From 3a0451a8be43154f0da06dd9c693ed6f0c657042 Mon Sep 17 00:00:00 2001 From: Sarang Noether <32460187+SarangNoether@users.noreply.github.com> Date: Tue, 27 Aug 2019 16:22:44 -0400 Subject: MLSAG speedup and additional checks --- src/ringct/rctSigs.cpp | 75 +++++++++++++++++++++++++++----------------------- 1 file changed, 40 insertions(+), 35 deletions(-) (limited to 'src/ringct/rctSigs.cpp') diff --git a/src/ringct/rctSigs.cpp b/src/ringct/rctSigs.cpp index ff2a81d43..a7b265d63 100644 --- a/src/ringct/rctSigs.cpp +++ b/src/ringct/rctSigs.cpp @@ -163,14 +163,11 @@ namespace rct { return verifyBorromean(bb, P1_p3, P2_p3); } - //Multilayered Spontaneous Anonymous Group Signatures (MLSAG signatures) - //This is a just slghtly more efficient version than the ones described below - //(will be explained in more detail in Ring Multisig paper - //These are aka MG signatutes in earlier drafts of the ring ct paper - // c.f. https://eprint.iacr.org/2015/1098 section 2. - // Gen creates a signature which proves that for some column in the keymatrix "pk" - // the signer knows a secret key for each row in that column - // Ver verifies that the MG sig was created correctly + // MLSAG signatures + // See paper by Noether (https://eprint.iacr.org/2015/1098) + // This generalization allows for some dimensions not to require linkability; + // this is used in practice for commitment data within signatures + // Note that using more than one linkable dimension is not recommended. mgSig MLSAG_Gen(const key &message, const keyM & pk, const keyV & xx, const multisig_kLRki *kLRki, key *mscout, const unsigned int index, size_t dsRows, hw::device &hwdev) { mgSig rv; size_t cols = pk.size(); @@ -188,6 +185,7 @@ namespace rct { size_t i = 0, j = 0, ii = 0; key c, c_old, L, R, Hi; + ge_p3 Hi_p3; sc_0(c_old.bytes); vector Ip(dsRows); rv.II = keyV(dsRows); @@ -208,7 +206,8 @@ namespace rct { rv.II[i] = kLRki->ki; } else { - Hi = hashToPoint(pk[index][i]); + hash_to_p3(Hi_p3, pk[index][i]); + ge_p3_tobytes(Hi.bytes, &Hi_p3); hwdev.mlsag_prepare(Hi, xx[i], alpha[i] , aG[i] , aHP[i] , rv.II[i]); toHash[3 * i + 2] = aG[i]; toHash[3 * i + 3] = aHP[i]; @@ -235,7 +234,8 @@ namespace rct { sc_0(c.bytes); for (j = 0; j < dsRows; j++) { addKeys2(L, rv.ss[i][j], c_old, pk[i][j]); - hashToPoint(Hi, pk[i][j]); + hash_to_p3(Hi_p3, pk[i][j]); + ge_p3_tobytes(Hi.bytes, &Hi_p3); addKeys3(R, rv.ss[i][j], Hi, c_old, Ip[j].k); toHash[3 * j + 1] = pk[i][j]; toHash[3 * j + 2] = L; @@ -260,43 +260,42 @@ namespace rct { return rv; } - //Multilayered Spontaneous Anonymous Group Signatures (MLSAG signatures) - //This is a just slghtly more efficient version than the ones described below - //(will be explained in more detail in Ring Multisig paper - //These are aka MG signatutes in earlier drafts of the ring ct paper - // c.f. https://eprint.iacr.org/2015/1098 section 2. - // Gen creates a signature which proves that for some column in the keymatrix "pk" - // the signer knows a secret key for each row in that column - // Ver verifies that the MG sig was created correctly + // MLSAG signatures + // See paper by Noether (https://eprint.iacr.org/2015/1098) + // This generalization allows for some dimensions not to require linkability; + // this is used in practice for