BCRYPT_DH_PARAMETER_HEADER structure (bcrypt.h)

Article
02/22/2024

The BCRYPT_DH_PARAMETER_HEADER structure is used to contain parameter header information for a Diffie-Hellman key. This structure is used with the BCRYPT_DH_PARAMETERS property in the BCryptSetProperty function.

Syntax

typedef struct _BCRYPT_DH_PARAMETER_HEADER {
  ULONG cbLength;
  ULONG dwMagic;
  ULONG cbKeyLength;
} BCRYPT_DH_PARAMETER_HEADER;

Members

cbLength

The total size, in bytes, of this structure and the buffer that immediately follows this structure in memory.

dwMagic

The magic value for the key.

This member must be the following value.

BCRYPT_DH_PARAMETERS_MAGIC (0x4d504844)

cbKeyLength

The size, in bytes, of the key that this structure applies to.

Remarks

This structure is used as a header for a larger buffer. The single memory block consists of this structure followed by a buffer of cbKeyLength size that contains the Diffie-Hellman prime number, and another buffer of cbKeyLength size that contains the Diffie-Hellman generator number. Both of these numbers are in big-endian format.

The following example shows how to calculate the sizes needed for this buffer and how to fill in the members of this structure.

// In this example, the rgbModulus variable is a byte array that contains the modulus in big-endian byte order. 
// The rgbGenerator variable is a byte array that contains the generator in big-endian byte order.

ULONG cbDHParams = sizeof(BCRYPT_DH_PARAMETER_HEADER) +     (cbKeySize * 2);
PBYTE pbDHParams = (PBYTE)malloc(cbDHParams);
if(!pbDHParams)
{
    status = STATUS_NO_MEMORY;
    goto Cleanup;
}

BCRYPT_DH_PARAMETER_HEADER *pDHParamHeader;
pDHParamHeader = (BCRYPT_DH_PARAMETER_HEADER*)pbDHParams;
pDHParamHeader->cbLength = cbDHParams;
pDHParamHeader->cbKeyLength = cbKeySize;
pDHParamHeader->dwMagic = BCRYPT_DH_PARAMETERS_MAGIC;

// Add the modulus to the parameters.
// The rgbModulus argument is a byte array that contains the modulus.
PBYTE pbTemp = (PBYTE)pbDHParams + sizeof(BCRYPT_DH_PARAMETER_HEADER);
CopyMemory(pbTemp, rgbModulus, pDHParamHeader->cbKeyLength);

// Add the generator to the parameters.
// The rgbGenerator argument is a byte array that contains the generator.
pbTemp += pDHParamHeader->cbKeyLength;
CopyMemory(pbTemp, rgbGenerator, pDHParamHeader->cbKeyLength);

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 [desktop apps only]
Header	bcrypt.h