Question

I need to implement the MD5 checksum to verify a MD5 checksum in a XML file including all XML tags and which has received from our client. The length of the received MD5 checksum is 32 byte hexadecimal digits.

We need set MD5 Checksum field should be 0 in received XML file prior to checksum calculation and we have to indepandantly calculate and verify the MD5 checksum value in a received XML file.

Our application is implemented in C. Please assist me on how to implement this.

Thanks

Answer 1

This directly depends on the library used for XML parsing. This is tricky however, because you can’t embed the MD5 in the XML file itself, for after embedding the checksum inside, unless you do the checksum only from the specific elements. As I understand you receive the MD5 independently? Is it calculated from the whole file, or only the tags/content?

• MD5 Public Domain code link – http://www.fourmilab.ch/md5/
• XML library for C – http://xmlsoft.org/

Exact solutions depend on the code used.

Based on your comment you need to do the following steps:

• load the xml file (possibly even as plain-text) read the MD5
• substitute the MD5 in the file with zero, write the file down (or better to memory)
• run MD5 on the pure file data and compare it with the value stored before