Miniscript: conversion from script

Co-Authored-By: Antoine Poinsot <darosior@protonmail.com>
Co-Authored-By: Samuel Dobson <dobsonsa68@gmail.com>

3 files changed, 534 insertions, 0 deletions

diff --git a/src/script/miniscript.cpp b/src/script/miniscript.cpp
index 8074be6cde..d0bb937885 100644
--- a/src/script/miniscript.cpp
+++ b/src/script/miniscript.cpp
@@ -5,6 +5,7 @@
 #include <string>
 #include <vector>
 #include <script/script.h>
+#include <script/standard.h>
 #include <script/miniscript.h>
 
 #include <assert.h>
@@ -281,6 +282,58 @@ size_t ComputeScriptLen(Fragment nodetype, Type sub0typ, size_t subsize, uint32_
     return 0;
 }
 
+bool DecomposeScript(const CScript& script, std::vector<std::pair<opcodetype, std::vector<unsigned char>>>& out)
+{
+    out.clear();
+    CScript::const_iterator it = script.begin(), itend = script.end();
+    while (it != itend) {
+        std::vector<unsigned char> push_data;
+        opcodetype opcode;
+        if (!script.GetOp(it, opcode, push_data)) {
+            out.clear();
+            return false;
+        } else if (opcode >= OP_1 && opcode <= OP_16) {
+            // Deal with OP_n (GetOp does not turn them into pushes).
+            push_data.assign(1, CScript::DecodeOP_N(opcode));
+        } else if (opcode == OP_CHECKSIGVERIFY) {
+            // Decompose OP_CHECKSIGVERIFY into OP_CHECKSIG OP_VERIFY
+            out.emplace_back(OP_CHECKSIG, std::vector<unsigned char>());
+            opcode = OP_VERIFY;
+        } else if (opcode == OP_CHECKMULTISIGVERIFY) {
+            // Decompose OP_CHECKMULTISIGVERIFY into OP_CHECKMULTISIG OP_VERIFY
+            out.emplace_back(OP_CHECKMULTISIG, std::vector<unsigned char>());
+            opcode = OP_VERIFY;
+        } else if (opcode == OP_EQUALVERIFY) {
+            // Decompose OP_EQUALVERIFY into OP_EQUAL OP_VERIFY
+            out.emplace_back(OP_EQUAL, std::vector<unsigned char>());
+            opcode = OP_VERIFY;
+        } else if (IsPushdataOp(opcode)) {
+            if (!CheckMinimalPush(push_data, opcode)) return false;
+        } else if (it != itend && (opcode == OP_CHECKSIG || opcode == OP_CHECKMULTISIG || opcode == OP_EQUAL) && (*it == OP_VERIFY)) {
+            // Rule out non minimal VERIFY sequences
+            return false;
+        }
+        out.emplace_back(opcode, std::move(push_data));
+    }
+    std::reverse(out.begin(), out.end());
+    return true;
+}
+
+bool ParseScriptNumber(const std::pair<opcodetype, std::vector<unsigned char>>& in, int64_t& k) {
+    if (in.first == OP_0) {
+        k = 0;
+        return true;
+    }
+    if (!in.second.empty()) {
+        if (IsPushdataOp(in.first) && !CheckMinimalPush(in.second, in.first)) return false;
+        try {
+            k = CScriptNum(in.second, true).GetInt64();
+            return true;
+        } catch(const scriptnum_error&) {}
+    }
+    return false;
+}
+
 int FindNextChar(Span<const char> sp, const char m)
 {
     for (int i = 0; i < (int)sp.size(); ++i) {
diff --git a/src/script/miniscript.h b/src/script/miniscript.h
index a394aed146..2ff6b02561 100644
--- a/src/script/miniscript.h
+++ b/src/script/miniscript.h
@@ -220,6 +220,7 @@ enum class Fragment {
     // WRAP_U(X) is represented as OR_I(X,0)
 };
 
+
 namespace internal {
 
 //! Helper function for Node::CalcType.
@@ -1008,6 +1009,442 @@ inline NodeRef<Key> Parse(Span<const char> in, const Ctx& ctx)
     return tl_node;
 }
 
+/** Decode a script into opcode/push pairs.
+ *
+ * Construct a vector with one element per opcode in the script, in reverse order.
