descriptors: disallow hybrid public keys

The descriptor documentation (doc/descriptors.md) and BIP380 explicitly
require that hex-encoded public keys start with 02 or 03 (compressed) or
04 (uncompressed). However, the current parsing/inference code permit 06
and 07 (hybrid) encoding as well. Fix this.

3 files changed, 21 insertions, 2 deletions

diff --git a/src/pubkey.h b/src/pubkey.h
index 274779f9a4..4b34fd829b 100644
--- a/src/pubkey.h
+++ b/src/pubkey.h
@@ -191,6 +191,12 @@ public:
         return size() > 0;
     }
 
+    /** Check if a public key is a syntactically valid compressed or uncompressed key. */
+    bool IsValidNonHybrid() const noexcept
+    {
+        return size() > 0 && (vch[0] == 0x02 || vch[0] == 0x03 || vch[0] == 0x04);
+    }
+
     //! fully validate whether this is a valid public key (more expensive than IsValid())
     bool IsFullyValid() const;
 
diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index 2f3f2c7a1d..896fb0b5b3 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -1290,6 +1290,10 @@ std::unique_ptr<PubkeyProvider> ParsePubkeyInner(uint32_t key_exp_index, const S
         if (IsHex(str)) {
             std::vector<unsigned char> data = ParseHex(str);
             CPubKey pubkey(data);
+            if (pubkey.IsValid() && !pubkey.IsValidNonHybrid()) {
+                error = "Hybrid public keys are not allowed";
+                return nullptr;
+            }
             if (pubkey.IsFullyValid()) {
                 if (permit_uncompressed || pubkey.IsCompressed()) {
                     return std::make_unique<ConstPubkeyProvider>(key_exp_index, pubkey, false);
@@ -1448,7 +1452,7 @@ struct KeyParser {
     {
         assert(m_in);
         CPubKey pubkey(begin, end);
-        if (pubkey.IsValid()) {
+        if (pubkey.IsValidNonHybrid()) {
             Key key = m_keys.size();
             m_keys.push_back(InferPubkey(pubkey, ParseScriptContext::P2WSH, *m_in));
             return key;
@@ -1795,7 +1799,7 @@ std::unique_ptr<DescriptorImpl> InferScript(const CScript& script, ParseScriptCo
 
     if (txntype == TxoutType::PUBKEY && (ctx == ParseScriptContext::TOP || ctx == ParseScriptContext::P2SH || ctx == ParseScriptContext::P2WSH)) {
         CPubKey pubkey(data[0]);
-        if (pubkey.IsValid()) {
+        if (pubkey.IsValidNonHybrid()) {
             return std::make_unique<PKDescriptor>(InferPubkey(pubkey, ctx, provider));
         }
     }
diff --git a/src/test/descriptor_tests.cpp b/src/test/descriptor_tests.cpp
index 3a30ef453e..60e441d457 100644
--- a/src/test/descriptor_tests.cpp
+++ b/src/test/descriptor_tests.cpp
@@ -409,6 +409,11 @@ BOOST_AUTO_TEST_CASE(descriptor_test)
     CheckUnparsable("wsh(pk(5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss))", "wsh(pk(04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235))", "pk(): Uncompressed keys are not allowed"); // No uncompressed keys in witness
     CheckUnparsable("sh(wpkh(5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss))", "sh(wpkh(04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235))", "wpkh(): Uncompressed keys are not allowed"); // No uncompressed keys in witness
 
