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04.04.2008 at 03:14AM PDT, ID: 23295501

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8.1

Rewrite function to work with AnsiString

Zones: C++ Builder, C++ Programming Language

Tags: Borland C++ Builder 6

Hi,

Found a snippet which allows you to convert char* into a MD5 hash.

Since I am coding in Borland C++ with all its noobish objects like AnsiString.
And since I'm newbish at the rewriting-the-code-to-work-like-you-want-it thing I am asking for help here.

I need this function to return the hash in AnsiString format. Also the parameters of the function will only be AnsiString

For example:
AnsiString Str = "This is my string";
AnsiString Hash = MD5(Str);

         
           
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             #include <wincrypto.h>
 
bool md5(unsigned char hash[16], unsigned char *buf, int len)
{
    HCRYPTPROV hCryptProv;
    HCRYPTHASH hHash;
    BYTE bHash[0x7f];
    DWORD dwHashLen = 16;
    DWORD cbContent = len;
    BYTE* pbContent = (BYTE*)buf;
 
    if(CryptAcquireContext(&hCryptProv,
        NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET))
    {
 
        if(CryptCreateHash(hCryptProv,
            CALG_MD5,    
            0, 0, &hHash))
        {
            if(CryptHashData(hHash, pbContent, cbContent, 0))
            {
                if(CryptGetHashParam(hHash, HP_HASHVAL, bHash, &dwHashLen, 0))
                {
                    memcpy(hash, bHash, 16);
                }
                else return false;
            }
            else return false;
        }
        else return false;
    }
    else return false;
 
    CryptDestroyHash(hHash);
    CryptReleaseContext(hCryptProv, 0);
 
    return true;
}

           
         

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Question Stats

Zone: Programming

Question Asked By: Jammer1224

Solution Provided By: Kdo

Participating Experts: 1

Solution Grade: A

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04.04.2008 at 05:10AM PDT, ID: 21280779

Rank: Master

Kdo:

Hi Jammer1224,

It will probably make the most sense if you change the actual code as little as possible. That's pretty easy to accommodate by changing the header and moving necessary items to stack variables.

I've not tested it, but something like I've attached below should be a good start.

C++ Builder handles conventional strings just fine (char Array[]). Why do you need to return an AnsiString?

Good Luck,
Kent

                       
         
           
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             AnsiString md5 (AnsiString Source)
{ 
  HCRYPTPROV hCryptProv;
  HCRYPTHASH hHash;
  BYTE bHash[0x7f];
  DWORD dwHashLen = 16;
  DWORD cbContent = len;
  BYTE* pbContent = (BYTE*)buf;  
//  New variables -- originally on the function's parameter list 
  unsigned char hash [16+1];// The buffer where the md5 hash will be built
  unsigned char *buf;       // Originally this was the buffer to hash
  int      len;             // Original buffer length; 
  len = Source.Length ();
  buf = (unsigned char*)Source.c_ptr (); 
  if (CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET))
  {
    if (CryptCreateHash (hCryptProv, CALG_MD5, 0, 0, &hHash))
    {
      if (CryptHashData (hHash, pbContent, cbContent, 0))
      {
        if (CryptGetHashParam (hHash, HP_HASHVAL, bHash, &dwHashLen, 0))
        {
          memcpy(hash, bHash, 16);
        }
        else return "";
      }
      else return "";
    }
    else return "";
  }
  else return "";
 
  CryptDestroyHash(hHash);
  CryptReleaseContext(hCryptProv, 0);
 
  hash[16] = 0;   // Append a stringterminator to the hash 
  return (AnsiString) (hash);
}

           
         

Open in New Window

04.04.2008 at 05:28AM PDT, ID: 21280896

Jammer1224:

Because I'm not good at converting variables from one type to another.
It took me 2 days to figure out how to convert a number stored in a string to a int :)
First of all, to correct something that you did wrong, old variables must be declared below the new ones.
Also the typing mistake you made:
buf = (unsigned char*)Source.c_ptr ();
It should be:
buf = (unsigned char*)Source.c_str ();

Stating these mistakes in case if someone more novice then me looks for solution like this.

Secondly, I get a compiler error:
[C++ Error] Unit1.cpp(208): E2285 Could not find a match for 'AnsiString::AnsiString(unsigned char *)'
[C++ Error] Unit1.cpp(208): E2031 Cannot cast from 'unsigned char *' to 'AnsiString'

@ return (AnsiString) (hash);

04.04.2008 at 05:35AM PDT, ID: 21280957

Rank: Master

Kdo:

Hi Jammer1224,

c_ptr / c_str ... I've been using C++Builder since it first came out and I still do that in my own code about 1/2 the time. :)

The error must be on the last line. We'll just recast twice.

return (AnsiString)(char *)(hash);

Note that you can also call the original function, and preform just this double recast on the returned buffer hash[]. Though you'll have to take the same caution to ensure that it is null terminated.

Good Luck,
Kent

04.04.2008 at 06:00AM PDT, ID: 21281155

Jammer1224:

It returns me an:

[C++ Error] Unit1.cpp(183): E2316 'c_ptr' is not a member of 'AnsiString'

when using ptr

When I use c_str the hash looks awfull.
the bHash looks even worse... (see picture attached)

Maby thats because I use c_str not c_ptr?