+ * Each element is a pair consisting of the opcode, as well as the data pushed by
+ * the opcode (including OP_n), if any. OP_CHECKSIGVERIFY, OP_CHECKMULTISIGVERIFY,
+ * and OP_EQUALVERIFY are decomposed into OP_CHECKSIG, OP_CHECKMULTISIG, OP_EQUAL
+ * respectively, plus OP_VERIFY.
+ */
+bool DecomposeScript(const CScript& script, std::vector<std::pair<opcodetype, std::vector<unsigned char>>>& out);
+
+/** Determine whether the passed pair (created by DecomposeScript) is pushing a number. */
+bool ParseScriptNumber(const std::pair<opcodetype, std::vector<unsigned char>>& in, int64_t& k);
+
+enum class DecodeContext {
+    /** A single expression of type B, K, or V. Specifically, this can't be an
+     * and_v or an expression of type W (a: and s: wrappers). */
+    SINGLE_BKV_EXPR,
+    /** Potentially multiple SINGLE_BKV_EXPRs as children of (potentially multiple)
+     * and_v expressions. Syntactic sugar for MAYBE_AND_V + SINGLE_BKV_EXPR. */
+    BKV_EXPR,
+    /** An expression of type W (a: or s: wrappers). */
+    W_EXPR,
+
+    /** SWAP expects the next element to be OP_SWAP (inside a W-type expression that
+     * didn't end with FROMALTSTACK), and wraps the top of the constructed stack
+     * with s: */
+    SWAP,
+    /** ALT expects the next element to be TOALTSTACK (we must have already read a
+     * FROMALTSTACK earlier), and wraps the top of the constructed stack with a: */
+    ALT,
+    /** CHECK wraps the top constructed node with c: */
+    CHECK,
+    /** DUP_IF wraps the top constructed node with d: */
+    DUP_IF,
+    /** VERIFY wraps the top constructed node with v: */
+    VERIFY,
+    /** NON_ZERO wraps the top constructed node with j: */
+    NON_ZERO,
+    /** ZERO_NOTEQUAL wraps the top constructed node with n: */
+    ZERO_NOTEQUAL,
+
+    /** MAYBE_AND_V will check if the next part of the script could be a valid
+     * miniscript sub-expression, and if so it will push AND_V and SINGLE_BKV_EXPR
+     * to decode it and construct the and_v node. This is recursive, to deal with
+     * multiple and_v nodes inside each other. */
+    MAYBE_AND_V,
+    /** AND_V will construct an and_v node from the last two constructed nodes. */
+    AND_V,
+    /** AND_B will construct an and_b node from the last two constructed nodes. */
+    AND_B,
+    /** ANDOR will construct an andor node from the last three constructed nodes. */
+    ANDOR,
+    /** OR_B will construct an or_b node from the last two constructed nodes. */
+    OR_B,
+    /** OR_C will construct an or_c node from the last two constructed nodes. */
+    OR_C,
+    /** OR_D will construct an or_d node from the last two constructed nodes. */
+    OR_D,
+
+    /** In a thresh expression, all sub-expressions other than the first are W-type,
+     * and end in OP_ADD. THRESH_W will check for this OP_ADD and either push a W_EXPR
+     * or a SINGLE_BKV_EXPR and jump to THRESH_E accordingly. */
+    THRESH_W,
+    /** THRESH_E constructs a thresh node from the appropriate number of constructed
+     * children. */
+    THRESH_E,
+
+    /** ENDIF signals that we are inside some sort of OP_IF structure, which could be
+     * or_d, or_c, or_i, andor, d:, or j: wrapper, depending on what follows. We read
+     * a BKV_EXPR and then deal with the next opcode case-by-case. */
+    ENDIF,
+    /** If, inside an ENDIF context, we find an OP_NOTIF before finding an OP_ELSE,
+     * we could either be in an or_d or an or_c node. We then check for IFDUP to
+     * distinguish these cases. */
+    ENDIF_NOTIF,
+    /** If, inside an ENDIF context, we find an OP_ELSE, then we could be in either an
+     * or_i or an andor node. Read the next BKV_EXPR and find either an OP_IF or an
+     * OP_NOTIF. */
+    ENDIF_ELSE,
+};
+
+//! Parse a miniscript from a bitcoin script
+template<typename Key, typename Ctx, typename I>
+inline NodeRef<Key> DecodeScript(I& in, I last, const Ctx& ctx)
+{
+    // The two integers are used to hold state for thresh()
+    std::vector<std::tuple<DecodeContext, int64_t, int64_t>> to_parse;
+    std::vector<NodeRef<Key>> constructed;
+
+    // This is the top level, so we assume the type is B
+    // (in particular, disallowing top level W expressions)
+    to_parse.emplace_back(DecodeContext::BKV_EXPR, -1, -1);
+
+    while (!to_parse.empty()) {
+        // Exit early if the Miniscript is not going to be valid.
