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Merge bitcoin/bitcoin#35606: script: qa: Improve Key::Fingerprint type safety

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c9a70f9338 script: qa: Improve Key::Fingerprint type safety (David Gumberg)

Pull request description:

  Extracted from pseudoramdom's work in #35436:

  Instead of using c style arrays for key fingerprints, use `std::array`'s whose length can always reasoned about at compile time and for most operations the compiler enforces the size being correct.

  ```cpp
  using KeyFingerprint = std::array<unsigned char, 4>;
  ```

  ```diff
  -    unsigned char vchFingerprint[4];
  +    KeyFingerprint fingerprint;
  ```

  This allows the replacement of a lot of raw `memcpy` + trust-me-bro lengths, with the assignment operator:

  ```cpp
  -    memcpy(ret.vchFingerprint, vchFingerprint, 4);
  +    ret.fingerprint = fingerprint;
  ```

  This commit also adds two helper functions for
  - Retrieving the [fingerprint of a key identifier](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#user-content-Key_identifiers) (`CKeyID`)
  - Retrieving the fingerprint of the key identifier of an XPUB.

ACKs for top commit:
  w0xlt:
    ACK c9a70f9338
  sedited:
    ACK c9a70f9338
  pseudoramdom:
    Code review ACK w/ some minor nits c9a70f9338
  polespinasa:
    ACK c9a70f9338

Tree-SHA512: 3ee76742c0bc317dfbc12a6731afdcc40495db6e4d5d94880d0a721990d36cb3e4d374ccc96079ba1f8ad3f88581ee5a609bfe259c0ea7cd28cade373aac1b38
This commit is contained in:
merge-script
2026-07-29 09:55:39 +02:00
parent a9d181f2d3 c9a70f9338
commit 8ecbe270f0
11 changed files with 56 additions and 52 deletions
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13
src/key.cpp
View File

@@ -359,8 +359,7 @@ CKey GenerateRandomKey(bool compressed) noexcept
bool CExtKey::Derive(CExtKey &out, unsigned int _nChild) const {
if (nDepth == std::numeric_limits<unsigned char>::max()) return false;
out.nDepth = nDepth + 1;
CKeyID id = key.GetPubKey().GetID();
memcpy(out.vchFingerprint, &id, 4);
out.fingerprint = id_key_fingerprint();
out.nChild = _nChild;
return key.Derive(out.key, out.chaincode, _nChild, chaincode);
}
@@ -375,13 +374,13 @@ void CExtKey::SetSeed(std::span<const std::byte> seed)
memcpy(chaincode.begin(), vout.data() + 32, 32);
nDepth = 0;
nChild = 0;
memset(vchFingerprint, 0, sizeof(vchFingerprint));
fingerprint.fill(0);
}
CExtPubKey CExtKey::Neuter() const {
CExtPubKey ret;
ret.nDepth = nDepth;
memcpy(ret.vchFingerprint, vchFingerprint, 4);
ret.fingerprint = fingerprint;
ret.nChild = nChild;
ret.pubkey = key.GetPubKey();
ret.chaincode = chaincode;
@@ -390,7 +389,7 @@ CExtPubKey CExtKey::Neuter() const {
void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
code[0] = nDepth;
memcpy(code+1, vchFingerprint, 4);
std::ranges::copy(fingerprint, code+1);
WriteBE32(code+5, nChild);
memcpy(code+9, chaincode.begin(), 32);
code[41] = 0;
@@ -400,11 +399,11 @@ void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
void CExtKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
nDepth = code[0];
memcpy(vchFingerprint, code+1, 4);
std::copy_n(code + 1, fingerprint.size(), fingerprint.begin());
nChild = ReadBE32(code+5);
memcpy(chaincode.begin(), code+9, 32);
key.Set(code+42, code+BIP32_EXTKEY_SIZE, true);
if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || code[41] != 0) key = CKey();
if ((nDepth == 0 && (nChild != 0 || ReadLE32(fingerprint.data()) != 0)) || code[41] != 0) key = CKey();
}
KeyPair::KeyPair(const CKey& key, const uint256* merkle_root)