## Signing a node by ID with X509 certificate.

### sign4.c

    /**
     * XML Security Library example: Signing a file with a dynamicaly created template and an X509 certificate.
     *
     * Signs a file using a dynamicaly created template, key from PEM file and
     * an X509 certificate. The signature has one reference using "ID" attribute
     * of the node to be signed. The key certificate is written in the <dsig:X509Data/> node.
     *
     * This example was developed and tested with OpenSSL crypto library. The
     * certificates management policies for another crypto library may break it.
     *
     * Usage:
     *      sign4 <xml-doc> <id-attribute-to-sign> <pem-key-file> <pem-cert-file>
     *
     * Example:
     *      ./sign4 sign4-doc.xml "data" rsakey.pem rsacert.pem > sign4-res.xml
     *
     * The result signature could be validated using verify3 example:
     *      ./verify3 sign4-res.xml ca2cert.pem cacert.pem
     *
     * This is free software; see Copyright file in the source
     * distribution for preciese wording.
     *
     * Copyright (C) 2002-2024 Aleksey Sanin <aleksey@aleksey.com>. All Rights Reserved.
     */
    #include <stdlib.h>
    #include <string.h>
    #include <assert.h>

    #include <libxml/tree.h>
    #include <libxml/xmlmemory.h>
    #include <libxml/parser.h>

    #ifndef XMLSEC_NO_XSLT
    #include <libxslt/xslt.h>
    #include <libxslt/security.h>
    #endif /* XMLSEC_NO_XSLT */

    #include <xmlsec/xmlsec.h>
    #include <xmlsec/xmltree.h>
    #include <xmlsec/xmldsig.h>
    #include <xmlsec/templates.h>
    #include <xmlsec/crypto.h>

    int sign_file(const char* xml_file, const char* id_attr, const char* key_file, const char* cert_file);

    int
    main(int argc, char **argv) {
    #ifndef XMLSEC_NO_XSLT
        xsltSecurityPrefsPtr xsltSecPrefs = NULL;
    #endif /* XMLSEC_NO_XSLT */

        assert(argv);

        if(argc != 5) {
            fprintf(stderr, "Error: wrong number of arguments.\n");
            fprintf(stderr, "Usage: %s <xml-file> <id-attr> <key-file> <cert-file>\n", argv[0]);
            return(1);
        }

        /* Init libxml and libxslt libraries */
        xmlInitParser();
        LIBXML_TEST_VERSION
        xmlLoadExtDtdDefaultValue = XML_DETECT_IDS | XML_COMPLETE_ATTRS;
        xmlSubstituteEntitiesDefault(1);

        /* Init libxslt */
    #ifndef XMLSEC_NO_XSLT
        /* disable everything */
        xsltSecPrefs = xsltNewSecurityPrefs();
        xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_READ_FILE,        xsltSecurityForbid);
        xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_WRITE_FILE,       xsltSecurityForbid);
        xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_CREATE_DIRECTORY, xsltSecurityForbid);
        xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_READ_NETWORK,     xsltSecurityForbid);
        xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_WRITE_NETWORK,    xsltSecurityForbid);
        xsltSetDefaultSecurityPrefs(xsltSecPrefs);
    #endif /* XMLSEC_NO_XSLT */

        /* Init xmlsec library */
        if(xmlSecInit() < 0) {
            fprintf(stderr, "Error: xmlsec initialization failed.\n");
            return(-1);
        }

        /* Check loaded library version */
        if(xmlSecCheckVersion() != 1) {
            fprintf(stderr, "Error: loaded xmlsec library version is not compatible.\n");
            return(-1);
        }

        /* Load default crypto engine if we are supporting dynamic
         * loading for xmlsec-crypto libraries. Use the crypto library
         * name ("openssl", "nss", etc.) to load corresponding
         * xmlsec-crypto library.
         */
    #ifdef XMLSEC_CRYPTO_DYNAMIC_LOADING
        if(xmlSecCryptoDLLoadLibrary(NULL) < 0) {
            fprintf(stderr, "Error: unable to load default xmlsec-crypto library. Make sure\n"
                            "that you have it installed and check shared libraries path\n"
                            "(LD_LIBRARY_PATH and/or LTDL_LIBRARY_PATH) environment variables.\n");
            return(-1);
        }
    #endif /* XMLSEC_CRYPTO_DYNAMIC_LOADING */

        /* Init crypto library */
        if(xmlSecCryptoAppInit(NULL) < 0) {
            fprintf(stderr, "Error: crypto initialization failed.\n");
            return(-1);
        }

