Thanks Guy,

i did the following commands in OPENSSL for genearation certificate and private key

private key and CSR(certificate signing request)

req -new -newkey rsa:2048 -nodes -keyout localhost.key -out localhost.csr

For Self Signed Certificate:

x509 -req -days 365 -in localhost.csr -signkey localhost.key -out localhost.crt

pkcs8 decrypted private key 

pkcs8 -topk8 -nocrypt -in localhost.key  -out pkcs8.pem

below is the code :

public class serviceClient{

public static String generateXMLSignature(String docBodyString){
// 1. Apply the Transforms, as determined by the application, to the data object.
// (no transforms are done, since the body should be delivered in canonicalized form (Force.com offers no canonicalization algorithm))

// 2. Calculate the digest value over the resulting data object.
//String dBS= docBodyString;


Blob bodyDigest = Crypto.generateDigest('SHA1',Blob.valueOf(docBodyString));
system.debug('Testing*****'+bodyDigest);
// 3. Create a Reference element, including the (optional) identification of the data object, any (optional) transform elements, the digest algorithm and the DigestValue.
// (Note, it is the canonical form of these references that are signed and validated in next steps.)

String referenceString = '';
referenceString += '';
referenceString += '<ds:Reference URI="#id-1367626116">';
referenceString += '<ds:Transforms>';
//referenceString += '<ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"></ds:Transform>';
referenceString += '<ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"></ds:Transform>';
referenceString += '</ds:Transforms>';
referenceString += '<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"></ds:DigestMethod>';
referenceString += '<ds:DigestValue>'+EncodingUtil.base64Encode(bodyDigest)+'</ds:DigestValue>';
referenceString += '</ds:Reference>';

// 4. Create SignedInfo element with SignatureMethod, CanonicalizationMethod and Reference(s).
String signedInfoString = '';
signedInfoString += '<ds:SignedInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">';
signedInfoString += '<ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"></ds:CanonicalizationMethod>';
signedInfoString += '<ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"></ds:SignatureMethod>';
signedInfoString += referenceString;
signedInfoString += '</ds:SignedInfo>';

// 5. Canonicalize and then calculate the SignatureValue over SignedInfo based on algorithms specified in SignedInfo.
// (no canonicalization is done, since the signedinfo element should be delivered in canonicalized form (Force.com offers no canonicalization algorithm))

String algorithmName = 'RSA-SHA1';
// decrypted private key pkcs8 format from certificate
String key = 'PKCS8 DECRPTED PRIVATE KEY';

Blob privateKey = EncodingUtil.base64Decode(key);

Blob siBlob = Blob.valueOf(signedInfoString);

Blob signatureValue = Crypto.sign(algorithmName, siBlob, privateKey);
String signatureValueString = EncodingUtil.base64Encode(signatureValue);
//String signatureValueString = EncodingUtil.base64Encode(privateKey);
// 6. Construct the Signature element that includes SignedInfo, Object(s) (if desired, encoding may be different than that used for signing), KeyInfo (if required), and SignatureValue.
String signatureString = '';
signatureString += '<wsse:Security soapenv:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd">';
signatureString += '<wsse:BinarySecurityToken EncodingType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary" ValueType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3" wsu:Id="CertId-1828792" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">CERTIFICATE</wsse:BinarySecurityToken>';
signatureString += '<ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">';
signatureString += signedInfoString;
signatureString += '<ds:SignatureValue xmlns:ds="http://www.w3.org/2000/09/xmldsig#">'+signatureValueString+'</ds:SignatureValue>';
signatureString += '<ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">';
signatureString += '<wsse:SecurityTokenReference wsu:Id="STRId-308417122" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"><wsse:Reference URI="#CertId-1828792" ValueType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3"/></wsse:SecurityTokenReference>';
//signatureString += '</ds:X509Data>';
signatureString += '</ds:KeyInfo>';
signatureString += '</ds:Signature>';
signatureString += '</wsse:Security>';
return signatureString;
}
public static void doModelCallout() {

String url = 'https://ws-stga.bcbsfl.com:443/cip/1.0/FloridaBlueMemberEmailUpdate';
Http h = new Http();
HttpRequest req = new HttpRequest();
req.setEndpoint(url);
req.setMethod('POST');
req.setHeader('Content-Type','application/soap+xml');
req.setHeader('SOAPAction', url);

String ApplicationId = '270';
String TransactionId='1231323131';
Date TransactionDate= System.Today();
//String
String docOpenEnvString = '';
String docOpenHeaderString = '';
String docClosingHeaderString = '';
String docOpenBodyString = '';
String docSignatureString = '';
String docClosingBodyString = '';
String docClosingEnvString = '';
String soapNS = 'http://schemas.xmlsoap.org/soap/envelope/';
String xsi = 'http://www.w3.org/2001/XMLSchema-instance';
String serviceNS = 'http://essent.nl/sco_generic_b2b/services';

// add xml tag
docOpenEnvString += '<?xml version="1.0" encoding="UTF-8"?>';
// open envelope
docOpenEnvString += '<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mem="http://MemberUpdater.crm.floridablue.com" xsi:schemaLocation="http://schemas.xmlsoap.org/soap/envelope/ http://schemas.xmlsoap.org/soap/envelope/">';
// put header (as long as msg is not signed)
docOpenHeaderString += '<soapenv:Header>';
docClosingHeaderString += '</soapenv:Header>';

// open Body and Service

// open Request
docOpenBodyString += '<soapenv:Body wsu:Id="id-1367626116" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">..............</soapenv:Body>';

// close Request
// docClosingBodyString += '</request>';
// close Body and Service
// docClosingBodyString += '</ns0:EndUserDealService></soapenv:Body>';
// close envelope
docClosingEnvString += '</soapenv:Envelope>';

String docBodyString = docOpenBodyString + docClosingBodyString;

// 2. ADD SIGNATURE
docSignatureString = generateXMLSignature(docBodyString);
String docString = docOpenEnvString + docOpenHeaderString + docSignatureString + docClosingHeaderString + docBodyString + docClosingEnvString;

req.setBody(docString);

HttpResponse res = h.send(req);
System.Debug(res);

}

}

I am doing anything wrong in this, please let me know thanks.