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Digital Signatures

, 11 Sep 2008 CPOL
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Custom digital signatures using iTextSharp

itextsharp

Introduction

In this article, I will present a simple source code allowing you to digitally sign a PDF document and modify its meta data. I will use the excellent and free port of the iText library: iTextSharp, that can be downloaded here. You'll need Visual Studio 2008 to be able to open and build the project.

If you don’t know what digital signatures are or how they work, you can go here or here, or simply ask Google Smile | :) .

iTextSharp provides a lot of interesting features to create and manipulate PDF documents, but in this article, we will only use the digital signature functions. I will also use some functions to manipulate PKCS#12 certificates. The only thing you need to know here is that our digital signature will use a private key extracted from a PKCS#12 certificate.

Background

I prefer e-signing of an iTextSharp document first, and then doing any change/modification as per requirements.

Using the code

string signerName = 
       PdfPKCS7.GetSubjectFields(this.myCert.Chain[0]).GetField("CN");
PdfTemplate template = st.SignatureAppearance.GetLayer(2);
template.MoveTo(0, 200);
template.LineTo(500, 0);
template.Stroke();
template.BeginText();
BaseFont bf1 = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, 
                                   BaseFont.NOT_EMBEDDED);
template.SetFontAndSize(bf1, 10);
template.SetTextMatrix(1, 1);
template.ShowTextAligned(PdfContentByte.ALIGN_LEFT, "" + 
                         signerName + "", 0, 40, 0);

BaseFont bf = BaseFont.CreateFont(BaseFont.HELVETICA, 
              BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
template.SetFontAndSize(bf, 7);
template.SetTextMatrix(1, 1);
template.ShowTextAligned(PdfContentByte.ALIGN_LEFT, "" + 
         System.DateTime.Now.ToString("yyyy.MM.dd HH:mm:ss zzz") + "", 
         50, 30, 0);

template.SetFontAndSize(bf, 7);
template.SetTextMatrix(1, 1);
template.ShowTextAligned(PdfContentByte.ALIGN_LEFT, "Signer:", 0, 25, 0);

template.SetFontAndSize(bf, 7);
template.SetTextMatrix(1, 1);
template.ShowTextAligned(PdfContentByte.ALIGN_LEFT, "" + "CN=" + 
         PdfPKCS7.GetSubjectFields(myCert.Chain[0]).GetField("CN") + "", 
         10, 17, 0);



template.SetFontAndSize(bf, 7);
template.SetTextMatrix(1, 1);
template.ShowTextAligned(PdfContentByte.ALIGN_LEFT, "" + "C=" + 
                         PdfPKCS7.GetSubjectFields(myCert.Chain[0]).GetField("C") + "", 
                         10, 10, 0);

template.EndText();

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

nimeshmca
Software Developer (Senior) Business Solution
India India
i m Software Developer

Comments and Discussions

 
QuestionSet revision label and Add picture as signature PinmemberRui Frazao26-Feb-14 1:22 
Questionmeta tags PinmemberKalpana Volety12-Jan-13 3:43 
Generalhelp!!! PinmemberROHIT KUMAR GAUTAM13-Jul-11 0:38 
General.CER instead of .PFX certificates PinmemberMiroslav Karaffa9-May-11 3:48 
GeneralADD IMAGE And languages Pinmembershin99926-Dec-10 14:05 
Questionwork with asp.net? Pinmemberdavidberlin14-May-10 3:58 
Questionit is not working PinmemberDaulat Kadam2-Sep-09 2:59 
AnswerRe: it is not working Pinmembernimeshmca15-Feb-10 3:29 
AnswerRe: it is not working Pinmembernimeshmca15-Feb-10 3:29 
its working download again Laugh | :laugh:
QuestionHow will it works? PinmemberDaulat Kadam2-Sep-09 2:18 
GeneralLocation of the signaure Pinmemberju168181-Jul-09 17:41 
GeneralRe: Location of the signaure Pinmembernimeshmca15-Feb-10 3:30 
Generalgetting fields..... PinmemberJ .R. Martins4-May-09 6:21 
Questionhow to sign with Datetime sign (TSA server) ? PinmemberRani10928-Oct-08 13:09 
AnswerRe: how to sign with Datetime sign (TSA server) ? Pinmembernimeshmca16-Mar-09 23:09 

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