Detect if the connection is possible via a secure channelTag(s): Varia
If the appVersion (or the userAgent) property end with ;U which designates USA/Canada, the browser has the 128-bit strong encryption.
for (i in navigator) alert(i + " = " + navigator[i])
If the property ends with ";I" which designates International, then the browser _probably_ does not.
Note: for a java solution see this HowTo
var encryption = navigator.appName != 'Netscape' ? 'unknown' : navigator.userAgent.indexOf(' U') != -1 ? 'strong' : 'weak';