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Comment by oceanstone | Hacker News Reader

NSA harvests the entire email.

Source: http://www.wired.com/threatlevel/2007/05/mark_klein_docu/

That's obvious since the email header and body are in the same document. Presumably what's going on is they capture all emails, process them to strip off the body, and then make the headers available to the analysis systems. They can then go back and retrieve the body of any email that interests them. One of the points that critics have been making is that analysts can make the decision to retrieve the content on their own without a court order, so this whole metadata safeguard isn't much of a protection at all.

If I'm not mistaken, isn't fiber optic splitting done with a glass... Prism?

Careful, you're going down the Glenn Beck-style "OLIGARHY" route.

The person in this thread that is closest to a Fox News cast member would be the local HN government apologist. Namely, yourself.

I talked to a company that did this kind of work, and they used tiny MEMS mirrors made of gold plated silicon.

They wouldn't tell me much about their customers, but they specialized in switching and splitting high speed data at the physical layer.

http://www.glimmerglass.com/solutions/cyber-security-and-law...

"You know, in case you want a redundant signal for...redundancy...reasons."

It's done by bending the fiber, causing leaks. The signal has a single wavelength, so a prism would serve no purpose.

This makes sense. I would imagine, a prism would create a more noticeable loss of signal at the other end too since I'm guessing a splice is involved, whereas a passive leak would be less detectable.

Either way it is just refracted light, right? Same physics going on with either.

It's physics, yes, but since the light has a uniform wavelength you can't "split" the beam with a prism: you get one beam going in and only one beam going out.

Curving the cable as the other comment mentions might make sense if the curvature were calculated precisely, as then some (and not all) of the light would escape instead of being refracted back inside the cable.

My understanding is that you can use a beam splitter created from two prisms that will split laser light. This is done during holography from what I understand.

I don't entirely understand all of this, my optics is very rusty.

http://en.wikipedia.org/wiki/Beam_splitter

http://en.wikipedia.org/wiki/Holography#Apparatus

http://en.wikipedia.org/wiki/Total_internal_reflection#Fract...

Well a beam splitter as described in the Wikipedia page is moving past my own ability to describe, but the net effect from the double-prism description seems to resemble the effect of precisely curving the cable: Some light is able to internally reflect out the splitter while the rest proceeds as normal.

But in this case the prism is 'just' a convenient way of getting the desired diagonal shape with materials of different refractiveness, you're not actually breaking light into its component wavelengths as you'd see in NSA's PRISM logo.

There are several fiber optic beam splitting patents that are actual prisms which serve various needs.

For example : http://www.google.com/patents/US4671613 (one of the many). I'm not saying this is used but it does exist.

Well, a prism makes sense if you're sending multiple signals in the same fiber, and want to separate and combine the signals at the ends. The fiber connection I'm renting has two wavelengths on the same fiber.

The installation guys actually used a device to bend individual fibers during installation, to see which ones were carrying signals. Here's a similar device: http://www.tuolima.com/optical-tool-series/test-equipment/op...

I think you can also use a prism to just split 1 fiber into 2 or more, much like a mirror, similar to how some laser systems work. So in essence the original beam goes on it's merry way unaffected and the duplicate(s) goes into a black box. Though I know very little about this subject I would assume the splitter has to be exact and completely lossless. I also think there are tools to measure any interference.

For example a device like this is used to reflect fibers: http://www.ozoptics.com/ALLNEW_PDF/DTS0095.pdf

What we've seen of the slides seems to indicate that the PRISM name refers specifically to the "direct collection" from cloud-data firms (using FAA70* directives), as distinct from the "upstream collection" from the network. https://news.ycombinator.com/item?id=5887627

It's probably an optic with a coating that reflects some percentage (probably a small percentage) of the light, and a second detector.

http://www.edmundoptics.com/optics/beamsplitters/

We use these extensively:

http://vssmonitoring.com/products/traditional_tap.asp

I'm not sure how they work, but the sales engineer said "mirrors". The fibre units are completely passive.

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