+        if (!constructed.empty() && !constructed.back()->IsValid()) return {};
+
+        // Get the current context we are decoding within
+        auto [cur_context, n, k] = to_parse.back();
+        to_parse.pop_back();
+
+        switch(cur_context) {
+        case DecodeContext::SINGLE_BKV_EXPR: {
+            if (in >= last) return {};
+
+            // Constants
+            if (in[0].first == OP_1) {
+                ++in;
+                constructed.push_back(MakeNodeRef<Key>(Fragment::JUST_1));
+                break;
+            }
+            if (in[0].first == OP_0) {
+                ++in;
+                constructed.push_back(MakeNodeRef<Key>(Fragment::JUST_0));
+                break;
+            }
+            // Public keys
+            if (in[0].second.size() == 33) {
+                Key key;
+                if (!ctx.FromPKBytes(in[0].second.begin(), in[0].second.end(), key)) return {};
+                ++in;
+                constructed.push_back(MakeNodeRef<Key>(Fragment::PK_K, Vector(std::move(key))));
+                break;
+            }
+            if (last - in >= 5 && in[0].first == OP_VERIFY && in[1].first == OP_EQUAL && in[3].first == OP_HASH160 && in[4].first == OP_DUP && in[2].second.size() == 20) {
+                Key key;
+                if (!ctx.FromPKHBytes(in[2].second.begin(), in[2].second.end(), key)) return {};
+                in += 5;
+                constructed.push_back(MakeNodeRef<Key>(Fragment::PK_H, Vector(std::move(key))));
+                break;
+            }
+            // Time locks
+            if (last - in >= 2 && in[0].first == OP_CHECKSEQUENCEVERIFY && ParseScriptNumber(in[1], k)) {
+                in += 2;
+                if (k < 1 || k > 0x7FFFFFFFL) return {};
+                constructed.push_back(MakeNodeRef<Key>(Fragment::OLDER, k));
+                break;
+            }
+            if (last - in >= 2 && in[0].first == OP_CHECKLOCKTIMEVERIFY && ParseScriptNumber(in[1], k)) {
+                in += 2;
+                if (k < 1 || k > 0x7FFFFFFFL) return {};
+                constructed.push_back(MakeNodeRef<Key>(Fragment::AFTER, k));
+                break;
+            }
+            // Hashes
+            if (last - in >= 7 && in[0].first == OP_EQUAL && in[3].first == OP_VERIFY && in[4].first == OP_EQUAL && ParseScriptNumber(in[5], k) && k == 32 && in[6].first == OP_SIZE) {
+                if (in[2].first == OP_SHA256 && in[1].second.size() == 32) {
+                    constructed.push_back(MakeNodeRef<Key>(Fragment::SHA256, in[1].second));
+                    in += 7;
+                    break;
+                } else if (in[2].first == OP_RIPEMD160 && in[1].second.size() == 20) {
+                    constructed.push_back(MakeNodeRef<Key>(Fragment::RIPEMD160, in[1].second));
+                    in += 7;
+                    break;
+                } else if (in[2].first == OP_HASH256 && in[1].second.size() == 32) {
+                    constructed.push_back(MakeNodeRef<Key>(Fragment::HASH256, in[1].second));
+                    in += 7;
+                    break;
+                } else if (in[2].first == OP_HASH160 && in[1].second.size() == 20) {
+                    constructed.push_back(MakeNodeRef<Key>(Fragment::HASH160, in[1].second));
+                    in += 7;
+                    break;
+                }
+            }
+            // Multi
+            if (last - in >= 3 && in[0].first == OP_CHECKMULTISIG) {
+                std::vector<Key> keys;
+                if (!ParseScriptNumber(in[1], n)) return {};
+                if (last - in < 3 + n) return {};
+                if (n < 1 || n > 20) return {};
+                for (int i = 0; i < n; ++i) {
+                    Key key;
+                    if (in[2 + i].second.size() != 33) return {};
+                    if (!ctx.FromPKBytes(in[2 + i].second.begin(), in[2 + i].second.end(), key)) return {};
