CryptHashPublicKeyInfo

The CryptHashPublicKeyInfo function encodes the public key information and computes its hash.

#include <wincrypt.h>
BOOL WINAPI CryptHashPublicKeyInfo(
  HCRYPTPROV hCryptProv,        // in
  ALG_ID Algid,                 // in
  DWORD dwFlags,                // in
  DWORD dwCertEncodingType,     // in
  PCERT_PUBLIC_KEY_INFO pInfo,  // in
  BYTE *pbComputedHash,         // out
  DWORD *pcbComputedHash        // in, out
);
 

Parameters

hCryptProv

Specifies the Cryptographic Service Provider to use to compute the hash.

Unless there is a strong reason for passing in a specific cryptographic provider in hCryptProv, zero should be passed in. Passing in zero causes the default RSA or DSS provider to be acquired before doing hash, signature verification or recipient encryption operations.

Algid

Specifies the CryptoAPI hash algorithm to use. If Algid is zero, the default hash algorithm, SHA1, is used.

dwFlags

Normally zero. Gets passed on to CryptCreateHash.

dwCertEncodingType

The type of encoding used on the certificate. Currently defined certificate encoding types are shown in the following table:

Encoding type	Value
X509_ASN_ENCODING	0x00000001

pInfo

A pointer to the public key information to be encoded and hashed.

pbComputedHash

Pointer to a buffer that receives the computed hash.

This parameter can be NULL to set the size of this information for memory allocation purposes. For more information, see Common In/Out Parameter Conventions.

pcbComputedHash

Pointer to a DWORD that contains the size, in bytes, of the buffer pointed to by the pbComputedHash parameter. When the function returns, the variable pointed to by the pcbComputedHash parameter contains the number of bytes stored in the buffer. This parameter can be NULL only if pbComputedHash is NULL.

Note  When processing the data returned in the buffer, applications need to use the actual size of the data returned. The actual size may be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to insure that the largest possible output data will fit in the buffer.) On output, the variable pointed to by this parameter is updated to reflect the actual size of the data copied to the buffer.

Return Values

TRUE if the function succeeded, FALSE if the function failed.

Call GetLastError to see the reason for any failures. Note that errors from the called functions CryptCreateHash, CryptGetHashParam and CryptHashData may be propagated to this function. This function has the following error codes.

Example

// EXAMPLE CODE FOR USING CryptHashPublicKeyInfo().
// Encodes the public key information and computes its hash.
// Assume that a pointer to the Public Key blob (pInfo) has 
// already been defined.

// Set up the variables.
HCRYPTPROV hCryptProv = 0;    // Service Provider handle- normally 0
ALG_ID Algid = 0;             // Algorithm
DWORD dwFlags = 0;            // Flags value- normally 0
DWORD dwCertEncodingType = X509_ASN_ENCODING;
                              // Type of encoding
PCERT_PUBLIC_KEY_INFO pInfo;  // Pointer to public key info 
BYTE * pbComputedHash;        // Pointer to computed hash
DWORD cbComputedHash;         // Size of computer hash
BOOL fResult;                 // Return TRUE if function succeeded
                              //   FALSE if function failed

// Function called the first time to get
// the size of the returned hash.
fResult= CryptHashPublicKeyInfo(
           hCryptProv,
           Algid,
           dwFlags,
           dwCertEncodingType,
           pInfo,
           NULL,              // NULL on first call
                              //   NULL is used to determine the
                              //   size needed to insure that the
                              //   returned data fits in the
                              //   specified buffer
           &cbComputedHash);

if (!fResult){
  cout<< "first call to CryptHashPublicKeyInfo failed"<< endl;
}
else {
  cout<< "first call to CryptHashPublicKeyInfo successful"<< endl;
  pbComputedHash = (BYTE *)malloc (cbComputedHash);
  cout<< "memory allocated"<< endl;
}

// Function call to get the computed hash
fResult= CryptHashPublicKeyInfo(
           hCryptProv,        // in - 0 is default RSA or DSS provider 
           Algid,             // in - 0 is default 
           dwFlags,           // in - set to 0
           dwCertEncodingType,// in - X509_ASN_ENCODING
           pInfo,             // in - Public key info
           pbComputedHash,    // out- Pointer to the returned hash 
           &cbComputedHash);  // in/out - Size of hash

if (!fResult) {               // FALSE
 cout<< "Function failed"<< endl
     << "error = "<< GetLastError()<< endl;
}
else {                        // TRUE
 cout<< "Function succeeded"<< endl;
}
free (pInfo);
 

QuickInfo

  Windows NT: Requires version 4.0 SP3 or later. Available also in IE 3.02 and later.
  Windows: Requires Windows 98 (or Windows 95 with IE 3.02 or later).
  Windows CE: Unsupported.
  Header: Declared in wincrypt.h.
  Import Library: Use crypt32.lib.

See Also

CryptHashCertificate, CryptHashToBeSigned