How to obtain signer’s details from a JavaScript signed data

In a previous post I described how to sign data with only javascript. Now, this data should be used on the server side for something. Here is how a Java developer can extract the signature details, and verify whether the content received from a form is really what has been signed. The general scenario is – a user submits a form, the data from which he signs. Then on the server the submitted data should be verified against the signed (PKCS7) data.

One needs the Bouncycastle libraries and apache commons codec:

package com.materna.remedy.plugins;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;

import org.apache.commons.codec.binary.Base64;
import org.bouncycastle.cms.CMSProcessable;
import org.bouncycastle.cms.CMSProcessableByteArray;
import org.bouncycastle.cms.CMSSignedData;
import org.bouncycastle.cms.SignerInformation;
import org.bouncycastle.cms.SignerInformationStore;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class CertificateDataExctractor {
	private Map<String, Object> extractInfos(String base64EncodedPKCS7,
			String contentString, boolean isIe) {
		try {
			byte[] data = Base64.decodeBase64(base64EncodedPKCS7.trim().getBytes());

			Security.addProvider(new BouncyCastleProvider());

			CMSSignedData signedData = new CMSSignedData(data);

			if (signedData.getSignedContent() == null) {
				byte[] contentBytes;
				if (!isIe) {
					contentBytes = contentString.getBytes();
				} else {
					contentBytes = contentString.getBytes("UnicodeLittleUnmarked");

				CMSProcessable cmsProcesableContent = new CMSProcessableByteArray(
				signedData = new CMSSignedData(cmsProcesableContent, data);

			CertStore certsStore = signedData.getCertificatesAndCRLs(
					"Collection", "BC");
			SignerInformationStore signersStores = signedData.getSignerInfos();

			boolean verified = true;
			boolean validCertificate = true;
			Map<String, Object> signerData = null;

			for (Iterator<SignerInformation> iter = signersStores.getSigners()
					.iterator(); iter.hasNext();) {
				SignerInformation signer =;
				// emulate(signer);

				Collection certCollection = certsStore.getCertificates(signer

				if (!certCollection.isEmpty()) {
					X509Certificate cert = (X509Certificate) certCollection

					try {
						if (!signer.verify(cert.getPublicKey(), "BC")) {
							verified = false;
					} catch (Exception ex) {
						// if this is an attempt to verify it assuming Firefox,
						// try assuming IE. If it is already IE - the
						// verification doesn't pass
						if (!isIe) {
							return extractInfos(base64EncodedPKCS7,
									contentString, true);
						verified = false;

					// If this is the last signer in the chain, obtain the data
					if (!iter.hasNext()) {
						signerData = extractSubjectInfos(cert);
			return signerData;
		} catch (Exception ex) {
			return null;


And of course, you provide your own implementation of getSubjectInfos method, putting whatever data you need from the certificate in the Map.


14 Responses to “How to obtain signer’s details from a JavaScript signed data”

  1. 使用CAPICOM实现证书管理 « 出家如初,成佛有余 Says:

    […] How to obtain signer’s details from a JavaScript signed data […]

  2. Sujita Says:

    I used crypto.signText to get signed data and then pass that signed data to above mehtod i got following error

    org.bouncycastle.cms.CMSException: message-digest attribute value does not match calculated value
    at org.bouncycastle.cms.SignerInformation.doVerify(Unknown Source)
    at org.bouncycastle.cms.SignerInformation.verify(Unknown Source)
    at org.bouncycastle.cms.SignerInformation.verify(Unknown Source)
    at test.CertificateDataExctractor.extractInfos(
    at test.CertificateDataExctractor.main(

    can u tell me what i am doing wrong

  3. Ashish Says:

    I am signing with capicom activex and java script at client end.At server end,i need to convert that signature into pkcs7 compatible format.Can anybody give me any suggestions..

  4. Ashish Says:

    can you give .net compatible code to do this??

  5. My Blog » 使用CAPICOM实现证书管理 Says:

    […] How to obtain signer’s details from a JavaScript signed data […]

  6. Nikolai Kosev Says:

    1. Principal p = cert.getSubjectDN();

    2. String tmpSDN = p.getName();
    On row 2 you can get the SubjectDN from the signer’s certificate where you have all the data about the signer( Name, email, etc.)

    3. int beg = tmpSDN.indexOf(“CN=”);
    4. //int end = tmpSDN.indexOf(“,E=”);
    5. int end = tmpSDN.indexOf(“,L=”);
    6. String signerName = tmpSDN.substring(beg+3, end);
    On row 6 you get the name of the person wich the certificate belong to

  7. sena redyy Says:

    Can i get publickey information through javascript… please i am new to this

    thank you

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    Way cool! Some very valid points! I appreciate you writing this write-up and the
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  13. MadhavN Says:


    signer.verify(cert.getPublicKey(), “BC”),

    the above line always fails. i am not able to debug where exactly is an issue. So can guide me what the signer object contains and how the verification is happening with public key. thanks in advance

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