Fix subscript[0] potential bugs in key.cpp

Author: JeremyRubin

src/key.cpp

@@ -138,7 +138,7 @@ CPrivKey CKey::GetPrivKey() const {
     size_t privkeylen;
     privkey.resize(279);
     privkeylen = 279;
-    ret = ec_privkey_export_der(secp256k1_context_sign, (unsigned char*)&privkey[0], &privkeylen, begin(), fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
+    ret = ec_privkey_export_der(secp256k1_context_sign, (unsigned char*) privkey.data(), &privkeylen, begin(), fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
     assert(ret);
     privkey.resize(privkeylen);
     return privkey;
@@ -167,7 +167,7 @@ bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, uint32_
     secp256k1_ecdsa_signature sig;
     int ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), begin(), secp256k1_nonce_function_rfc6979, test_case ? extra_entropy : NULL);
     assert(ret);
-    secp256k1_ecdsa_signature_serialize_der(secp256k1_context_sign, (unsigned char*)&vchSig[0], &nSigLen, &sig);
+    secp256k1_ecdsa_signature_serialize_der(secp256k1_context_sign, (unsigned char*)vchSig.data(), &nSigLen, &sig);
     vchSig.resize(nSigLen);
     return true;
 }
@@ -202,7 +202,7 @@ bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig)
 }
 
 bool CKey::Load(CPrivKey &privkey, CPubKey &vchPubKey, bool fSkipCheck=false) {
-    if (!ec_privkey_import_der(secp256k1_context_sign, (unsigned char*)begin(), &privkey[0], privkey.size()))
+    if (!ec_privkey_import_der(secp256k1_context_sign, (unsigned char*)begin(), privkey.data(), privkey.size()))
         return false;
     fCompressed = vchPubKey.IsCompressed();
     fValid = true;
@@ -245,8 +245,8 @@ void CExtKey::SetMaster(const unsigned char *seed, unsigned int nSeedLen) {
     static const unsigned char hashkey[] = {'B','i','t','c','o','i','n',' ','s','e','e','d'};
     std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
     CHMAC_SHA512(hashkey, sizeof(hashkey)).Write(seed, nSeedLen).Finalize(vout.data());
-    key.Set(&vout[0], &vout[32], true);
-    memcpy(chaincode.begin(), &vout[32], 32);
+    key.Set(vout.data(), vout.data() + 32, true);
+    memcpy(chaincode.begin(), vout.data() + 32, 32);
     nDepth = 0;
     nChild = 0;
     memset(vchFingerprint, 0, sizeof(vchFingerprint));