Very difficult to find definitive info on this.
From what I can find on google and looking at BIP32 it seems like the process to calculate a checksum for an extended key is to decode the base58 string to data, then perform a double sha256 on the data and the first 4 bytes from the double hash are the checksum.
I am trying to take in a non xpub (vpubs, upub ypub etc) and convert it to an xpub/tpub programmatically. Currently I have it working but the last 6 digits of the xpub are always incorrect, I am assuming this is the checksum?
In order to correctly calculate the checksum do I remove the prefix first, then remove the existing checksum then do the double sha256 on the stripped down extended key or do I keep the new xpub prefix and then perform the double sha256? Or am I completely wrong in my assumptions here?
Thanks in advanced!