createKeyFromHMACSecretBinary Method

Article
10/27/2016

[This feature was implemented for MSXML 5.0 for Microsoft Office Applications. XML digital signatures are not supported in MXSML 6.0 and later.]

Extracts a key from a binary HMAC secret value for use by C/C++ applications.

C/C++ Syntax Using Smart Pointers

IXMLDSigKeyPtr objKey=  
oXMLDigitalSignature->createKeyFromHMACSecretBinary(  
   (byte*)secret,   
   (LONG)lSecretLen,   
   (LONG)lHMACOutputLength);

C/C++ Syntax

HRESULT createKeyFromHMACSecretBinary(  
    CONST byte* secret,  
    LONG lSecretLen,  
    LONG lHMACOutputLength,  
    IXMLDSigKey** keyObj);

Parameters

secret[in]
Binary HMAC secret value.

lSecretLen[in]
Length of the binary HMAC secret value in bytes.

lHMACOutputLength[in]
Number of bits used to represent the secret value for signing or verify. The value of this parameter corresponds to the content of the <ds:HMACOutputLength> element in <ds:Signature>. It can be a positive number in multiples of eight (8), or negative one (-1).

The following table explains the meanings of the different possible values of lHMACOutputLength.

value	Meaning
Positive number	Bit length of the secret value. Must be in multiples of eight (8). If the length of the given secret value is longer than this number, it will be truncated to this number when signing.
-1	Use the content of `<ds:HMACOutputLength>` element from the containing `<ds:SignatureMethod>` element.

objKey[out, retval]
In C/C++ this is the reference to the resultant key object that implements the IXMLDSigKey interface. In C/C++ with smart pointer class wrappers, this is the resultant key object.

Return Values

The method returns the standard HRESULT values defined in the CryptoAPI, including the following:

S_OK
The value returned if successful.

E_FAIL
The value returned if there was insufficient information, if the method call was not authorize, etc.

Remarks

This method has the same behavior as the createKeyFromHMACSecret method, except that it takes a binary as the HMAC secret value and it can only called from a C/C++ application.

Example

This example illustrates how to use the createKeyFromHMACSecretBinary method to generate a key for signing and verifying data referenced in an XML digital signature. This example is similar to the createKeyFromHMACSecret Method example. The difference is that the binary value of the HMAC secret ("secret") is used, instead of the base64 encoded value ("c2VjcmV0"). The two examples use the same resource file, and their output is identical.

Applies to

IXMLDigitalSignatureEx

Versioning

MSXML 5.0 for Microsoft Office Applications and later

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