4.3.1.17  modifyVerifier (Modification Verifier)

Anybody knows how exactly is hash calculated?

Given password, how output from pre-processing step is appended with salt and if there is any operation inside spin count loop.

Anyone here able to write pseudo-code?

have you looked at the 'Office Open XML Part 4 - Markup Language Reference_final' document. I looked up the tag, and in that section is information to answer all of your questions, but ill go over them real quick.


how is hash calculated: You define the specific algorithm used by the generating application in the attribute named 'cryptAlgorithmSid'  (Cryptographic Hashing Algorithm). There is a table in the reference documnet that has mappings from a given int value to the algorithm used for example cryptAlgorithmSid=4 means that it uses the SHA-1 algorithm.

Salt: 'saltData' is the attribute that lets you define what salt gets added to the user provided     password before hashing.
    "Specifies the salt which was prepended to the user-supplied password before it was hashed using the hashing algorithm defined by the preceding attribute values to generate the hashData attribute, and which shall also be prepended to the user-supplied password before attempting to generate a hash value for comparison. "(from reference doc)


spin count: "Specifies the number of times the hashing function shall be iteratively run (using each iteration's result as the input for the next iteration) when attempting to compare a user-supplied password with the value stored in the hashData attribute" (from reference doc)

there is a link to the reference documents on the ooxmldeveloper homepage.

sure I checked - as you can see chapter number (4.3.1.17) in my first post...

Anyway - I am not sure specification is correct/clear regarding this algorithm.

I have all bits and pieces working:
- SHA-1 (seems to be always used)
- base64 decoding and encoding
- pre-processing algorithm is ok (Excel 2007 uses low 2 bytes of result for checking validity of given password)

I have tried append/perpend salt, reversed and non-reversed output from pre-hashing, append as hex string, use clear password with salt ... many different permutations ... but I was unable to re-generate correct hash value.

I am afraid only someone with access to source code can give me correct answer... or someone more lucky than I am...