computer science

Microsoft Office password protection

Microsoft Office password protection 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 Microsoft Office password protection rather than just read about it. In short: Microsoft Office password protection is a security feature that allows Microsoft Office documents (e.g. Word, Excel, PowerPoint) to be protected with a user-provided password.

Key takeaways

Microsoft Office password protection 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 Microsoft Office password protection to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Microsoft Office password protection from memory before moving on to harder problems.

Reference excerpt

Microsoft Office password protection is a security feature that allows Microsoft Office documents (e.g. Word, Excel, PowerPoint) to be protected with a user-provided password.

Types There are two types of passwords that can be set to a document:

A password to encrypt a document restricts opening and viewing it. This is possible in all Microsoft Office applications. Since Office 2007, they are hard to break if a sufficiently complex password was chosen. If the password can be determined through social engineering, the underlying cipher is not important. Passwords that do not encrypt but restrict modification and can be circumvented. In Word and PowerPoint the password restricts modification of the entire document. In Excel passwords restrict modification of the workbook, a worksheet within it, or individual elements in the worksheet.

History of Office encryption

Weak encryptions In Excel and Word 95 and prior editions a weak protection algorithm is used that converts a password to a 16-bit verifier and a 16-byte XOR obfuscation array key. Hacking software is now readily available to find a 16-byte key and decrypt the password-protected document. Office 97, 2000, XP and 2003 use RC4 with 40 bits. The implementation contains multiple vulnerabilities rendering it insecure. In Office XP and 2003 an opportunity to use a custom protection algorithm was added. Choosing a non-standard Cryptographic Service Provider allows increasing the key length. Weak passwords can still be recovered quickly even if a custom CSP is on.

AES since Office 2007 In Office 2007, protection was significantly enhanced by using AES as a cipher. Using SHA-1 as a hash function, the password is stretched into a 128-bit key 50,000 times before opening the document; as a result, the time required to crack it is vastly increased, similar to PBKDF2, scrypt or other KDFs. Office 2010 employed AES and a 128-bit key, but the number of SHA-1 conversions doubled to 100,000. Office 2013 uses 128-bit AES, again with hash algorithm SHA-1 by default. It introduces SHA-512 hashes in the encryption algorithm, making brute-force and rainbow table attacks slower. Office 2016 uses, by default, 256-bit AES, the SHA-2 hash algorithm, 16 bytes of salt and CBC (cipher block chaining). Attacks that target the password include dictionary attacks, rule-based attacks, brute-force attacks, mask attacks and statistics-based attacks. Attacks can be sped up through multiple CPUs, also in the cloud, and GPGPU (applicable only to Office 2007-10 documents).

Excel worksheets and macro protection The protection for worksheets and macros is necessarily weaker than that for the entire workbook, as the software itself must be able to display or use them. For XLSX files that can be opened but not edited, there is another attack. As the file format is a group of XML files within a ZIP; unzipping, editing, and replacing the workbook.xml file (and/or the individual worksheet XML files) with identical copies in which the unknown key and salt are replaced with a known pair or removed altogether allows the sheets to be edited.

References

Worked examples

Example 1 — a first encounter with Microsoft Office password protection

Start with the simplest possible case. Write down what Microsoft Office password protection 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 Microsoft Office password protection 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 Microsoft Office password protection 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 Microsoft Office password protection

In research: Microsoft Office password protection 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 Microsoft Office password protection 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: Microsoft Office password protection is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cryptographic attacks, Microsoft Office, Password authentication, so understanding it makes those chapters shorter.
In everyday life: Look for Microsoft Office password protection 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 Microsoft Office password protection in 20 minutes

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

Frequently asked questions

What is Microsoft Office password protection in simple terms?

Microsoft Office password protection is a security feature that allows Microsoft Office documents (e.g. Word, Excel, PowerPoint) to be protected with a user-provided password.

Why does Microsoft Office password protection 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 Microsoft Office password protection?

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 Microsoft Office password protection.