Generating an XML document hash in C#

Question

What's the best way to go about hashing an XML document in C#? I'd like to hash an XML document so that I can tell if it was manually changed from when it was generated. I'm not using this for security--it's OK if someone changes the XML, and changes the hash to match.

For example, I'd hash the child nodes of the root and store the hash as an attribute of the root:

<RootNode Hash="abc123">
    <!-- Content to hash here -->
</RootNode>

Answer 1

You can use the cryptography name space:

System.Security.Cryptography.MACTripleDES hash = new System.Security.Cryptography.MACTripleDES(Encoding.Default.GetBytes("mykey"));
string hashString = Convert.ToBase64String(hash.ComputeHash(Encoding.Default.GetBytes(myXMLString)));

You just need to use a key to create the hashing cryptographer and then create a hash with the string reqpresentation of your xml.

Answer 2

.NET has classes that implement the XML digital signature spec. The signature can be added inside the original XML document (i.e. an "enveloped signature"), or stored/transferred separately.

It may be a bit overkill since you don't need the security, but it has the advantage of being already implemented, and being a standard which does not depend on a language or platform.