+                    keys.push_back(std::move(key));
+                }
+                if (!ParseScriptNumber(in[2 + n], k)) return {};
+                if (k < 1 || k > n) return {};
+                in += 3 + n;
+                std::reverse(keys.begin(), keys.end());
+                constructed.push_back(MakeNodeRef<Key>(Fragment::MULTI, std::move(keys), k));
+                break;
+            }
+            /** In the following wrappers, we only need to push SINGLE_BKV_EXPR rather
+             * than BKV_EXPR, because and_v commutes with these wrappers. For example,
+             * c:and_v(X,Y) produces the same script as and_v(X,c:Y). */
+            // c: wrapper
+            if (in[0].first == OP_CHECKSIG) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::CHECK, -1, -1);
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+                break;
+            }
+            // v: wrapper
+            if (in[0].first == OP_VERIFY) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::VERIFY, -1, -1);
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+                break;
+            }
+            // n: wrapper
+            if (in[0].first == OP_0NOTEQUAL) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ZERO_NOTEQUAL, -1, -1);
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+                break;
+            }
+            // Thresh
+            if (last - in >= 3 && in[0].first == OP_EQUAL && ParseScriptNumber(in[1], k)) {
+                if (k < 1) return {};
+                in += 2;
+                to_parse.emplace_back(DecodeContext::THRESH_W, 0, k);
+                break;
+            }
+            // OP_ENDIF can be WRAP_J, WRAP_D, ANDOR, OR_C, OR_D, or OR_I
+            if (in[0].first == OP_ENDIF) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ENDIF, -1, -1);
+                to_parse.emplace_back(DecodeContext::BKV_EXPR, -1, -1);
+                break;
+            }
+            /** In and_b and or_b nodes, we only look for SINGLE_BKV_EXPR, because
+             * or_b(and_v(X,Y),Z) has script [X] [Y] [Z] OP_BOOLOR, the same as
+             * and_v(X,or_b(Y,Z)). In this example, the former of these is invalid as
+             * miniscript, while the latter is valid. So we leave the and_v "outside"
+             * while decoding. */
+            // and_b
+            if (in[0].first == OP_BOOLAND) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::AND_B, -1, -1);
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+                to_parse.emplace_back(DecodeContext::W_EXPR, -1, -1);
+                break;
+            }
+            // or_b
+            if (in[0].first == OP_BOOLOR) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::OR_B, -1, -1);
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+                to_parse.emplace_back(DecodeContext::W_EXPR, -1, -1);
+                break;
+            }
+            // Unrecognised expression
+            return {};
+        }
+        case DecodeContext::BKV_EXPR: {
+            to_parse.emplace_back(DecodeContext::MAYBE_AND_V, -1, -1);
+            to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+            break;
+        }
+        case DecodeContext::W_EXPR: {
+            // a: wrapper
+            if (in >= last) return {};
+            if (in[0].first == OP_FROMALTSTACK) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ALT, -1, -1);
+            } else {
+                to_parse.emplace_back(DecodeContext::SWAP, -1, -1);
+            }
+            to_parse.emplace_back(DecodeContext::BKV_EXPR, -1, -1);
+            break;
+        }
+        case DecodeContext::MAYBE_AND_V: {
+            // If we reach a potential AND_V top-level, check if the next part of the script could be another AND_V child
+            // These op-codes cannot end any well-formed miniscript so cannot be used in an and_v node.
