XML Security Library

LibXML2
LibXSLT
OpenSSL

Creating dynamic templates.

The XML Security Library uses templates to describe how and what data should be signed or encrypted. The template is a regular XML file. You can create templates in advance using your favorite XML files editor, load them from a file and use for creating signature or encrypting data. You can also create templates dynamicaly. The XML Security Library provides helper functions to quickly create dynamic templates inside your application.


Creating dynamic signature templates.

The signature template has structure similar to the XML Digital Signature structure as it is described in specification. The only difference is that some nodes (for example, <dsig:DigestValue/> or <SignatureValue/>) are empty. The XML Security Library sets the content of these nodes after doing necessary calculations.

Figure 3. XML Digital Signature structure

<dsig:Signature ID?> 
    <dsig:SignedInfo>
        <dsig:CanonicalizationMethod Algorithm />
        <dsig:SignatureMethod Algorithm />
        (<dsig:Reference URI? >
    	    (<dsig:Transforms>
		(<dsig:Transform Algorithm />)+
	     </dsig:Transforms>)?
	    <dsig:DigestMethod Algorithm >
	    <dsig:DigestValue>
	</dsig:Reference>)+
    </dsig:SignedInfo>
    <dsig:SignatureValue> 
    (<dsig:KeyInfo>
	<dsig:KeyName>?
	<dsig:KeyValue>?
	<dsig:RetrievalMethod>?
	<dsig:X509Data>?
	<dsig:PGPData>?
	<enc:EncryptedKey>?
	<enc:AgreementMethod>?
	<dsig:KeyName>?
	<dsig:RetrievalMethod>?
	<*>?
    </dsig:KeyInfo>)?
    (<dsig:Object ID?>)*
</dsig:Signature>
	    

Example 7. Creating dynamic signature template.

/** 
 * sign_file:
 * @xml_file:		the XML file name.
 * @key_file:		the PEM private key file name.
 *
 * Signs the #xml_file using private key from #key_file and dynamicaly
 * created enveloped signature template.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
sign_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr signNode = NULL;
    xmlNodePtr refNode = NULL;
    xmlNodePtr keyInfoNode = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;
    
    assert(xml_file);
    assert(key_file);

    /* load doc file */
    doc = xmlParseFile(xml_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
	goto done;	
    }
    
    /* create signature template for RSA-SHA1 enveloped signature */
    signNode = xmlSecTmplSignatureCreate(doc, xmlSecTransformExclC14NId,
				         xmlSecTransformRsaSha1Id, NULL);
    if(signNode == NULL) {
	fprintf(stderr, "Error: failed to create signature template\n");
	goto done;		
    }

    /* add <dsig:Signature/> node to the doc */
    xmlAddChild(xmlDocGetRootElement(doc), signNode);
    
    /* add reference */
    refNode = xmlSecTmplSignatureAddReference(signNode, xmlSecTransformSha1Id,
					NULL, NULL, NULL);
    if(refNode == NULL) {
	fprintf(stderr, "Error: failed to add reference to signature template\n");
	goto done;		
    }

    /* add enveloped transform */
    if(xmlSecTmplReferenceAddTransform(refNode, xmlSecTransformEnvelopedId) == NULL) {
	fprintf(stderr, "Error: failed to add enveloped transform to reference\n");
	goto done;		
    }

    /* add <dsig:KeyInfo/> and <dsig:KeyName/> nodes to put key name in the signed document */
    keyInfoNode = xmlSecTmplSignatureEnsureKeyInfo(signNode, NULL);
    if(keyInfoNode == NULL) {
	fprintf(stderr, "Error: failed to add key info\n");
	goto done;		
    }

    if(xmlSecTmplKeyInfoAddKeyName(keyInfoNode, NULL) == NULL) {
	fprintf(stderr, "Error: failed to add key name\n");
	goto done;		
    }

    /* create signature context, we don't need keys manager in this example */
    dsigCtx = xmlSecDSigCtxCreate(NULL);
    if(dsigCtx == NULL) {
        fprintf(stderr,"Error: failed to create signature context\n");
	goto done;
    }

    /* load private key, assuming that there is not password */
    dsigCtx->signKey = xmlSecCryptoAppPemKeyLoad(key_file, NULL, NULL);
    if(dsigCtx->signKey == NULL) {
        fprintf(stderr,"Error: failed to load private pem key from \"%s\"\n", key_file);
	goto done;
    }

    /* set key name to the file name, this is just an example! */
    if(xmlSecKeySetName(dsigCtx->signKey, key_file) < 0) {
    	fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
	goto done;
    }

    /* sign the template */
    if(xmlSecDSigCtxSign(dsigCtx, signNode) < 0) {
        fprintf(stderr,"Error: signature failed\n");
	goto done;
    }
        
    /* print signed document to stdout */
    xmlDocDump(stdout, doc);
    
    /* success */
    res = 0;

done:    
    /* cleanup */
    if(dsigCtx != NULL) {
	xmlSecDSigCtxDestroy(dsigCtx);
    }
    
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}
		

Full program listing


Creating dynamic encryption templates.

