From 89bc6418b1f16880af38cbd2f27759b972138169 Mon Sep 17 00:00:00 2001
From: SChernykh <sergey.v.chernykh@gmail.com>
Date: Wed, 16 Jun 2021 00:10:34 +0200
Subject: [PATCH] Secret key derivation

---
 src/base/tools/cryptonote/Signatures.cpp | 51 +++++++++++++++++++++++-
 src/base/tools/cryptonote/Signatures.h   |  3 ++
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/base/tools/cryptonote/Signatures.cpp b/src/base/tools/cryptonote/Signatures.cpp
index ced225616..8c44fe699 100644
--- a/src/base/tools/cryptonote/Signatures.cpp
+++ b/src/base/tools/cryptonote/Signatures.cpp
@@ -77,6 +77,27 @@ static void hash_to_scalar(const void* data, size_t length, ec_scalar& res)
 }
 
 
+static void derivation_to_scalar(const uint8_t* derivation, size_t output_index, ec_scalar& res)
+{
+    struct {
+        uint8_t derivation[32];
+        uint8_t output_index[(sizeof(size_t) * 8 + 6) / 7];
+    } buf;
+
+    uint8_t* end = buf.output_index;
+    memcpy(buf.derivation, derivation, sizeof(buf.derivation));
+
+    size_t k = output_index;
+    while (k >= 0x80) {
+        *(end++) = (static_cast<uint8_t>(k) & 0x7F) | 0x80;
+        k >>= 7;
+    }
+    *(end++) = static_cast<uint8_t>(k);
+
+    hash_to_scalar(&buf, end - reinterpret_cast<uint8_t*>(&buf), res);
+}
+
+
 namespace xmrig {
 
 
@@ -130,8 +151,9 @@ bool check_signature(const uint8_t* prefix_hash, const uint8_t* pub, const uint8
     ge_tobytes((uint8_t*)&buf.comm, &tmp2);
 
     static const ec_point infinity = { { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} };
-    if (memcmp(&buf.comm, &infinity, 32) == 0)
+    if (memcmp(&buf.comm, &infinity, 32) == 0) {
         return false;
+    }
 
     hash_to_scalar(&buf, sizeof(s_comm), c);
     sc_sub((uint8_t*)&c, (uint8_t*)&c, (const uint8_t*)&sig.c);
@@ -140,5 +162,32 @@ bool check_signature(const uint8_t* prefix_hash, const uint8_t* pub, const uint8
 }
 
 
+bool generate_key_derivation(const uint8_t* key1, const uint8_t* key2, uint8_t* derivation)
+{
+    ge_p3 point;
+    ge_p2 point2;
+    ge_p1p1 point3;
+
+    if (ge_frombytes_vartime(&point, key1) != 0) {
+        return false;
+    }
+
+    ge_scalarmult(&point2, key2, &point);
+    ge_mul8(&point3, &point2);
+    ge_p1p1_to_p2(&point2, &point3);
+    ge_tobytes(derivation, &point2);
+
+    return true;
+}
+
+
+void derive_secret_key(const uint8_t* derivation, size_t output_index, const uint8_t* base, uint8_t* derived_key)
+{
+    ec_scalar scalar;
+
+    derivation_to_scalar(derivation, output_index, scalar);
+    sc_add(derived_key, base, (uint8_t*) &scalar);
+}
+
 
 } /* namespace xmrig */
diff --git a/src/base/tools/cryptonote/Signatures.h b/src/base/tools/cryptonote/Signatures.h
index a9db90462..7bc9755f6 100644
--- a/src/base/tools/cryptonote/Signatures.h
+++ b/src/base/tools/cryptonote/Signatures.h
@@ -31,6 +31,9 @@ namespace xmrig {
 void generate_signature(const uint8_t* prefix_hash, const uint8_t* pub, const uint8_t* sec, uint8_t* sig);
 bool check_signature(const uint8_t* prefix_hash, const uint8_t* pub, const uint8_t* sig);
 
+bool generate_key_derivation(const uint8_t* key1, const uint8_t* key2, uint8_t* derivation);
+void derive_secret_key(const uint8_t* derivation, size_t output_index, const uint8_t* base, uint8_t* derived_key);
+
 } /* namespace xmrig */