answers this question. I still think Skype is safer than (by-default unencrypted) SIP. And I also gave a link to alternatives to Skype. Whether or not you can trust those implementations more is beyond the scope of the question imho. – Yoav Aner Sep 24 '14 at 05:13
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In addition to other good suggestions here, you could take a look at Zfone, a system for encrypted VoIP partly designed by Phil Zimmerman (creator of PGP). See also ZRTP.

D.W.
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