If not, maby you see the problem of this snippet?
I really need to add MD5 somehow to the code I am writing.

I do not know how to use DLL's (but I have one which has a MD5 convertion function in it).

Also I have got some cc files which could be used to add a MD5 function to the, but again, I have no knowledge how to use them.

The cc files can be found:
http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html
Or direct: http://userpages.umbc.edu/~mabzug1/cs/md5/md5-cc-102.tar.gz

TheHorror.JPG (79 KB) (File Type Details)

Values of the hashes.

04.04.2008 at 06:20AM PDT, ID: 21281339

Rank: Master

Kdo:

Hi Jammer1224,

An md5 hash is really a 16*8 bit (128) bit value. You can not directly display the AnsiString value where you've put it. Instead, you'll need to convert each 4-bit value to hex, just as if it were in a char[16].

I think that you'll be better off if we start back at the ground level and rework this. An md5 value in an AnsiString may be "portable", but it's not much good for anything else.

A lightweight wrapper class around the md5 algorithm(s) might be the right way to go.

Good Luck,
Kent

                       
         
           
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             class mymd5
{
  public:
    bool md5 (AnsiString);
    char DisplayValue [17]; 
  private:
    unsigned char hash[16];
    bool     Success;
}; 
bool mymd5::md5 (AnsiString Source)
{
  Success = md5 (hash, (unsigned char*)Source.c_str (), Source.Length);
  if (Success)
  {
    for (int idx = 0; unsigned char *ptr = hash; ++idx, ++ptr)
    {
      DisplayValue[idx*2] = (char*)"0123456789ABCDEF"[(*ptr)>>4];
      DisplayValue[idx*2+1] = (char*)"0123456789ABCDEF"[(*ptr)& 0xF)];
    }
    DisplayValue[16] = 0;
  }
  else
    DispalyValue[0] = 0;
  return Success;
}
           
         

Open in New Window

Accepted Solution

04.04.2008 at 07:37AM PDT, ID: 21282186

Jammer1224:

There must be a mistake somewhere in :
for (int idx = 0; unsigned char *ptr = hash; ++idx, ++ptr)
{
DisplayValue[idx*2] = (char *)"0123456789ABCDEF"[(*ptr)>>4];
DisplayValue[idx*2+1] = (char *)"0123456789ABCDEF"[(*ptr)&0xF];
}

I guess we need to use (char).
If using char i get an access error when building without debug.

When debugging seems that the DisplayValue gets A2A2A2.....A2A2A2A2.....
and the hash value gets:
hash = hash + DisplayValue...
Also the loop seems to be infinite.

04.04.2008 at 10:20AM PDT, ID: 21283791

Rank: Master

Kdo:

Hi Jammer1224,

Ok. I'd used that before so I guess that I mistyped something.

Create an array with the hex digits.

static const char HexDigit[16] = "0123456789ABCDEF";

Then reference it

for (int idx = 0; unsigned char *ptr = hash; ++idx, ++ptr)
{
DisplayValue[idx*2] = HexDigit [(*ptr)>>4];
DisplayValue[idx*2+1] = HexDigit [(*ptr)&0xF];
}

Good Luck,
Kent

04.04.2008 at 01:58PM PDT, ID: 21285606

Jammer1224:

No still does not work.
Still an access point error.
I'm using it this way because I do not know how to use classes.
Both functions declared in the Form class.

                       
         
           
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             String TForm1::MD5(AnsiString Source)
{
        unsigned char hash[16];
        bool     Success;
        char DisplayValue [17];
  Success = MD5Hex(hash, (unsigned char*)Source.c_str (), Source.Length());
  if (Success)
  {
  static const char HexDigit[16] = "0123456789ABCDEF";
      for (int idx = 0; unsigned char *ptr = hash; ++idx, ++ptr)
      {
        DisplayValue[idx*2] = HexDigit [(*ptr)>>4];
        DisplayValue[idx*2+1] = HexDigit [(*ptr)&0xF];
      }
 
    DisplayValue[16] = 0;
    return (String)DisplayValue;
  }
  return "";
}
bool TForm1::MD5Hex(unsigned char hash[16], unsigned char *buf, int len)
{
    HCRYPTPROV hCryptProv;
    HCRYPTHASH hHash;
    BYTE bHash[0x7f];
    DWORD dwHashLen = 16;
    DWORD cbContent = len;
    BYTE* pbContent = (BYTE*)buf;
 
    if(CryptAcquireContext(&hCryptProv,
        NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET))
    {
 
        if(CryptCreateHash(hCryptProv,
            CALG_MD5,    //  wincrypt.h
            0, 0, &hHash))
        {
            if(CryptHashData(hHash, pbContent, cbContent, 0))
            {
                if(CryptGetHashParam(hHash, HP_HASHVAL, bHash, &dwHashLen, 0))
                {
                    memcpy(hash, bHash, 16);
                }
                else return false;
            }
            else return false;
        }
        else return false;
    }
    else return false;
 
    CryptDestroyHash(hHash);
    CryptReleaseContext(hCryptProv, 0);
    return true;
}
           
         

Open in New Window

04.05.2008 at 06:50PM PDT, ID: 21290370

Jammer1224:

Edited your code a bit and it works. Thanks.

20080236-EE-VQP-29 / EE_QW_2_20070628