The encryption template has structure similar to the XML Encryption structure as it is described in specification. The only difference is that some nodes (for example, <enc:CipherValue/>) are empty. The XML Security Library sets the content of these nodes after doing necessary calculations.

Figure 4. XML Encryption structure

<enc:EncryptedData Id? Type? MimeType? Encoding?>
    <enc:EncryptionMethod Algorithm />?
    (<dsig:KeyInfo>
	<dsig:KeyName>?
	<dsig:KeyValue>?
	<dsig:RetrievalMethod>?
	<dsig:X509Data>?
	<dsig:PGPData>?
	<enc:EncryptedKey>?
	<enc:AgreementMethod>?
	<dsig:KeyName>?
	<dsig:RetrievalMethod>?
	<*>?
    </dsig:KeyInfo>)?
    <enc:CipherData>
	<enc:CipherValue>?
	<enc:CipherReference URI?>?
    </enc:CipherData>
    <enc:EncryptionProperties>?
</enc:EncryptedData>	
	    

Example 8. Creating dynamic encrytion template.

/**
 * encrypt_file:
 * @xml_file:		the encryption template file name.
 * @key_file:		the Triple DES key file.
 *
 * Encrypts #xml_file using a dynamicaly created template and DES key from
 * #key_file.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
encrypt_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr encDataNode = NULL;
    xmlNodePtr keyInfoNode = NULL;
    xmlSecEncCtxPtr encCtx = NULL;
    int res = -1;
    
    assert(xml_file);
    assert(key_file);

    /* load template */
    doc = xmlParseFile(xml_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
	goto done;	
    }
    
    /* create encryption template to encrypt XML file and replace 
     * its content with encryption result */
    encDataNode = xmlSecTmplEncDataCreate(doc, xmlSecTransformDes3CbcId,
				NULL, xmlSecTypeEncElement, NULL, NULL);
    if(encDataNode == NULL) {
	fprintf(stderr, "Error: failed to create encryption template\n");
	goto done;   
    }

    /* we want to put encrypted data in the <enc:CipherValue/> node */
    if(xmlSecTmplEncDataEnsureCipherValue(encDataNode) == NULL) {
	fprintf(stderr, "Error: failed to add CipherValue node\n");
	goto done;   
    }

    /* add <dsig:KeyInfo/> and <dsig:KeyName/> nodes to put key name in the signed document */
    keyInfoNode = xmlSecTmplEncDataEnsureKeyInfo(encDataNode, NULL);
    if(keyInfoNode == NULL) {
	fprintf(stderr, "Error: failed to add key info\n");
	goto done;		
    }

    if(xmlSecTmplKeyInfoAddKeyName(keyInfoNode, NULL) == NULL) {
	fprintf(stderr, "Error: failed to add key name\n");
	goto done;		
    }

    /* create encryption context, we don't need keys manager in this example */
    encCtx = xmlSecEncCtxCreate(NULL);
    if(encCtx == NULL) {
        fprintf(stderr,"Error: failed to create encryption context\n");
	goto done;
    }

    /* load DES key, assuming that there is not password */
    encCtx->encKey = xmlSecKeyReadBinaryFile(xmlSecKeyDataDesId, key_file);
    if(encCtx->encKey == NULL) {
        fprintf(stderr,"Error: failed to load des key from binary file \"%s\"\n", key_file);
	goto done;
    }

    /* set key name to the file name, this is just an example! */
    if(xmlSecKeySetName(encCtx->encKey, key_file) < 0) {
    	fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
	goto done;
    }

    /* encrypt the data */
    if(xmlSecEncCtxXmlEncrypt(encCtx, encDataNode, xmlDocGetRootElement(doc)) < 0) {
        fprintf(stderr,"Error: encryption failed\n");
	goto done;
    }
    
    /* we template is inserted in the doc */
    encDataNode = NULL;
        
    /* print encrypted data with document to stdout */
    xmlDocDump(stdout, doc);
    
    /* success */
    res = 0;

done:    

    /* cleanup */
    if(encCtx != NULL) {
	xmlSecEncCtxDestroy(encCtx);
    }

    if(encDataNode != NULL) {
	xmlFreeNode(encDataNode);
    }
        
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}
		

Full program listing



Aleksey Sanin