(MFC) Hash a Hex String

Demonstrates common pitfalls in hashing a hex string..

Note: This example requires Chilkat v9.5.0.70 or greater.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkCrypt2.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkCrypt2 crypt;

    // We have a hex string to be SHA-256 hashed:  "b08538d832bf"
    // The result we expect to receive is "8a9f04cb1adfbd7f59c5918635f92f6c847e5b15f9828519d2fdbd6ead0918fc"

    const char *strToHash = "b08538d832bf";

    // How do we get this result?

    // The 1st question to be answered is:  What bytes are getting hashed?  
    // There are two possibilities:
    // 1) Hash 12 bytes, namely the us-ascii values for 'b', '0', '8', '5', .... 'b', 'f'
    // or
    // 2) Hash 6 bytes:  0xb0, 0x85, ... 0xbf
    // 

    // This is how to hash the 12 us-ascii byte values:
    // The Charset property defines the byte representation of the string passed to the hash algorithm:
    crypt.put_Charset("us-ascii");
    // The EncodingMode property defines the binary encoding (hex, base64, etc.) of the hash returned as an encoded string.
    crypt.put_EncodingMode("hex");
    crypt.put_HashAlgorithm("sha256");

    const char *hashValue = crypt.hashStringENC(strToHash);
    strOut.append(crypt.lastErrorText());
    strOut.append("\r\n");
    strOut.append("hash of 12 us-ascii bytes: ");
    strOut.append(hashValue);
    strOut.append("\r\n");

    // The result is:  327F2B33A0F0580D09840B0D7CEE54514CA33E9A  (not what we were hoping).

    // -------------------------------------------
    // This is how to hash the 6 bytes
    // 
    // "hex" is not an actual character encoding.  It's a special value to be used to tell Chilkat to hex decode
    // the string and pass the decoded bytes to the hash algorithm...
    // Note: This example requires Chilkat v9.5.0.70 or greater for the "hex" Charset to work properly.
    crypt.put_Charset("hex");
    // The EncodingMode and HashAlgorithm remain the same..
    hashValue = crypt.hashStringENC(strToHash);
    strOut.append(crypt.lastErrorText());
    strOut.append("\r\n");
    strOut.append("hash of 6 hex bytes: ");
    strOut.append(hashValue);
    strOut.append("\r\n");

    // The result is 8A9F04CB1ADFBD7F59C5918635F92F6C847E5B15F9828519D2FDBD6EAD0918FC (which equals the hash we were expecting)


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }