problem with CryptGetKeyParam()

[hahaha]

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I'm using CryptGen key to generate keys of specific length but when i call CryptGetKeyParam to print the length of the key it doesnt show.
actually i give user choices of keylength in a combo box whos variable is passed in the CryptGenKey function.
The code is like

int m_keysize; //member variable of combo box

if (!CryptGenKey(hCryptProv, AT_SIGNATURE,DWORD(m_keysize), &hKey))
{
// Error during CryptGenKey!

}

if(CryptGetKeyParam(
hKey,
KP_KEYLEN,
pbData,
&dwCount,
0))
{
MessageBox((LPCTSTR)pbData,"Key size",MB_OK);
}


All the variables are declared and keys are successfully generated as well.but the key length is not shown in the message box i.e empty message box

[olivthill]

The syntax of CryptGetKeyParam() can be seen at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/seccrypto/security/cryptgetkeyparam.asp

...
KP_KEYLEN Retrieve the actual length of the key. The pbData parameter is a pointer to a DWORD value that receives the key length, in bits. KP_KEYLEN can be used to get the length of any key type. Microsoft cryptographic service providers (CSPs) return a key length of 64 bits for CALG_DES, 128 bits for CALG_3DES_112, and 192 bits for CALG_3DES. These lengths are different from the lengths returned when you are enumerating algorithms with the dwParam value of the CryptGetProvParam function set to PP_ENUMALGS. The length returned by this call is the actual size of the key, including the parity bits included in the key.
Microsoft CSPs that support the CALG_CYLINK_MEK ALG_ID return 64 bits for that algorithm. CALG_CYLINK_MEK is a 40-bit key but has parity and zeroed key bits to make the key length 64 bits.
...

So, since pbData is a pointer to a DWORD, not a pointer to a string of characters, you have to convert the value before displaying it in your MessageBox.

[hahaha]

if(CryptGetKeyParam(
hKey,
KP_KEYLEN,
NULL,
&dwCount,
0))
{
// Allocate memory for the pbData.
if(pbLen = (BYTE*)malloc(dwCount))
{
MessageBox("Memory has been allocated for the blob.");
}
else
{
MessageBox("Out of memory.");
}
}

if(CryptGetKeyParam(
hKey,
KP_KEYLEN,
pbLen,
&dwCount,
0))
{
MessageBox((LPCTSTR)pbLen,"Key size",MB_OK);
}

here i do like this but it still doesnt show the length of the key

[olivthill]

The problem is still in the line

MessageBox((LPCTSTR)pbLen,"Key size",MB_OK);

pbLen is not a pointer to an array containing nice and sociable visible digits, but it contains your value as a compact and shy binary number. You have to convert it, so that you will see it. For instance, you can do:

char msgbuf[100];
sprintf(msgbuf, "%d", pbLen);
MessageBox(msgbuf,"Key size",MB_OK);

[hahaha]

char msgbuf[100];
sprintf(msgbuf, "%d", pbLen);
MessageBox(msgbuf,"Key size",MB_OK);


Ive used this code..but in the msg box I get values like "7805163"...what this mean....even I've set the key length for RSA as 512 bits.