computer science

Microsoft CryptoAPI

Microsoft CryptoAPI 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 CryptoAPI rather than just read about it. In short: The Microsoft Windows platform specific Cryptographic Application Programming Interface (also known variously as CryptoAPI, Microsoft Cryptography API, MS-CAPI or simply CAPI) is an application programming interface included with Microsoft Windows operating systems that provides services to enable developers to secure Windows-based applications using cryptography. It is a set of dynamically linked libraries that pro…

Key takeaways

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

Reference excerpt

The Microsoft Windows platform specific Cryptographic Application Programming Interface (also known variously as CryptoAPI, Microsoft Cryptography API, MS-CAPI or simply CAPI) is an application programming interface included with Microsoft Windows operating systems that provides services to enable developers to secure Windows-based applications using cryptography. It is a set of dynamically linked libraries that provides an abstraction layer which isolates programmers from the code used to encrypt the data. The Crypto API was first introduced in Windows 95 OSR2 and Windows NT 4.0 and enhanced in subsequent versions. CryptoAPI supports both public-key and symmetric key cryptography, though persistent symmetric keys are not supported. It includes functionality for encrypting and decrypting data and for authentication using digital certificates. It also includes a cryptographically secure pseudorandom number generator function: CryptGenRandom. CryptoAPI works with a number of CSPs (Cryptographic Service Providers) installed on the machine. CSPs are the modules that do the actual work of encoding and decoding data by performing the cryptographic functions. Vendors of HSMs may supply a CSP which works with their hardware.

Cryptography API: Next Generation Windows Vista features an update to the Crypto API known as Cryptography API: Next Generation (CNG). It has better API factoring to allow the same functions to work using a wide range of cryptographic algorithms, and includes a number of newer algorithms that are part of the National Security Agency (NSA) Suite B. It is also flexible, featuring support for plugging custom cryptographic APIs into the CNG runtime. However, CNG Key Storage Providers still do not support symmetric keys. CNG works in both user and kernel mode, and also supports all of the algorithms from the CryptoAPI. The Microsoft provider that implements CNG is housed in Bcrypt.dll. CNG also supports elliptic curve cryptography which, because it uses shorter keys for the same expected level of security, is more efficient than RSA. The CNG API integrates with the smart card subsystem by including a Base Smart Card Cryptographic Service Provider (Base CSP) module which encapsulates the smart card API. Smart card manufacturers just have to make their devices compatible with this, rather than provide a from-scratch solution. CNG also adds support for Dual_EC_DRBG, a pseudorandom number generator defined in NIST SP 800-90A that could expose the user to eavesdropping by the National Security Agency since it contains a kleptographic backdoor, unless the developer remembers to generate new base points with a different cryptographically secure pseudorandom number generator or a true random number generator and then publish the generated seed in order to remove the NSA backdoor. It is also very slow. It is only used when called for explicitly. CNG also replaces the default PRNG with CTR_DRBG using AES as the block cipher, because the earlier RNG which is defined in the now superseded FIPS 186-2 is based on either DES or SHA-1, both which have been broken. CTR_DRBG is one of the two algorithms in NIST SP 800-90 endorsed by Schneier, the other being Hash_DRBG.

See also CAPICOM DPAPI Encrypting File System Public-key cryptography Cryptographic Service Provider PKCS#11 Crypto API (Linux)

References

External links Cryptography Reference on MSDN Microsoft CAPI at CryptoDox

Worked examples

Example 1 — a first encounter with Microsoft CryptoAPI

Start with the simplest possible case. Write down what Microsoft CryptoAPI 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 CryptoAPI 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 CryptoAPI 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 CryptoAPI

In research: Microsoft CryptoAPI 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 CryptoAPI 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 CryptoAPI is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cryptographic software, Microsoft Windows security technology, Microsoft application programming interfaces, so understanding it makes those chapters shorter.
In everyday life: Look for Microsoft CryptoAPI 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 CryptoAPI in 20 minutes

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

Frequently asked questions

What is Microsoft CryptoAPI in simple terms?

Why does Microsoft CryptoAPI 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 CryptoAPI?

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 CryptoAPI.