science

Rpmsg

Rpmsg is a 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 Rpmsg rather than just read about it. In short: An rpmsg file is a file format containing a restricted-permission message. It is used to implement IRM for Outlook messages with the aim of controlling access to content via encryption and access controls, and restricting certain actions such as the ability to forward or copy.

Key takeaways

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

Reference excerpt

An rpmsg file is a file format containing a restricted-permission message. It is used to implement IRM for Outlook messages with the aim of controlling access to content via encryption and access controls, and restricting certain actions such as the ability to forward or copy. Messages in this format are normally created by users of Azure Information Protection, Azure Rights Management or Active Directory Rights Management Services.

Implementation The rpmsg file is created by writing body, attachments and images to a compound file and then compressing and encrypting it to create a BLOB: the rpmsg file. This resulting file is named message.rpmsg and is included as an attachment to a normal Outlook message. Applications that support this format, such as Microsoft Outlook, transparently extract and render the message contained in the attachment as a protected message, ignoring the MIME wrapper message that hosts it. This can be implemented by parsing the file structure in-code, as currently the MSIPC SDK, normally used by applications to protect and decrypt content protected with Azure Information Protection, does not provide native functionality to encode and decode the RPMSG format. Other applications such as mobile mail clients rely on Exchange ActiveSync to perform decryption on their behalf and deliver a version of the message they can render directly.

Rights control When a rights managed mail is created the author specifies what rights they wish to grant to the recipient and these rights are specified in the form of an XrML certificate called a 'Publishing License'. This certificate is included within the encrypted rpmsg file. When the rpmsg attachment is decrypted the enclosed 'Publishing License' is sent to the information protection service pointed to by its header in order to obtain a Use License. The service, after analyzing the policy in the certificate and matching it to the identity of the requestor, will build the Use License, another XrML encoded document, which will then be delivered to the client and used by Outlook to determine what the recipient can and cannot do with the message (rights to forward, copy etc.).

File format An rpmsg file consists of a magic number followed by one or more data chunks. The magic number is the eight-byte sequence 76 e8 04 60 c4 11 e3 86. Each data chunk consists of a 12-byte header followed by a variable amount of data bytes. The chunk header consists of 3 DWORDS in little-endian byte order:

Magic number a0 0f 00 00 Uncompressed chunk length YY YY YY YY Compressed chunk length XX XX XX XX. The chunk body consists of X bytes of compressed data. The concatenated data chunks form a single data stream compressed using the DEFLATE algorithm. The format of the uncompressed data is a Compound File Binary document. More specifically, the uncompressed data conforms to the Office Document Cryptography Structure format.

References

External links Official page for Azure Information Protection Compound File Binary File Format

Worked examples

Example 1 — a first encounter with Rpmsg

Start with the simplest possible case. Write down what Rpmsg claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Rpmsg 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 Rpmsg 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 Rpmsg

In research: Rpmsg appears in 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 Rpmsg 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: Rpmsg is common in secondary-school and first-year university syllabi. It links to neighbouring topics Digital rights management, Microsoft Office, so understanding it makes those chapters shorter.
In everyday life: Look for Rpmsg 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Rpmsg in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rpmsg 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 Rpmsg out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rpmsg in simple terms?

Why does Rpmsg matter?

Because it connects several 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 Rpmsg?

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 Rpmsg.