Re: Decrypting on different platforms

From: Ryan Menezes [MSFT] (ryanmen_at_online.microsoft.com)
Date: 05/26/05 

Date: Thu, 26 May 2005 08:54:41 -0700

CryptGetUserKey failure is expected since you never created an asymmetric
key using CryptGenKey in the first place.
When creating the RC2 key, also look into specifying the KP_EFFECTIVE_KEYLEN
flag using CryptSetKeyParam().

Thanks,
Ryan Menezes [MSFT] 

-- 
This posting is provided "AS IS" with no warranties, and confers no rights. 
"Use of included script samples are subject to the terms specified at 
http://www.microsoft.com/info/cpyright.htm"
"Frank Perry" <FrankPerry@discussions.microsoft.com> wrote in message 
news:06E49322-EE75-4623-B548-42555EE61558@microsoft.com...
> Howdy,
>
> I am using the built in CSP.
>
> The code is lifted from the eMbedded Visual C++ help for encrypting and
> decrypting data.  Here are the sections that give me trouble.
>
> // Get the handle to the default provider.
>  if (!CryptAcquireContext (&hProv, NULL, NULL, PROV_RSA_FULL, 0))
>  {
>    wprintf (TEXT("Error %x during CryptAcquireContext!\n"),
>             GetLastError ());
>    goto exit;
>  }
>
>  if (lpszPassword == NULL)
>  {
>    // Encrypt the file with a random session key.
>
>    // Create a random session key.
>    if (!CryptGenKey (hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey))
>    {
>      wprintf (TEXT("Error %x during CryptGenKey!\n"),
>               GetLastError ());
>      goto exit;
>    }
>
>    // Get the handle to the key exchange public key.
>    if (!CryptGetUserKey (hProv, AT_KEYEXCHANGE, &hXchgKey))
>    {
>      wprintf (TEXT("Error %x during CryptGetUserKey!\n"),
>               GetLastError ());
>      goto exit;
>    }
> This is the path with no password.  Here it should be giving me a key that 
> I
> can export to a blob and then save someplace.  At this point, it always 
> fails
> saying there is no key.
>  ***
>  }
>  else
>  {
>    // Encrypt the file with a session key derived from a password.
>
>    // Create a hash object.
>    if (!CryptCreateHash (hProv, CALG_MD5, 0, 0, &hHash))
>    {
>      wprintf (TEXT("Error %x during CryptCreateHash!\n"),
>               GetLastError ());
>      goto exit;
>    }
>
>    // Hash in the password data.
>    if (!CryptHashData (hHash, (PBYTE)lpszPassword,
>                        wcslen (lpszPassword), 0))
>    {
>      wprintf (TEXT("Error %x during CryptHashData!\n"),
>               GetLastError ());
>      goto exit;
>    }
>
>    // Derive a session key from the hash object.
>    if (!CryptDeriveKey (hProv, CALG_RC2, hHash, 0, &hKey))
>    {
>      wprintf (TEXT("Error %x during CryptDeriveKey!\n"),
>               GetLastError ());
>      goto exit;
>    }
>  }
>
> If I give it a pass word, this section works fine but the same pass word 
> on
> the CE machine does not work on the W2K machine.  It does work on a 
> different
> CE machine.  (I have converted both to bytes so the CE machine is not
> encrypting Unicode.)
>
> For the first example, I have tried running it on both the systems and get
> the same failure.  My current thinking is that the is a security setting 
> at
> the OS level that is preventing me from exporting a key.  If so, the 
> sample
> code should say something about it, but doesn't.
>
> For the second, I have looked at the hash and found the hash was different
> between the machines.  I took the hash from one machine and force the hash 
> in
> the other machine to the same value.  But that didn't help.  I would force
> the key but I can't get an exportable key.
>
> Any ideas?  As I said, I'm looking at the security settings to see if 
> there
> is something that could block me from making an exportable key.
> -- 
> Frank Perry
> LavaLeaf Software
>
>
> "Ryan Menezes [MSFT]" wrote:
>
>> Which encryption algorithm are you using and what are the default CSPs on
>> those machines ?
>>
>> Would definetely help if you can post some sample code.
>>
>> Thanks,
>> Ryan Menezes [MSFT]
>>
>> -
>> This posting is provided "AS IS" with no warranties, and confers no 
>> rights.
>> "Use of included script samples are subject to the terms specified at
>> http://www.microsoft.com/info/cpyright.htm"
>>
>>
>>
>> "Frank Perry" <FrankPerry@discussions.microsoft.com> wrote in message
>> news:03189DBD-7470-4C7A-97D3-50F68764BCED@microsoft.com...
>> > Howdy,
>> >
>> > I forgot to mention that I have both machines using 40 bit key lengths.
>> >
>> > -- 
>> > Frank Perry
>> > LavaLeaf Software
>> >
>> >
>> > "Frank Perry" wrote:
>> >
>> >> Howdy,
>> >>
>> >> I have been using the sample code for encrypting and decrypting files. 
>> >> I
>> >> have no trouble using the password version to encrypt a file and 
>> >> decrypt
>> >> it
>> >> on the same machine.  But when I move the file to a different machine
>> >> with a
>> >> different OS, it fails.  The two OSs are W2K and CE.
>> >>
>> >> So far, I have found the the hash created from the same password is
>> >> different on the two machines.  I have tried forcing the same hash on
>> >> both
>> >> machines but that doesn't get me anywhere either.  I haven't seen the 
>> >> CE
>> >> side, but the KP_IV of the W2K side is all 0's.
>> >>
>> >> I would try transfering the key itself, but on a different problem, I
>> >> can't
>> >> get CryptGetUserKey to return a key.  I am using the code from the
>> >> example
>> >> but nothing comes back.  I get the error that there is no key.
>> >>
>> >> Are there any ideas about either of these problems?
>> >>
>> >> Thanks in advance.
>> >> -- 
>> >> Frank Perry
>> >> LavaLeaf Software
>>
>>
>>

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