(MFC) Extract PKCS7 Signature Digest

Demonstrates how to extract a signature digest from a PKCS7 signature.

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

See Also: Using MFC CString in Chilkat

#include <CkCrypt2.h>
#include <CkBinData.h>
#include <CkStringBuilder.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // This example requires the Chilkat Crypt API to have been previously unlocked.
    // See Unlock Chilkat Crypt for sample code.

    CkCrypt2 crypt;

    const char *p7mFile = "qa_data/p7m/test.pdf.p7m";
    const char *outPath = "qa_output/test.pdf";

    // First let's see if this .p7m signature can be verified, and the original file extracted.
    bool verified = crypt.VerifyP7M(p7mFile,outPath);
    if (verified != true) {
        strOut.append(crypt.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // How many signers?
    // (The NumSignerCerts property is set whenever a signature is verified.)
    strOut.append("Num Signers: ");
    strOut.appendInt(crypt.get_NumSignerCerts());
    strOut.append("\r\n");

    // Load the .p7m into memory...
    CkBinData pkcs7Data;
    pkcs7Data.LoadFile(p7mFile);

    // Check to see if this .p7m contains the binary bytes, or if it's
    // already base64 encoded.  Get the 1st two bytes.  If the first two 
    // bytes are the us-ascii values "MI", then we have base64.
    CkStringBuilder sbBase64;
    const char *hexStr = pkcs7Data.getEncodedChunk(0,2,"hex");
    sbBase64.Append(hexStr);

    bool bHaveBase64 = false;
    if (sbBase64.ContentsEqual("4D49",true) == true) {
        bHaveBase64 = true;
        sbBase64.Clear();
        sbBase64.AppendBd(pkcs7Data,"utf-8",0,0);
    }

    // Get each signer's signature digest.
    crypt.put_EncodingMode("base64");
    int i = 0;
    const char *digest = 0;
    while (i < crypt.get_NumSignerCerts()) {
        if (bHaveBase64) {
            digest = crypt.pkcs7ExtractDigest(i,sbBase64.getAsString());
        }
        else {
            digest = crypt.pkcs7ExtractDigest(i,pkcs7Data.getEncoded("base64"));
        }

        if (crypt.get_LastMethodSuccess() != true) {
            strOut.append(crypt.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        strOut.append("Signer ");
        strOut.appendInt(i + 1);
        strOut.append(" digest = ");
        strOut.append(digest);
        strOut.append("\r\n");
        i = i + 1;
    }



    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }