(Delphi DLL) Extract PKCS7 Signature Digest

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

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, BinData, StringBuilder, Crypt2;

...

procedure TForm1.Button1Click(Sender: TObject);
var
crypt: HCkCrypt2;
p7mFile: PWideChar;
outPath: PWideChar;
verified: Boolean;
pkcs7Data: HCkBinData;
sbBase64: HCkStringBuilder;
hexStr: PWideChar;
bHaveBase64: Boolean;
i: Integer;
digest: PWideChar;

begin
// 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) then
  begin
    Memo1.Lines.Add(CkCrypt2__lastErrorText(crypt));
    Exit;
  end;

// How many signers?
// (The NumSignerCerts property is set whenever a signature is verified.)
Memo1.Lines.Add('Num Signers: ' + IntToStr(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) then
  begin
    bHaveBase64 := True;
    CkStringBuilder_Clear(sbBase64);
    CkStringBuilder_AppendBd(sbBase64,pkcs7Data,'utf-8',0,0);
  end;

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

while i < CkCrypt2_getNumSignerCerts(crypt) do
  begin
    if (bHaveBase64) then
      begin
        digest := CkCrypt2__pkcs7ExtractDigest(crypt,i,CkStringBuilder__getAsString(sbBase64));
      end
    else
      begin
        digest := CkCrypt2__pkcs7ExtractDigest(crypt,i,CkBinData__getEncoded(pkcs7Data,'base64'));
      end;
    if (CkCrypt2_getLastMethodSuccess(crypt) <> True) then
      begin
        Memo1.Lines.Add(CkCrypt2__lastErrorText(crypt));
        Exit;
      end;
    Memo1.Lines.Add('Signer ' + IntToStr(i + 1) + ' digest = ' + digest);
    i := i + 1;
  end;

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

end;