Make empty byte arrays pass CheckSignatureEncoding()
Makes it possible to compactly provide a delibrately invalid signature for use with CHECK(MULTI)SIG. For instance with BIP19 if m != n invalid signatures need to be provided in the scriptSig; prior to this change those invalid signatures would need to be large DER-encoded signatures. Note that we may want to further expand on this change in the future by saying that only OP_0 is a "valid" invalid signature; BIP19 even with this change is inherently malleable as the invalid signatures can be any validly encoded DER signature.
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4 changed files with 11 additions and 5 deletions
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@ -189,6 +189,11 @@ bool static IsDefinedHashtypeSignature(const valtype &vchSig) {
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}
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bool static CheckSignatureEncoding(const valtype &vchSig, unsigned int flags, ScriptError* serror) {
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// Empty signature. Not strictly DER encoded, but allowed to provide a
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// compact way to provide an invalid signature for use with CHECK(MULTI)SIG
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if (vchSig.size() == 0) {
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return true;
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}
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if ((flags & (SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC)) != 0 && !IsDERSignature(vchSig)) {
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return set_error(serror, SCRIPT_ERR_SIG_DER);
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} else if ((flags & SCRIPT_VERIFY_LOW_S) != 0 && !IsLowDERSignature(vchSig, serror)) {
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@ -504,7 +504,7 @@
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"2-of-2 CHECKMULTISIG NOT with the first pubkey invalid, and both signatures validly encoded."
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],
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[
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"0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501 0",
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"0 0x47 0x3044022044dc17b0887c161bb67ba9635bf758735bdde503e4b0a0987f587f14a4e1143d022009a215772d49a85dae40d8ca03955af26ad3978a0ff965faa12915e9586249a501 1",
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"2 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 2 CHECKMULTISIG NOT",
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"STRICTENC",
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"2-of-2 CHECKMULTISIG NOT with both pubkeys valid, but first signature invalid."
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@ -662,6 +662,11 @@
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["0 0 0x02 0x0000", "CHECKMULTISIGVERIFY 1", ""],
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["0 0x02 0x0000 0", "CHECKMULTISIGVERIFY 1", ""],
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["While not really correctly DER encoded, the empty signature is allowed by"],
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["STRICTENC to provide a compact way to provide a delibrately invalid signature."],
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["0", "0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 CHECKSIG NOT", "STRICTENC"],
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["0 0", "1 0x21 0x02865c40293a680cb9c020e7b1e106d8c1916d3cef99aa431a56d253e69256dac0 1 CHECKMULTISIG NOT", "STRICTENC"],
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["CHECKMULTISIG evaluation order tests. CHECKMULTISIG evaluates signatures and"],
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["pubkeys in a specific order, and will exit early if the number of signatures"],
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["left to check is greater than the number of keys left. As STRICTENC fails the"],
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@ -116,10 +116,6 @@ BOOST_AUTO_TEST_CASE(multisig_verify)
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}
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}
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s.clear();
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s << OP_0 << OP_0;
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BOOST_CHECK(!VerifyScript(s, a_or_b, flags, SignatureChecker(txTo[1], 0), &err));
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BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_SIG_DER, ScriptErrorString(err));
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s.clear();
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s << OP_0 << OP_1;
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BOOST_CHECK(!VerifyScript(s, a_or_b, flags, SignatureChecker(txTo[1], 0), &err));
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BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_SIG_DER, ScriptErrorString(err));
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