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descriptors: Cache last hardened xpub
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Cache the last hardenex xpub in the DescriptorCache
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@achow101
achow101 committed Jun 24, 2021
1 parent cacc391 commit d87b544
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Showing 2 changed files with 61 additions and 3 deletions.
48 changes: 45 additions & 3 deletions src/script/descriptor.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -302,11 +302,14 @@ class BIP32PubkeyProvider final : public PubkeyProvider
}

// Derives the last xprv
bool GetDerivedExtKey(const SigningProvider& arg, CExtKey& xprv) const
bool GetDerivedExtKey(const SigningProvider& arg, CExtKey& xprv, CExtKey& last_hardened) const
{
if (!GetExtKey(arg, xprv)) return false;
for (auto entry : m_path) {
xprv.Derive(xprv, entry);
if (entry >> 31) {
last_hardened = xprv;
}
}
return true;
}
Expand Down Expand Up @@ -340,6 +343,7 @@ class BIP32PubkeyProvider final : public PubkeyProvider
// Derive keys or fetch them from cache
CExtPubKey final_extkey = m_root_extkey;
CExtPubKey parent_extkey = m_root_extkey;
CExtPubKey last_hardened_extkey;
bool der = true;
if (read_cache) {
if (!read_cache->GetCachedDerivedExtPubKey(m_expr_index, pos, final_extkey)) {
Expand All @@ -351,11 +355,15 @@ class BIP32PubkeyProvider final : public PubkeyProvider
}
} else if (IsHardened()) {
CExtKey xprv;
if (!GetDerivedExtKey(arg, xprv)) return false;
CExtKey lh_xprv;
if (!GetDerivedExtKey(arg, xprv, lh_xprv)) return false;
parent_extkey = xprv.Neuter();
if (m_derive == DeriveType::UNHARDENED) der = xprv.Derive(xprv, pos);
if (m_derive == DeriveType::HARDENED) der = xprv.Derive(xprv, pos | 0x80000000UL);
final_extkey = xprv.Neuter();
if (lh_xprv.key.IsValid()) {
last_hardened_extkey = lh_xprv.Neuter();
}
} else {
for (auto entry : m_path) {
der = parent_extkey.Derive(parent_extkey, entry);
Expand All @@ -374,6 +382,10 @@ class BIP32PubkeyProvider final : public PubkeyProvider
// Only cache parent if there is any unhardened derivation
if (m_derive != DeriveType::HARDENED) {
write_cache->CacheParentExtPubKey(m_expr_index, parent_extkey);
// Cache last hardened xpub if we have it
if (last_hardened_extkey.pubkey.IsValid()) {
write_cache->CacheLastHardenedExtPubKey(m_expr_index, last_hardened_extkey);
}
} else if (final_info_out.path.size() > 0) {
write_cache->CacheDerivedExtPubKey(m_expr_index, pos, final_extkey);
}
Expand Down Expand Up @@ -454,7 +466,8 @@ class BIP32PubkeyProvider final : public PubkeyProvider
bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const override
{
CExtKey extkey;
if (!GetDerivedExtKey(arg, extkey)) return false;
CExtKey dummy;
if (!GetDerivedExtKey(arg, extkey, dummy)) return false;
if (m_derive == DeriveType::UNHARDENED) extkey.Derive(extkey, pos);
if (m_derive == DeriveType::HARDENED) extkey.Derive(extkey, pos | 0x80000000UL);
key = extkey.key;
Expand Down Expand Up @@ -1400,6 +1413,11 @@ void DescriptorCache::CacheDerivedExtPubKey(uint32_t key_exp_pos, uint32_t der_i
xpubs[der_index] = xpub;
}

void DescriptorCache::CacheLastHardenedExtPubKey(uint32_t key_exp_pos, const CExtPubKey& xpub)
{
m_last_hardened_xpubs[key_exp_pos] = xpub;
}