+    // Equivalent single-key hybrid is not allowed
+    CheckUnparsable("", "combo(07a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)", "combo(): Hybrid public keys are not allowed");
+    CheckUnparsable("", "pk(0623542d61708e3fc48ba78fbe8fcc983ba94a520bc33f82b8e45e51dbc47af2726bcf181925eee1bdd868b109314f3ea92a6fc23d6b66057d3acfba04d6b08b58)", "pk(): Hybrid public keys are not allowed");
+    CheckUnparsable("", "pkh(07a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)", "pkh(): Hybrid public keys are not allowed");
+
     // Some unconventional single-key constructions
     Check("sh(pk(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1))", "sh(pk(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", "sh(pk(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", SIGNABLE, {{"a9141857af51a5e516552b3086430fd8ce55f7c1a52487"}}, OutputType::LEGACY);
     Check("sh(pkh(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1))", "sh(pkh(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", "sh(pkh(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", SIGNABLE, {{"a9141a31ad23bf49c247dd531a623c2ef57da3c400c587"}}, OutputType::LEGACY);
@@ -538,6 +543,10 @@ BOOST_AUTO_TEST_CASE(descriptor_test)
     CheckUnparsable("tr(and_v(vc:andor(pk(L4gM1FBdyHNpkzsFh9ipnofLhpZRp2mwobpeULy1a6dBTvw8Ywtd),pk_k(Kx9HCDjGiwFcgVNhTrS5z5NeZdD6veeam61eDxLDCkGWujvL4Gnn),and_v(v:older(1),pk_k(L4o2kDvXXDRH2VS9uBnouScLduWt4dZnM25se7kvEjJeQ285en2A))),after(10)))", "tr(and_v(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(02aa27e5eb2c185e87cd1dbc3e0efc9cb1175235e0259df1713424941c3cb40402))),after(10)))", "tr(): key 'and_v(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(02aa27e5eb2c185e87cd1dbc3e0efc9cb1175235e0259df1713424941c3cb40402))),after(10))' is not valid");
     CheckUnparsable("raw(and_v(vc:andor(pk(L4gM1FBdyHNpkzsFh9ipnofLhpZRp2mwobpeULy1a6dBTvw8Ywtd),pk_k(Kx9HCDjGiwFcgVNhTrS5z5NeZdD6veeam61eDxLDCkGWujvL4Gnn),and_v(v:older(1),pk_k(L4o2kDvXXDRH2VS9uBnouScLduWt4dZnM25se7kvEjJeQ285en2A))),after(10)))", "sh(and_v(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(02aa27e5eb2c185e87cd1dbc3e0efc9cb1175235e0259df1713424941c3cb40402))),after(10)))", "Miniscript expressions can only be used in wsh");
     CheckUnparsable("", "tr(034D2224bbbbbbbbbbcbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb40,{{{{{{{{{{{{{{{{{{{{{{multi(1,xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/967808'/9,xprvA1RpRA33e1JQ7ifknakTFNpgXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/968/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/3/4/5/58/55/2/5/58/58/2/5/5/5/8/5/2/8/5/85/2/8/2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/8/5/8/5/4/5/585/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/8/2/5/8/5/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/58/58/2/0/8/5/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/5/8/5/8/24/5/58/52/5/8/5/2/8/24/5/58/588/246/8/5/2/8/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/5/4/5/58/55/58/2/5/8/55/2/5/8/58/555/58/2/5/8/4//2/5/58/5w/2/5/8/5/2/4/5/58/5558'/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/8/2/5/8/5/5/8/58/2/5/58/58/2/5/8/9/588/2/58/2/5/8/5/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/82/5/8/5/5/58/52/6/8/5/2/8/{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}{{{{{{{{{DDD2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8588/246/8/5/2DLDDDDDDDbbD3DDDD/8/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/3/4/5/58/55/2/5/58/58/2/5/5/5/8/5/2/8/5/85/2/8/2/5/8D)/5/2/5/58/58/2/5/58/58/58/588/2/58/2/5/8/5/25/58/58/2/5/58/58/2/5/8/9/588/2/58/2/6780,xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFW/8/5/2/5/58678008')", "'multi(1,xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/967808'/9,xprvA1RpRA33e1JQ7ifknakTFNpgXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/968/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/3/4/5/58/55/2/5/58/58/2/5/5/5/8/5/2/8/5/85/2/8/2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/8/5/8/5/4/5/585/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/8/2/5/8/5/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/58/58/2/0/8/5/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/5/8/5/8/24/5/58/52/5/8/5/2/8/24/5/58/588/246/8/5/2/8/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/5/4/5/58/55/58/2/5/8/55/2/5/8/58/555/58/2/5/8/4//2/5/58/5w/2/5/8/5/2/4/5/58/5558'/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/8/2/5/8/5/5/8/58/2/5/58/58/2/5/8/9/588/2/58/2/5/8/5/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8/5/2/5/58/58/2/5/5/58/588/2/58/2/5/8/5/2/82/5/8/5/5/58/52/6/8/5/2/8/{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}{{{{{{{{{DDD2/5/8/5/2/5/58/58/2/5/58/58/588/2/58/2/8/5/8/5/4/5/58/588/2/6/8/5/2/8/2/5/8588/246/8/5/2DLDDDDDDDbbD3DDDD/8/2/5/8/5/2/5/58/58/2/5/5/5/58/588/2/6/8/5/2/8/2/5/8/2/58/2/5/8/5/2/8/5/8/3/4/5/58/55/2/5/58/58/2/5/5/5/8/5/2/8/5/85/2/8/2/5/8D)/5/2/5/58/58/2/5/58/58/58/588/2/58/2/5/8/5/25/58/58/2/5/58/58/2/5/8/9/588/2/58/2/6780,xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFW/8/5/2/5/58678008'' is not a valid descriptor function");
+    // No uncompressed keys allowed
+    CheckUnparsable("", "wsh(and_v(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(049228de6902abb4f541791f6d7f925b10e2078ccb1298856e5ea5cc5fd667f930eac37a00cc07f9a91ef3c2d17bf7a17db04552ff90ac312a5b8b4caca6c97aa4))),after(10)))", "A function is needed within P2WSH");
+    // No hybrid keys allowed
+    CheckUnparsable("", "wsh(and_v(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(069228de6902abb4f541791f6d7f925b10e2078ccb1298856e5ea5cc5fd667f930eac37a00cc07f9a91ef3c2d17bf7a17db04552ff90ac312a5b8b4caca6c97aa4))),after(10)))", "A function is needed within P2WSH");
     // Insane at top level
     CheckUnparsable("wsh(and_b(vc:andor(pk(L4gM1FBdyHNpkzsFh9ipnofLhpZRp2mwobpeULy1a6dBTvw8Ywtd),pk_k(Kx9HCDjGiwFcgVNhTrS5z5NeZdD6veeam61eDxLDCkGWujvL4Gnn),and_v(v:older(1),pk_k(L4o2kDvXXDRH2VS9uBnouScLduWt4dZnM25se7kvEjJeQ285en2A))),after(10)))", "wsh(and_b(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(02aa27e5eb2c185e87cd1dbc3e0efc9cb1175235e0259df1713424941c3cb40402))),after(10)))", "and_b(vc:andor(pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204),pk_k(032707170c71d8f75e4ca4e3fce870b9409dcaf12b051d3bcadff74747fa7619c0),and_v(v:older(1),pk_k(02aa27e5eb2c185e87cd1dbc3e0efc9cb1175235e0259df1713424941c3cb40402))),after(10)) is invalid");
     // Invalid sub