computer science

Protected Streaming

Protected Streaming is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Protected Streaming rather than just read about it. In short: Protected Streaming is a DRM technology by Adobe. The aim of the technology is to protect digital content (video or audio) from unauthorized use.

Key takeaways

Protected Streaming belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Protected Streaming to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Protected Streaming from memory before moving on to harder problems.

Reference excerpt

Protected Streaming is a DRM technology by Adobe. The aim of the technology is to protect digital content (video or audio) from unauthorized use. Protected Streaming consists of many different techniques; basically there are two main components: encryption and SWF verification. This technique is used by the Hulu desktop player and the RTÉ Player. Fifa.com also uses this technique to serve the videos on the official site. Some videos on YouTube also use RTMPE, including those uploaded there by BBC Worldwide.

Encryption Streamed content is encrypted by the Flash Media Server "on the fly", so that the source file itself does not need to be encrypted (a significant difference from Microsoft's DRM). For transmission ("streaming"), a special protocol is required, either RTMPE or RTMPS. RTMPS uses SSL-encryption. In contrast, RTMPE is designed to be simpler than RTMPS, by removing the need to acquire a SSL Certificate. RTMPE makes use of well-known industry standard cryptographic primitives, consisting of Diffie–Hellman key exchange and HMACSHA256, generating a pair of RC4 keys, one of which is then used to encrypt the media data sent by the server (the audio or video stream), while the other key is used to encrypt any data sent to the server. RTMPE caused less CPU-load than RTMPS on the Flash Media Server. Tools which have a copy of the well-known constants extracted from the Adobe Flash Player are able to capture RTMPE streams, a form of the trusted client problem. Adobe issued DMCA takedowns on RTMPE recording tools, including rtmpdump, to try to limit their distribution. In the case of rtmpdump, however, this led to a Streisand effect.

SWF verification The Adobe Flash Player uses a well-known constant, appended to information derived from the SWF file (a hash of the file and its size), as input to HMACSHA256. The HMACSHA256 key is the last 32 bytes of the server's first handshake packet. The Flash Media Server uses this to limit access to those clients which have access to the SWF file (or have been given a copy of the hash and the size of the SWF file). All officially allowed clients (which are in fact *.swf files) need to be placed on the Flash Media Server streaming the file. Any other client requesting a connection will receive a "connection reject". The combination of both techniques is intended to ensure streams cannot be sniffed and stored into a local file, as SWF verification is intended to prevent third party clients from accessing the content. However, it does not achieve this goal. Third party clients are free to write the decrypted content to a local file simply by knowing the hash of the SWF file and its size. In practice, therefore, Adobe's own implementation of the Macromedia Flash Player is the only client which does not allow saving to a local file. The only possible way to restrict connections to a Flash Media Server is to use a list of known hosts, to avoid the whole player (the Flash client) being placed on an unauthorised website. Even this has no real benefit for mass-distributed files, as any one of the known hosts could take a copy of the data and re-distribute it at will. Thus "known host" security is only useful when the known hosts can be trusted not to re-distribute the data.

Notes

References Whitepaper by Adobe RTMPE (Adobe LiveDocs) RTMPS (Adobe LiveDocs) RTMFP encryption mechanism (DRAFT), reverse engineered from scratch

Worked examples

Example 1 — a first encounter with Protected Streaming

Start with the simplest possible case. Write down what Protected Streaming claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Protected Streaming before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Protected Streaming ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Protected Streaming

In research: Protected Streaming appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Protected Streaming in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Protected Streaming is common in secondary-school and first-year university syllabi. It links to neighbouring topics Multimedia, Network protocols, so understanding it makes those chapters shorter.
In everyday life: Look for Protected Streaming outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Protected Streaming in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Protected Streaming means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Protected Streaming out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Protected Streaming in simple terms?

Protected Streaming is a DRM technology by Adobe. The aim of the technology is to protect digital content (video or audio) from unauthorized use.

Why does Protected Streaming matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Protected Streaming?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Protected Streaming.