        /* Init xmlsec-crypto library */
        if(xmlSecCryptoInit() < 0) {
            fprintf(stderr, "Error: xmlsec-crypto initialization failed.\n");
            return(-1);
        }

        if(sign_file(argv[1], argv[2], argv[3], argv[4]) < 0) {
            return(-1);
        }

        /* Shutdown xmlsec-crypto library */
        xmlSecCryptoShutdown();

        /* Shutdown crypto library */
        xmlSecCryptoAppShutdown();

        /* Shutdown xmlsec library */
        xmlSecShutdown();

        /* Shutdown libxslt/libxml */
    #ifndef XMLSEC_NO_XSLT
        xsltFreeSecurityPrefs(xsltSecPrefs);
        xsltCleanupGlobals();
    #endif /* XMLSEC_NO_XSLT */
        xmlCleanupParser();

        return(0);
    }

    /**
     * sign_file:
     * @xml_file:           the XML file name.
     * @id_attr:            the ID attribute of the node to sign.
     * @key_file:           the PEM private key file name.
     * @cert_file:          the x509 certificate PEM file.
     *
     * Signs the @xml_file using private key from @key_file and dynamicaly
     * created enveloped signature template. The certificate from @cert_file
     * is placed in the <dsig:X509Data/> node.
     *
     * Returns 0 on success or a negative value if an error occurs.
     */
    int
    sign_file(const char* xml_file, const char* id_attr, const char* key_file, const char* cert_file) {
        xmlDocPtr doc = NULL;
        xmlNodePtr signNode = NULL;
        xmlNodePtr refNode = NULL;
        xmlNodePtr keyInfoNode = NULL;
        xmlNodePtr x509DataNode = NULL;
        xmlSecDSigCtxPtr dsigCtx = NULL;
        char uri[1024];
        const xmlChar* id_attributes[] = { BAD_CAST "id", BAD_CAST "ID", NULL };
        int res = -1;

        assert(xml_file);
        assert(id_attr);
        assert(key_file);
        assert(cert_file);

        /* load doc file */
        doc = xmlReadFile(xml_file, NULL, XML_PARSE_PEDANTIC | XML_PARSE_NONET);
        if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
            fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
            goto done;
        }

        /* create signature template for RSA-SHA256 signature */
        signNode = xmlSecTmplSignatureCreate(doc, xmlSecTransformExclC14NId, xmlSecTransformRsaSha256Id, 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 */
        if (strlen(id_attr) + 2 > sizeof(uri)) {
            fprintf(stderr, "Error: id attribute is too long\n");
            goto done;
        }
        sprintf(uri, "#%s", id_attr);

        refNode = xmlSecTmplSignatureAddReference(signNode, xmlSecTransformSha256Id,
                                            NULL, BAD_CAST uri, NULL);
        if(refNode == NULL) {
            fprintf(stderr, "Error: failed to add reference to signature template\n");
            goto done;
        }

        /* add <dsig:KeyInfo/> and <dsig:X509Data/> */
        keyInfoNode = xmlSecTmplSignatureEnsureKeyInfo(signNode, NULL);
        if(keyInfoNode == NULL) {
            fprintf(stderr, "Error: failed to add key info\n");
            goto done;
        }

        x509DataNode = xmlSecTmplKeyInfoAddX509Data(keyInfoNode);
        if(x509DataNode == NULL) {
            fprintf(stderr, "Error: failed to add X509Data node\n");
            goto done;
        }

        if(xmlSecTmplX509DataAddSubjectName(x509DataNode) == NULL) {
            fprintf(stderr, "Error: failed to add X509SubjectName node\n");
            goto done;
        }

        if(xmlSecTmplX509DataAddCertificate(x509DataNode) == NULL) {
            fprintf(stderr, "Error: failed to add X509Certificate node\n");
            goto done;
        }

        /* add ID attributes to the doc context since we don't have DTDs */
        xmlSecAddIDs(doc, NULL, id_attributes);

        /* 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 = xmlSecCryptoAppKeyLoadEx(key_file, xmlSecKeyDataTypePrivate, xmlSecKeyDataFormatPem, NULL, NULL, NULL);
        if(dsigCtx->signKey == NULL) {
            fprintf(stderr,"Error: failed to load private pem key from \"%s\"\n", key_file);
            goto done;
        }

        /* load certificate and add to the key */
        if(xmlSecCryptoAppKeyCertLoad(dsigCtx->signKey, cert_file, xmlSecKeyDataFormatPem) < 0) {
            fprintf(stderr,"Error: failed to load pem certificate \"%s\"\n", cert_file);
            goto done;
        }