bool DescriptorCache::GetCachedParentExtPubKey(uint32_t key_exp_pos, CExtPubKey& xpub) const
{
const auto& it = m_parent_xpubs.find(key_exp_pos);
Expand All @@ -1418,6 +1436,14 @@ bool DescriptorCache::GetCachedDerivedExtPubKey(uint32_t key_exp_pos, uint32_t d
return true;
}

bool DescriptorCache::GetCachedLastHardenedExtPubKey(uint32_t key_exp_pos, CExtPubKey& xpub) const
{
const auto& it = m_last_hardened_xpubs.find(key_exp_pos);
if (it == m_last_hardened_xpubs.end()) return false;
xpub = it->second;
return true;
}

DescriptorCache DescriptorCache::MergeAndDiff(const DescriptorCache& other)
{
DescriptorCache diff;
Expand Down Expand Up @@ -1445,6 +1471,17 @@ DescriptorCache DescriptorCache::MergeAndDiff(const DescriptorCache& other)
diff.CacheDerivedExtPubKey(derived_xpub_map_pair.first, derived_xpub_pair.first, derived_xpub_pair.second);
}
}
for (const auto& lh_xpub_pair : other.GetCachedLastHardenedExtPubKeys()) {
CExtPubKey xpub;
if (GetCachedLastHardenedExtPubKey(lh_xpub_pair.first, xpub)) {
if (xpub != lh_xpub_pair.second) {
throw std::runtime_error(std::string(__func__) + ": New cached last hardened xpub does not match already cached last hardened xpub");
}
continue;
}
CacheLastHardenedExtPubKey(lh_xpub_pair.first, lh_xpub_pair.second);
diff.CacheLastHardenedExtPubKey(lh_xpub_pair.first, lh_xpub_pair.second);
}
return diff;
}

Expand All @@ -1457,3 +1494,8 @@ const std::unordered_map<uint32_t, ExtPubKeyMap> DescriptorCache::GetCachedDeriv
{
return m_derived_xpubs;
}

const ExtPubKeyMap DescriptorCache::GetCachedLastHardenedExtPubKeys() const
{
return m_last_hardened_xpubs;
}
16 changes: 16 additions & 0 deletions src/script/descriptor.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@ class DescriptorCache {
std::unordered_map<uint32_t, ExtPubKeyMap> m_derived_xpubs;
/** Map key expression index -> parent xpub */
ExtPubKeyMap m_parent_xpubs;
/** Map key expression index -> last hardened xpub */
ExtPubKeyMap m_last_hardened_xpubs;

public:
/** Cache a parent xpub
Expand Down Expand Up @@ -50,11 +52,25 @@ class DescriptorCache {
* @param[in] xpub The CExtPubKey to get from cache
*/
bool GetCachedDerivedExtPubKey(uint32_t key_exp_pos, uint32_t der_index, CExtPubKey& xpub) const;
/** Cache a last hardened xpub
*
* @param[in] key_exp_pos Position of the key expression within the descriptor
* @param[in] xpub The CExtPubKey to cache
*/
void CacheLastHardenedExtPubKey(uint32_t key_exp_pos, const CExtPubKey& xpub);
/** Retrieve a cached last hardened xpub
*
* @param[in] key_exp_pos Position of the key expression within the descriptor
* @param[in] xpub The CExtPubKey to get from cache
*/
bool GetCachedLastHardenedExtPubKey(uint32_t key_exp_pos, CExtPubKey& xpub) const;

/** Retrieve all cached parent xpubs */
const ExtPubKeyMap GetCachedParentExtPubKeys() const;
/** Retrieve all cached derived xpubs */
const std::unordered_map<uint32_t, ExtPubKeyMap> GetCachedDerivedExtPubKeys() const;
/** Retrieve all cached last hardened xpubs */
const ExtPubKeyMap GetCachedLastHardenedExtPubKeys() const;

/** Combine another DescriptorCache into this one.
* Returns a cache containing the items from the other cache unknown to current cache
Expand Down

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