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[docs] Add doxygen comment for CKeyPool

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jnewbery committed Apr 9, 2019
1 parent ef2d515 commit 37796b2dd49772b17ff39a1a71b73f6d2248ac6d
Showing with 50 additions and 3 deletions.
  1. +50 −3 src/wallet/wallet.h
@@ -135,14 +135,61 @@ enum WalletFlags : uint64_t {

static constexpr uint64_t g_known_wallet_flags = WALLET_FLAG_DISABLE_PRIVATE_KEYS | WALLET_FLAG_BLANK_WALLET | WALLET_FLAG_KEY_ORIGIN_METADATA;

/** A key pool entry */
/** A key from a CWallet's keypool
*
* The wallet holds one (for pre HD-split wallets) or several keypools. These
* are sets of keys that have not yet been used to provide addresses or receive
* change.
*
* The Bitcoin Core wallet was originally a collection of unrelated private
* keys with their associated addresses. If a non-HD wallet generated a
* key/address, gave that address out and then restored a backup from before
* that key's generation, then any funds sent to that address would be
* lost definitively.
*
* The keypool was implemented to avoid this scenario (commit: 10384941). The
* wallet would generate a set of keys (100 by default). When a new public key
* was required, either to give out as an address or to use in a change output,
* it would be drawn from the keypool. The keypool would then be topped up to
* maintain 100 keys. This ensured that as long as the wallet hadn't used more
* than 100 keys since the previous backup, all funds would be safe, since a
* restored wallet would be able to scan for all owned addresses.
*
* A keypool also allowed encrypted wallets to give out addresses without
* having to be decrypted to generate a new private key.
*
* With the introduction of HD wallets (commit: f1902510), the keypool
* essentially became an address look-ahead pool. Restoring old backups can no
* longer definitively lose funds as long as the addresses used were from the
* wallet's HD seed (since all private keys can be rederived from the seed).
* However, if many addresses were used since the backup, then the wallet may
* not know how far ahead in the HD chain to look for its addresses. The
* keypool is used to implement a 'gap limit'. The keypool maintains a set of
* keys (by default 1000) ahead of the last used key and scans for the
* addresses of those keys. This avoids the risk of not seeing transactions
* involving the wallet's addresses, or of re-using the same address.
*
* The HD-split wallet feature added a second keypool (commit: 02592f4c). There
* is an external keypool (for addresses to hand out) and an internal keypool
* (for change addresses).
*
* Keypool keys are stored in the wallet/keystore's keymap. The keypool data is
* stored as sets of indexes in the wallet (setInternalKeyPool,
* setExternalKeyPool and set_pre_split_keypool), and a map from the key to the
* index (m_pool_key_to_index). The CKeyPool object is used to
* serialize/deserialize the pool data to/from the database.
*/
class CKeyPool
{
public:
//! The time at which the key was generated. Set in AddKeypoolPubKeyWithDB
int64_t nTime;
//! The public key
CPubKey vchPubKey;
bool fInternal; // for change outputs
bool m_pre_split; // For keys generated before keypool split upgrade
//! Whether this keypool entry is in the internal keypool (for change outputs)
bool fInternal;
//! Whether this key was generated for a keypool before the wallet was upgraded to HD-split
bool m_pre_split;

CKeyPool();
CKeyPool(const CPubKey& vchPubKeyIn, bool internalIn);

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