You need to look at your data to see how the bytes are swapped:
3 common patterns:
1) Even odd bytes are swapped
2) The data was treated as 32 bit, one system is little ended and the
other big ended.
3) The entire buffer is reversed.
Assume pcBuffer is the char * pointer to your data, uiLen is the
unsigned length of the data.
For 1)
char acTemp = new char[ uiLen ];
_swab(pcBuffer,acTemp,uiLen);
memcpy(pcBuffer,acTemp,uiLen);
delete acTemp;
Note: uiLen is assumed to be even
For 2)
char cTemp;
int i,j;
for (i=0;i<uiLen;i+=4)
{
for (j=0;j<2;j++)
{
cTemp = pcBuffer[ i+j];
pcBuffer[ i+j ] = pcBuffer[ i+3-j ];
pcBuffer[ i+3-j] = cTemp;
}
Note: This code assumes that uiLen is a multiple of 4;
For 3)
char cTemp;
for (i=0;i<uiLen/2;i++)
{
cTemp = pcBuffer[ i];
pcBuffer[ i ] = pcBuffer[ i+uiLen-i-1 ];
pcBuffer[ i+uiLen-i-1] = cTemp;
}
Carter
Carter Browne
CBCS
cbro...@cbcs-usa.com
781-721-2890
Goblin_Queen wrote:
> Yes, I know that, but I don't know how to do that in code. I've found the
> following post:
> http://stackoverflow.com/questions/105252/how-do-i-convert-between-big-endian-and-little-endian-values-in-c
> http://stackoverflow.com/questions/105252/how-do-i-convert-between-big-endian-and-little-endian-values-in-c
>
> where I've tried the method with the template<>, which definitely didn't
> give me a correct result.
> On that forum they're saying that char's don't have to be converted, but is
> that true?
>
> Would it be possible for you to provide me with a code sample on how to
> convert a char* to little endian? I know it's probably a stupid question and
> I'm taking up your time, but I have to learn it somehow...
> Thanks in advance!
>
>
>
> Goblin_Queen wrote:
>
>> Thanks for your reply, I had thought of that too because my search lead me
>> to such an answer. How can I convert a char* from big endian to little
>> endian? I googled for conversion examples but I only found conversions for
>> int. I know this is probably a stupid question, but I'm still learning
>> C++.
>>
>>
>> Dr. Stephen Henson wrote:
>>
>>> On Wed, Mar 18, 2009, Goblin_Queen wrote:
>>>
>>>
>>>> Hello,
>>>>
>>>> I'm writing a program that has to sign a SHA1-hash value. I'm using
>>>> OpenSSL
>>>> to do this. My program has to do the same thing as another program which
>>>> makes use of Microsoft Crypto API. In that program the method
>>>> "CryptSignHash" was used in order to sign the hash value.
>>>>
>>>> When I try to sign a dummy hash value with RSA_sign, the result is
>>>> different
>>>> from the result I get from CryptSignHash. I've been searching for a
>>>> while to
>>>> find the reason for this, but haven't found the solution yet.
>>>>
>>>> I've also tried to sign the hash with other signature methods in
>>>> OpenSSL:
>>>> RSA_private_encrypt and EVP_SignFinal. Those gave me an error when I
>>>> tried
>>>> them, but I don't really know the difference between those 3 methods,
>>>> the
>>>> documentation isn't very clear, and I'm very new to cryptography
>>>> functions
>>>> and OpenSSL.
>>>>
>>>> Can anyone help me with this and tell me what I should use to get the
>>>> same
>>>> result as CryptSignHash returns?
>>>>
>>>> If you need to see my code in order to help me, just ask, then I'll post
>>>> it.
>>>>
>>> The output of CryptoAPI is in little endian format, OpenSSL and many
>>> others
>>> use big endian. Try reversing the bytes.
>>>
>>> Steve.
>>> --
>>> Dr Stephen N. Henson. Email, S/MIME and PGP keys: see homepage
>>> OpenSSL project core developer and freelance consultant.
>>> Homepage: http://www.drh-consultancy.demon.co.uk
>>> ______________________________________________________________________
>>> OpenSSL Project http://www.openssl.org
>>> User Support Mailing List openssl-users@openssl.org
>>> Automated List Manager majord...@openssl.org
>>>
>>>
>>>
>>
>>
>
>
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