        /* set key name to the file name, this is just an example! */
        if(xmlSecKeySetName(dsigCtx->signKey, BAD_CAST 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);
    }

### sign4-doc.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <!--
    XML Security Library example: Original XML doc file for sign3 example.
    -->
    <Envelope xmlns="urn:envelope">
      <Data ID="data">
    	Hello, World!
      </Data>
    </Envelope>

### sign4-res.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <!--
    XML Security Library example: Original XML doc file for sign3 example.
    -->
    <Envelope xmlns="urn:envelope">
      <Data ID="data">
    	Hello, World!
      </Data>
    <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo>
    <CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
    <SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
    <Reference URI="#data">
    <DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
    <DigestValue>eZuEhA6xeEm+T9S3q5P/NQ8Mphp1zSAFhnBbiHN4IeE=</DigestValue>
    </Reference>
    </SignedInfo>
    <SignatureValue>OlxLIdZJDjjgYak2F7udevdsY2fjCksQ8UXsB9qXLyDUvG9UcDqhbKwtukVUTzE7
    H84ofXx2RnJiF5Bcq4arsA==</SignatureValue>
    <KeyInfo>
    <X509Data>
    <X509SubjectName>emailAddress=xmlsec@aleksey.com,CN=Aleksey Sanin,OU=Test Third Level RSA Certificate,O=XML Security Library (http://www.aleksey.com/xmlsec),ST=California,C=US</X509SubjectName>
    <X509Certificate>MIIDpzCCA1GgAwIBAgIJAK+ii7kzrdqvMA0GCSqGSIb3DQEBBQUAMIGcMQswCQYD
    VQQGEwJVUzETMBEGA1UECBMKQ2FsaWZvcm5pYTE9MDsGA1UEChM0WE1MIFNlY3Vy
    aXR5IExpYnJhcnkgKGh0dHA6Ly93d3cuYWxla3NleS5jb20veG1sc2VjKTEWMBQG
    A1UEAxMNQWxla3NleSBTYW5pbjEhMB8GCSqGSIb3DQEJARYSeG1sc2VjQGFsZWtz
    ZXkuY29tMCAXDTE0MDUyMzE3NTUzNFoYDzIxMTQwNDI5MTc1NTM0WjCBxzELMAkG
    A1UEBhMCVVMxEzARBgNVBAgTCkNhbGlmb3JuaWExPTA7BgNVBAoTNFhNTCBTZWN1
    cml0eSBMaWJyYXJ5IChodHRwOi8vd3d3LmFsZWtzZXkuY29tL3htbHNlYykxKTAn
    BgNVBAsTIFRlc3QgVGhpcmQgTGV2ZWwgUlNBIENlcnRpZmljYXRlMRYwFAYDVQQD
    Ew1BbGVrc2V5IFNhbmluMSEwHwYJKoZIhvcNAQkBFhJ4bWxzZWNAYWxla3NleS5j
    b20wXDANBgkqhkiG9w0BAQEFAANLADBIAkEA09BtD3aeVt6DVDkk0dI7Vh7Ljqdn
    sYmW0tbDVxxK+nume+Z9Sb4znbUKkWl+vgQATdRUEyhT2P+Gqrd0UBzYfQIDAQAB
    o4IBRTCCAUEwDAYDVR0TBAUwAwEB/zAsBglghkgBhvhCAQ0EHxYdT3BlblNTTCBH
    ZW5lcmF0ZWQgQ2VydGlmaWNhdGUwHQYDVR0OBBYEFNf0xkZ3zjcEI60pVPuwDqTM
    QygZMIHjBgNVHSMEgdswgdiAFP7k7FMk8JWVxxC14US1XTllWuN+oYG0pIGxMIGu
    MQswCQYDVQQGEwJVUzETMBEGA1UECBMKQ2FsaWZvcm5pYTE9MDsGA1UEChM0WE1M
    IFNlY3VyaXR5IExpYnJhcnkgKGh0dHA6Ly93d3cuYWxla3NleS5jb20veG1sc2Vj
    KTEQMA4GA1UECxMHUm9vdCBDQTEWMBQGA1UEAxMNQWxla3NleSBTYW5pbjEhMB8G
    CSqGSIb3DQEJARYSeG1sc2VjQGFsZWtzZXkuY29tggkAr6KLuTOt2q0wDQYJKoZI
    hvcNAQEFBQADQQAOXBj0yICp1RmHXqnUlsppryLCW3pKBD1dkb4HWarO7RjA1yJJ
    fBjXssrERn05kpBcrRfzou4r3DCgQFPhjxga
    </X509Certificate>
    </X509Data>
    </KeyInfo>
    </Signature></Envelope>