(C) Extract PKCS7 Signature Digest

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

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#include <C_CkCrypt2.h>
#include <C_CkBinData.h>
#include <C_CkStringBuilder.h>

void ChilkatSample(void)
    {
    HCkCrypt2 crypt;
    const char *p7mFile;
    const char *outPath;
    BOOL verified;
    HCkBinData pkcs7Data;
    HCkStringBuilder sbBase64;
    const char *hexStr;
    BOOL bHaveBase64;
    int i;
    const char *digest;

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

    crypt = CkCrypt2_Create();

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

    // First let's see if this .p7m signature can be verified, and the original file extracted.
    verified = CkCrypt2_VerifyP7M(crypt,p7mFile,outPath);
    if (verified != TRUE) {
        printf("%s\n",CkCrypt2_lastErrorText(crypt));
        CkCrypt2_Dispose(crypt);
        return;
    }

    // How many signers?
    // (The NumSignerCerts property is set whenever a signature is verified.)
    printf("Num Signers: %d\n",CkCrypt2_getNumSignerCerts(crypt));

    // Load the .p7m into memory...
    pkcs7Data = CkBinData_Create();
    CkBinData_LoadFile(pkcs7Data,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.
    sbBase64 = CkStringBuilder_Create();
    hexStr = CkBinData_getEncodedChunk(pkcs7Data,0,2,"hex");
    CkStringBuilder_Append(sbBase64,hexStr);

    bHaveBase64 = FALSE;
    if (CkStringBuilder_ContentsEqual(sbBase64,"4D49",TRUE) == TRUE) {
        bHaveBase64 = TRUE;
        CkStringBuilder_Clear(sbBase64);
        CkStringBuilder_AppendBd(sbBase64,pkcs7Data,"utf-8",0,0);
    }

    // Get each signer's signature digest.
    CkCrypt2_putEncodingMode(crypt,"base64");
    i = 0;

    while (i < CkCrypt2_getNumSignerCerts(crypt)) {
        if (bHaveBase64) {
            digest = CkCrypt2_pkcs7ExtractDigest(crypt,i,CkStringBuilder_getAsString(sbBase64));
        }
        else {
            digest = CkCrypt2_pkcs7ExtractDigest(crypt,i,CkBinData_getEncoded(pkcs7Data,"base64"));
        }

        if (CkCrypt2_getLastMethodSuccess(crypt) != TRUE) {
            printf("%s\n",CkCrypt2_lastErrorText(crypt));
            CkCrypt2_Dispose(crypt);
            CkBinData_Dispose(pkcs7Data);
            CkStringBuilder_Dispose(sbBase64);
            return;
        }

        printf("Signer %d digest = %s\n",i + 1,digest);
        i = i + 1;
    }



    CkCrypt2_Dispose(crypt);
    CkBinData_Dispose(pkcs7Data);
    CkStringBuilder_Dispose(sbBase64);

    }