add crypto/generators for direct access to canonical fixed generators

src/crypto/CMakeLists.txt

@@ -33,6 +33,7 @@ set(crypto_sources
   crypto-ops-data.c
   crypto-ops.c
   crypto.cpp
+  generators.cpp
   groestl.c
   hash-extra-blake.c
   hash-extra-groestl.c

src/crypto/generators.cpp

@@ -0,0 +1,186 @@
+// Copyright (c) 2022, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "generators.h"
+
+#include "crypto.h"
+extern "C"
+{
+#include "crypto-ops.h"
+}
+#include "hash.h"
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <mutex>
+
+namespace crypto
+{
+
+/// constexpr assert for old gcc bug: https://stackoverflow.com/questions/34280729/throw-in-constexpr-function
+/// - this function won't compile in a constexpr context if b == false
+constexpr void constexpr_assert(const bool b) { b ? 0 : throw std::runtime_error("constexpr assert failed"); };
+
+/// constexpr paste bytes into an array-of-bytes type
+template<typename T>
+constexpr T bytes_to(const std::initializer_list<unsigned char> bytes)
+{
+    T out{}; // zero-initialize trailing bytes
+
+    auto current = std::begin(out.data);
+    constexpr_assert(static_cast<long>(bytes.size()) <= std::end(out.data) - current);
+
+    for (const unsigned char byte : bytes)
+        *current++ = byte;
+    return out;
+}
+
+// generators
+//standard ed25519 generator G: {x, 4/5} (positive x when decompressing y = 4/5)
+constexpr public_key G = bytes_to<public_key>({ 0x58, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
+    0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66 });
+//pedersen commitment generator H: toPoint(cn_fast_hash(G))
+constexpr public_key H = bytes_to<public_key>({ 0x8b, 0x65, 0x59, 0x70, 0x15, 0x37, 0x99, 0xaf, 0x2a, 0xea, 0xdc, 0x9f, 0xf1,
+    0xad, 0xd0, 0xea, 0x6c, 0x72, 0x51, 0xd5, 0x41, 0x54, 0xcf, 0xa9, 0x2c, 0x17, 0x3a, 0x0d, 0xd3, 0x9c, 0x1f, 0x94 });
+static ge_p3 G_p3;
+static ge_p3 H_p3;
+static ge_cached G_cached;
+static ge_cached H_cached;
+
+// misc
+static std::once_flag init_gens_once_flag;
+
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+static public_key reproduce_generator_G()
+{
+    // G = {x, 4/5 mod q}
+    fe four, five, inv_five, y;
+    fe_0(four);
+    fe_0(five);
+    four[0] = 4;
+    five[0] = 5;
+    fe_invert(inv_five, five);
+    fe_mul(y, four, inv_five);
+
+    public_key reproduced_G;
+    fe_tobytes(to_bytes(reproduced_G), y);
+
+    return reproduced_G;
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+static public_key reproduce_generator_H()
+{
+    // H = 8*to_point(keccak(G))
+    // note: this does not use the point_from_bytes() function found in H_p(), instead directly interpreting the
+    //       input bytes as a compressed point (this can fail, so should not be used generically)
+    // note2: to_point(keccak(G)) is known to succeed for the canonical value of G (it will fail 7/8ths of the time
+    //        normally)
+    ge_p3 temp_p3;
+    ge_p2 temp_p2;
+    ge_p1p1 temp_p1p1;
+
+    hash H_temp_hash{cn_fast_hash(to_bytes(G), sizeof(ec_point))};
+    (void)H_temp_hash;  //suppress unused warning
+    assert(ge_frombytes_vartime(&temp_p3, reinterpret_cast<const unsigned char*>(&H_temp_hash)) == 0);
+    ge_p3_to_p2(&temp_p2, &temp_p3);
+    ge_mul8(&temp_p1p1, &temp_p2);
+    ge_p1p1_to_p3(&temp_p3, &temp_p1p1);
+
+    public_key reproduced_H;
+    ge_p3_tobytes(to_bytes(reproduced_H), &temp_p3);
+
+    return reproduced_H;
+}
+//-------------------------------------------------------------------------------------------------------------------
+// Make generators, but only once
+//-------------------------------------------------------------------------------------------------------------------
+static void init_gens()
+{
+    std::call_once(init_gens_once_flag,
+        [&](){
+
+        // sanity check the generators
+        static_assert(static_cast<unsigned char>(G.data[0]) == 0x58, "compile-time constant sanity check");
+        static_assert(static_cast<unsigned char>(H.data[0]) == 0x8b, "compile-time constant sanity check");
+
+        // build ge_p3 representations of generators
+        const int G_deserialize = ge_frombytes_vartime(&G_p3, to_bytes(G));
+        const int H_deserialize = ge_frombytes_vartime(&H_p3, to_bytes(H));
+
+        (void)G_deserialize; assert(G_deserialize == 0);
+        (void)H_deserialize; assert(H_deserialize == 0);
+
+        // get cached versions
+        ge_p3_to_cached(&G_cached, &G_p3);
+        ge_p3_to_cached(&H_cached, &H_p3);
+
+        // in debug mode, check that generators are reproducible
+        (void)reproduce_generator_G; assert(reproduce_generator_G() == G);
+        (void)reproduce_generator_H; assert(reproduce_generator_H() == H);
+
+    });
+}
+//-------------------------------------------------------------------------------------------------------------------
+public_key get_G()
+{
+    return G;
+}
+//-------------------------------------------------------------------------------------------------------------------
+public_key get_H()
+{
+    return H;
+}
+//-------------------------------------------------------------------------------------------------------------------
+ge_p3 get_G_p3()
+{
+    init_gens();
+    return G_p3;
+}
+//-------------------------------------------------------------------------------------------------------------------
+ge_p3 get_H_p3()
+{
+    init_gens();
+    return H_p3;
+}
+//-------------------------------------------------------------------------------------------------------------------
+ge_cached get_G_cached()
+{
+    init_gens();
+    return G_cached;
+}
+//-------------------------------------------------------------------------------------------------------------------
+ge_cached get_H_cached()
+{
+    init_gens();
+    return H_cached;
+}
+//-------------------------------------------------------------------------------------------------------------------
+} //namespace crypto

