Mnemonic wallets stored the 32-byte BIP39 entropy as the HD seed and relied on
CHDChain.fMnemonicSeed to tell the deriver to expand it first. That flag is
version-gated in the CHDChain serialisation, so a binary that predates it reads
the record, never consumes the trailing byte, and derives from the raw entropy --
a different key tree, silently, with no error.
Store the expanded 64-byte BIP39 seed instead, with fMnemonic = false, and keep
the entropy in its own display-only record. Derivation then reads the stored
bytes directly on every binary, old or new, so key trees are identical and no
CHDChain version bump or minversion fence is needed. The wallet format stays
readable by earlier releases rather than becoming one-way.
Addresses are unchanged: the previous format expanded the entropy on every read
and fed the same 64 bytes to Master(). This is also the form the tree already
round-trips through -- z_exportwallet dumps the expanded seed, and restoring that
hex via -hdseed installs it with fMnemonic = false.
Write order is load-bearing: seed first, entropy second. A crash between them
leaves a wallet with a seed and no phrase, which is merely inconvenient. The
reverse would leave an entropy record with no seed, and the next start would mint
a different seed while the wallet still held a phrase for the old one.
-usemnemonic still defaults to false; only explicit opt-in and -mnemonic restores
take this path.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
DanS
20b2cbe830