commitment data within signatures + // Note that using more than one linkable dimension is not recommended. bool MLSAG_Ver(const key &message, const keyM & pk, const mgSig & rv, size_t dsRows) { - size_t cols = pk.size(); - CHECK_AND_ASSERT_MES(cols >= 2, false, "Error! What is c if cols = 1!"); + CHECK_AND_ASSERT_MES(cols >= 2, false, "Signature must contain more than one public key"); size_t rows = pk[0].size(); - CHECK_AND_ASSERT_MES(rows >= 1, false, "Empty pk"); + CHECK_AND_ASSERT_MES(rows >= 1, false, "Bad total row number"); for (size_t i = 1; i < cols; ++i) { - CHECK_AND_ASSERT_MES(pk[i].size() == rows, false, "pk is not rectangular"); + CHECK_AND_ASSERT_MES(pk[i].size() == rows, false, "Bad public key matrix dimensions"); } - CHECK_AND_ASSERT_MES(rv.II.size() == dsRows, false, "Bad II size"); - CHECK_AND_ASSERT_MES(rv.ss.size() == cols, false, "Bad rv.ss size"); + CHECK_AND_ASSERT_MES(rv.II.size() == dsRows, false, "Wrong number of key images present"); + CHECK_AND_ASSERT_MES(rv.ss.size() == cols, false, "Bad scalar matrix dimensions"); for (size_t i = 0; i < cols; ++i) { - CHECK_AND_ASSERT_MES(rv.ss[i].size() == rows, false, "rv.ss is not rectangular"); + CHECK_AND_ASSERT_MES(rv.ss[i].size() == rows, false, "Bad scalar matrix dimensions"); } - CHECK_AND_ASSERT_MES(dsRows <= rows, false, "Bad dsRows value"); + CHECK_AND_ASSERT_MES(dsRows <= rows, false, "Non-double-spend rows cannot exceed total rows"); - for (size_t i = 0; i < rv.ss.size(); ++i) - for (size_t j = 0; j < rv.ss[i].size(); ++j) - CHECK_AND_ASSERT_MES(sc_check(rv.ss[i][j].bytes) == 0, false, "Bad ss slot"); - CHECK_AND_ASSERT_MES(sc_check(rv.cc.bytes) == 0, false, "Bad cc"); + for (size_t i = 0; i < rv.ss.size(); ++i) { + for (size_t j = 0; j < rv.ss[i].size(); ++j) { + CHECK_AND_ASSERT_MES(sc_check(rv.ss[i][j].bytes) == 0, false, "Bad signature scalar"); + } + } + CHECK_AND_ASSERT_MES(sc_check(rv.cc.bytes) == 0, false, "Bad initial signature hash"); size_t i = 0, j = 0, ii = 0; - key c, L, R, Hi; + key c, L, R; key c_old = copy(rv.cc); vector Ip(dsRows); for (i = 0 ; i < dsRows ; i++) { + CHECK_AND_ASSERT_MES(!(rv.II[i] == rct::identity()), false, "Bad key image"); precomp(Ip[i].k, rv.II[i]); } - size_t ndsRows = 3 * dsRows; //non Double Spendable Rows (see identity chains paper + size_t ndsRows = 3 * dsRows; // number of dimensions not requiring linkability keyV toHash(1 + 3 * dsRows + 2 * (rows - dsRows)); toHash[0] = message; i = 0; @@ -304,9 +303,14 @@ namespace rct { sc_0(c.bytes); for (j = 0; j < dsRows; j++) { addKeys2(L, rv.ss[i][j], c_old, pk[i][j]); - hashToPoint(Hi, pk[i][j]); - CHECK_AND_ASSERT_MES(!(Hi == rct::identity()), false, "Data hashed to point at infinity"); - addKeys3(R, rv.ss[i][j], Hi, c_old, Ip[j].k); + + // Compute R directly + ge_p3 hash8_p3; + hash_to_p3(hash8_p3, pk[i][j]); + ge_p2 R_p2; + ge_double_scalarmult_precomp_vartime(&R_p2, rv.ss[i][j].bytes, &hash8_p3, c_old.bytes, Ip[j].k); + ge_tobytes(R.bytes, &R_p2); + toHash[3 * j + 1] = pk[i][j]; toHash[3 * j + 2] = L; toHash[3 * j + 3] = R; @@ -317,6 +321,7 @@ namespace rct { toHash[ndsRows + 2 * ii + 2] = L; } c = hash_to_scalar(toHash); + CHECK_AND_ASSERT_MES(!(c == rct::zero()), false, "Bad signature hash"); copy(c_old, c); i = (i + 1); } -- cgit v1.2.3