tSIP softphone: ZRTP

ZRTP support was added in tSIP

ZRTP can be enabled in account settings:
tSIP ZRTP enable

ZRTP uses Short Authentication String (SAS) that should be compared by call parties to make sure that there is no Man-in-the-Middle attack. In default tSIP configuration SAS is visible only in log, but it can be displayed on designated buttons using script - see Tools/Script/Help/Examples, "Display ZRTP encryption state".

-- "on encryption state" script,
-- displaying ZRTP/SAS state on buttons

local btn1Id = 15	-- set this button configuration to 2 lines
local btn2Id = 16
-- end of settings

local sessionId, zrtpActive, zrtpSas, zrtpCipher, zrtpSasVerified = GetZrtpState()

print(string.format("Lua: ZRTP sessionId = %d, active = %d, SAS = %s, cipher = %s, verified = %d\n",
	sessionId, zrtpActive, zrtpSas, zrtpCipher, zrtpSasVerified))

local line1 = "ZRTP not active"
local line2 = ""
local line3 = ""

if zrtpActive == 1 then
	line1 = string.format("ZRTP SAS: %s", zrtpSas)
	if zrtpSasVerified == 1 then
		line2 = "VERIFIED"
		SetButtonImage(btn1Id, "lock_green.bmp")
		line2 = "NOT verified"
		SetButtonImage(btn1Id, "lock_yellow.bmp")
	line3 = zrtpCipher
	SetButtonImage(btn1Id, "empty.bmp")

SetButtonCaption(btn1Id, line1)
SetButtonCaption2(btn1Id, line2)
SetButtonCaption(btn2Id, line3)  

This script should be assigned to "on encryption state" scripting event. Choose two buttons for displaying text set by the script - here they are buttons #15 (for SAS and verification state display) and #16 (for cipher name). Additional bitmaps (lock_yellow.bmp, lock_green.bmp) are used visually signal that ZRTP is active but SAS is not verified and that ZRTP is active with verified SAS.
tSIP ZRTP GUI example
Two additional buttons: "Verify SAS" and "Unverify SAS" are used to store session data to file (zrtp.zid in tSIP directory) allowing to skip verification step on next call with same peer.


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