Old version (2013): github.com/bitcoin/bitcoin/blob/16b3ff66e0137b68de0d08ad88ce9798bce2d68d/src/wallet.cpp#L258-L268
The earliest possible date is Sep 2011 since wallet encryption was introduced in v0.4.0 which was released on that date.
Here's the code: github.com/bitcoin/bitcoin/blob/b7bcaf940d27fa8cfe89422943fbeaab7a350930/src/wallet.cpp#L155-L158 (wallet encryption pt2)
TL;DR: It's the same.
Thanks.
We are discussing 'wallet.dat files for sale' in other groups (telegram) and want to find fake wallets. I had the idea to check the rounds (iteration) of these wallets as I saw some with values < 25000 and now we can say that these wallets are fake. The producers of such wallets didn't know that wallets with iteration < 25000 can't be generated with Bitcoin Core
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