feat: added back in private keys from BIP32 Seed (dashpay#29)

* feat: added back in private keys from BIP32 Seed

* feat: added in unit test

Author: QuantumExplorer

src/privatekey.cpp

@@ -19,6 +19,35 @@ namespace bls {
 
 const size_t PrivateKey::PRIVATE_KEY_SIZE;
 
+PrivateKey PrivateKey::FromSeedBIP32(const Bytes& seed) {
+    // "BLS private key seed" in ascii
+    const uint8_t hmacKey[] = {66, 76, 83, 32, 112, 114, 105, 118, 97, 116, 101,
+                               32, 107, 101, 121, 32, 115, 101, 101, 100};
+
+    auto* hash = Util::SecAlloc<uint8_t>(
+        PrivateKey::PRIVATE_KEY_SIZE);
+
+    // Hash the seed into sk
+    md_hmac(hash, seed.begin(), (int)seed.size(), hmacKey, sizeof(hmacKey));
+
+    bn_t order;
+    bn_new(order);
+    g1_get_ord(order);
+
+    // Make sure private key is less than the curve order
+    bn_t* skBn = Util::SecAlloc<bn_t>(1);
+    bn_new(*skBn);
+    bn_read_bin(*skBn, hash, PrivateKey::PRIVATE_KEY_SIZE);
+    bn_mod_basic(*skBn, *skBn, order);
+
+    PrivateKey k;
+    bn_copy(k.keydata, *skBn);
+
+    Util::SecFree(skBn);
+    Util::SecFree(hash);
+    return k;
+}
+
 // Construct a private key from a bytearray.
 PrivateKey PrivateKey::FromBytes(const Bytes& bytes, bool modOrder)
 {

src/privatekey.hpp

@@ -31,6 +31,9 @@ class PrivateKey {
     // less than the group order (which is in bls.hpp).
     static const size_t PRIVATE_KEY_SIZE = 32;
 
+    // Construct a private key from a BIP32 based seed.
+    static PrivateKey FromSeedBIP32(const Bytes& seed);
+
     // Construct a private key from a bytearray.
     static PrivateKey FromBytes(const Bytes& bytes, bool modOrder = false);
 

src/test.cpp

@@ -121,6 +121,13 @@ TEST_CASE("class PrivateKey") {
         REQUIRE_THROWS(PrivateKey::FromBytes(Bytes(buffer, PrivateKey::PRIVATE_KEY_SIZE), false));
         REQUIRE_NOTHROW(PrivateKey::FromBytes(Bytes(buffer, PrivateKey::PRIVATE_KEY_SIZE), true));
     }
+    SECTION("BIP32 Seed") {
+        uint8_t aliceSeed[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        PrivateKey pk1 = PrivateKey::FromSeedBIP32(Bytes(aliceSeed, 10));
+        vector<uint8_t> privateKey = pk1.Serialize(true);
+        vector<uint8_t> knownPrivateKey = Util::HexToBytes("46891c2cec49593c81921e473db7480029e0fc1eb933c6b93d81f5370eb19fbd");
+        REQUIRE(privateKey == knownPrivateKey);
+    }
     SECTION("keydata checks") {
         PrivateKey pk1 = PrivateKey::FromByteVector(getRandomSeed(), true);
         G1Element g1 = pk1.GetG1Element();