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Verifing and decrypting documents.
Since the template is just an XML file, it might be created in advance
and saved in a file. It's also possible for application to create
templates without using XML Security Library functions. Also in some
cases template should be inserted in the signed or encrypted data
(for example, if you want to create an enveloped or enveloping
signature).
Signature verification and data decryption do not require template
because all the necessary information is provided in the signed or
encrypted document.
Verifying a signed document
The typical siganture verification process includes following steps:
Example 9. Verifying a document.
/**
* verify_file:
* @xml_file: the signed XML file name.
* @key_file: the PEM public key file name.
*
* Verifies XML signature in #xml_file using public key from #key_file.
*
* Returns 0 on success or a negative value if an error occurs.
*/
int
verify_file(const char* xml_file, const char* key_file) {
xmlDocPtr doc = NULL;
xmlNodePtr node = NULL;
xmlSecDSigCtxPtr dsigCtx = NULL;
int res = -1;
assert(xml_file);
assert(key_file);
/* load file */
doc = xmlParseFile(xml_file);
if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
goto done;
}
/* find start node */
node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeSignature, xmlSecDSigNs);
if(node == NULL) {
fprintf(stderr, "Error: start node not found in \"%s\"\n", xml_file);
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 public key */
dsigCtx->signKey = xmlSecCryptoAppPemKeyLoad(key_file, NULL, NULL);
if(dsigCtx->signKey == NULL) {
fprintf(stderr,"Error: failed to load public 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;
}
/* Verify signature */
if(xmlSecDSigCtxVerify(dsigCtx, node) < 0) {
fprintf(stderr,"Error: signature verify\n");
goto done;
}
/* print verification result to stdout */
if(dsigCtx->status == xmlSecDSigStatusSucceeded) {
fprintf(stdout, "Signature is OK\n");
} else {
fprintf(stdout, "Signature is INVALID\n");
}
/* success */
res = 0;
done:
/* cleanup */
if(dsigCtx != NULL) {
xmlSecDSigCtxDestroy(dsigCtx);
}
if(doc != NULL) {
xmlFreeDoc(doc);
}
return(res);
}
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Decrypting an encrypted document
The typical decryption process includes following steps:
Example 10. Decrypting a document.
int
decrypt_file(const char* enc_file, const char* key_file) {
xmlDocPtr doc = NULL;
xmlNodePtr node = NULL;
xmlSecEncCtxPtr encCtx = NULL;
int res = -1;
assert(enc_file);
assert(key_file);
/* load template */
doc = xmlParseFile(enc_file);
if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
fprintf(stderr, "Error: unable to parse file \"%s\"\n", enc_file);
goto done;
}
/* find start node */
node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeEncryptedData, xmlSecEncNs);
if(node == NULL) {
fprintf(stderr, "Error: start node not found in \"%s\"\n", enc_file);
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 */
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;
}
/* decrypt the data */
if((xmlSecEncCtxDecrypt(encCtx, node) < 0) || (encCtx->result == NULL)) {
fprintf(stderr,"Error: decryption failed\n");
goto done;
}
/* print decrypted data to stdout */
if(encCtx->resultReplaced != 0) {
fprintf(stdout, "Decrypted XML data:\n");
xmlDocDump(stdout, doc);
} else {
fprintf(stdout, "Decrypted binary data (%d bytes):\n", xmlSecBufferGetSize(encCtx->result));
if(xmlSecBufferGetData(encCtx->result) != NULL) {
fwrite(xmlSecBufferGetData(encCtx->result),
1,
xmlSecBufferGetSize(encCtx->result),
stdout);
}
}
fprintf(stdout, "\n");
/* success */
res = 0;
done:
/* cleanup */
if(encCtx != NULL) {
xmlSecEncCtxDestroy(encCtx);
}
if(doc != NULL) {
xmlFreeDoc(doc);
}
return(res);
}
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Aleksey Sanin
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