Question

I’m implementing the SHA1 algorithm from the pseudocode on wikipedia.

It says I should append to original length as 64 bits to the message, so I tried the following:

// new_message is of type char[] and is 9+ bytes long
*((__int64*)(new_message-8)) = (__int64) length;

This makes the new_message’s memory corrupt.

Could someone spot the error?

Thanks!

Edit:

Jesus, I’m so stupid. new_message pointed to the start of my array, no wonder it crashed!

Answer 1

Not definitively, without seeing the part of the code that shows what new_message is set to.

It looks like you are underflowing the buffer though, which will mess up the heap header that probably precedes &new_message[0]. You are writing your __int64 8 bytes before the start of the char[], by the look of things.