Problem - Kevin Tafuro

Finally, when you’re finished using a key object, be sure to destroy the object by calling
CryptDestroyKey( ) and passing the handle to the object to be destroyed. Likewise,
when you’re done with a provider context, you must release it by calling
CryptReleaseContext( ).
See Also
Recipes 5.4, 5.17, 5.22, 5.26, 5.27, 13.2
5.26 Creating a CryptoAPI Key Object from Raw
Key Data
Problem
You have a symmetric key from another API, such as OpenSSL, that you would like
to use with CryptoAPI. Therefore, you must create a CryptoAPI key object with the
key data.
Solution
The Microsoft CryptoAPI is designed to prevent unintentional disclosure of sensitive
key information. To do this, key information is stored in opaque data objects by the
Cryptographic Service Provider (CSP) used to create the key object. Key data is
exportable from key objects, but the data must be encrypted with another key to prevent
accidental disclosure of the raw key data.
Discussion
In Recipe 5.25, we created a convenience function, SpcGetCryptContext( ), for
obtaining a handle to a CSP context object. This function uses the CRYPT_
VERIFYCONTEXT flag with the underlying CryptAcquireContext( ) function, which
serves to prevent the use of private keys with the obtained context object. To be able
to import and export symmetric encryption keys, you need to obtain a handle to a
CSP context object without that flag, and use that CSP context object for creating the
keys you wish to use. We’ll create a new function called SpcGetExportableContext( )
that will return a CSP context object suitable for creating, importing, and exporting
symmetric encryption keys.
#include
#include
HCRYPTPROV SpcGetExportableContext(void) {
HCRYPTPROV hProvider;
244 | Chapter 5: Symmetric Encryption
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