src/crypto/generators.h

@@ -0,0 +1,47 @@
+// Copyright (c) 2022, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+extern "C"
+{
+#include "crypto-ops.h"
+}
+#include "crypto.h"
+
+namespace crypto
+{
+
+public_key get_G();
+public_key get_H();
+ge_p3 get_G_p3();
+ge_p3 get_H_p3();
+ge_cached get_G_cached();
+ge_cached get_H_cached();
+
+} //namespace crypto

tests/unit_tests/crypto.cpp

@@ -32,8 +32,15 @@
 #include <sstream>
 #include <string>
 
+extern "C"
+{
+#include "crypto/crypto-ops.h"
+}
+#include "crypto/generators.h"
 #include "cryptonote_basic/cryptonote_basic_impl.h"
 #include "cryptonote_basic/merge_mining.h"
+#include "ringct/rctOps.h"
+#include "ringct/rctTypes.h"
 
 namespace
 {
@@ -312,3 +319,20 @@ TEST(Crypto, tree_branch)
     }
   }
 }
+
+TEST(Crypto, generator_consistency)
+{
+  // crypto/generators.h
+  const crypto::public_key G{crypto::get_G()};
+  const crypto::public_key H{crypto::get_H()};
+  const ge_p3 H_p3 = crypto::get_H_p3();
+
+  // crypto/crypto-ops.h
+  ASSERT_TRUE(memcmp(&H_p3, &ge_p3_H, sizeof(ge_p3)) == 0);
+
+  // ringct/rctOps.h
+  ASSERT_TRUE(memcmp(G.data, rct::G.bytes, 32) == 0);
+
+  // ringct/rctTypes.h
+  ASSERT_TRUE(memcmp(H.data, rct::H.bytes, 32) == 0);
+}