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MLSAG speedup and additional checks

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This commit is contained in:
Sarang Noether
2019-08-27 16:22:44 -04:00
parent 6335509727
commit 3a0451a8be
7 changed files with 75 additions and 101 deletions
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src/ringct/rctSigs.cpp
+40 -35
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@@ -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<geDsmp> 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<geDsmp> 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);
}