+            if (in < last && in[0].first != OP_IF && in[0].first != OP_ELSE && in[0].first != OP_NOTIF && in[0].first != OP_TOALTSTACK && in[0].first != OP_SWAP) {
+                to_parse.emplace_back(DecodeContext::AND_V, -1, -1);
+                // BKV_EXPR can contain more AND_V nodes
+                to_parse.emplace_back(DecodeContext::BKV_EXPR, -1, -1);
+            }
+            break;
+        }
+        case DecodeContext::SWAP: {
+            if (in >= last || in[0].first != OP_SWAP || constructed.empty()) return {};
+            ++in;
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_S, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::ALT: {
+            if (in >= last || in[0].first != OP_TOALTSTACK || constructed.empty()) return {};
+            ++in;
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_A, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::CHECK: {
+            if (constructed.empty()) return {};
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_C, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::DUP_IF: {
+            if (constructed.empty()) return {};
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_D, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::VERIFY: {
+            if (constructed.empty()) return {};
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_V, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::NON_ZERO: {
+            if (constructed.empty()) return {};
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_J, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::ZERO_NOTEQUAL: {
+            if (constructed.empty()) return {};
+            constructed.back() = MakeNodeRef<Key>(Fragment::WRAP_N, Vector(std::move(constructed.back())));
+            break;
+        }
+        case DecodeContext::AND_V: {
+            if (constructed.size() < 2) return {};
+            BuildBack(Fragment::AND_V, constructed, /* reverse */ true);
+            break;
+        }
+        case DecodeContext::AND_B: {
+            if (constructed.size() < 2) return {};
+            BuildBack(Fragment::AND_B, constructed, /* reverse */ true);
+            break;
+        }
+        case DecodeContext::OR_B: {
+            if (constructed.size() < 2) return {};
+            BuildBack(Fragment::OR_B, constructed, /* reverse */ true);
+            break;
+        }
+        case DecodeContext::OR_C: {
+            if (constructed.size() < 2) return {};
+            BuildBack(Fragment::OR_C, constructed, /* reverse */ true);
+            break;
+        }
+        case DecodeContext::OR_D: {
+            if (constructed.size() < 2) return {};
+            BuildBack(Fragment::OR_D, constructed, /* reverse */ true);
+            break;
+        }
+        case DecodeContext::ANDOR: {
+            if (constructed.size() < 3) return {};
+            NodeRef<Key> left = std::move(constructed.back());
+            constructed.pop_back();
+            NodeRef<Key> right = std::move(constructed.back());
+            constructed.pop_back();
+            NodeRef<Key> mid = std::move(constructed.back());
+            constructed.back() = MakeNodeRef<Key>(Fragment::ANDOR, Vector(std::move(left), std::move(mid), std::move(right)));
+            break;
+        }
+        case DecodeContext::THRESH_W: {
+            if (in >= last) return {};
+            if (in[0].first == OP_ADD) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::THRESH_W, n+1, k);
+                to_parse.emplace_back(DecodeContext::W_EXPR, -1, -1);
+            } else {
+                to_parse.emplace_back(DecodeContext::THRESH_E, n+1, k);
+                // All children of thresh have type modifier d, so cannot be and_v
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+            }
+            break;
+        }
+        case DecodeContext::THRESH_E: {
+            if (k < 1 || k > n || constructed.size() < static_cast<size_t>(n)) return {};
+            std::vector<NodeRef<Key>> subs;
+            for (int i = 0; i < n; ++i) {
+                NodeRef<Key> sub = std::move(constructed.back());
+                constructed.pop_back();
+                subs.push_back(std::move(sub));
+            }
+            constructed.push_back(MakeNodeRef<Key>(Fragment::THRESH, std::move(subs), k));
+            break;
+        }
+        case DecodeContext::ENDIF: {
+            if (in >= last) return {};
+
+            // could be andor or or_i
+            if (in[0].first == OP_ELSE) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ENDIF_ELSE, -1, -1);
+                to_parse.emplace_back(DecodeContext::BKV_EXPR, -1, -1);
+            }
+            // could be j: or d: wrapper
+            else if (in[0].first == OP_IF) {
+                if (last - in >= 2 && in[1].first == OP_DUP) {
+                    in += 2;
+                    to_parse.emplace_back(DecodeContext::DUP_IF, -1, -1);
+                } else if (last - in >= 3 && in[1].first == OP_0NOTEQUAL && in[2].first == OP_SIZE) {
+                    in += 3;
+                    to_parse.emplace_back(DecodeContext::NON_ZERO, -1, -1);
+                }
+                else {
+                    return {};
+                }
+            // could be or_c or or_d
+            } else if (in[0].first == OP_NOTIF) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ENDIF_NOTIF, -1, -1);
+            }
+            else {
+                return {};
+            }
+            break;
+        }
+        case DecodeContext::ENDIF_NOTIF: {
+            if (in >= last) return {};
+            if (in[0].first == OP_IFDUP) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::OR_D, -1, -1);
+            } else {
+                to_parse.emplace_back(DecodeContext::OR_C, -1, -1);
+            }
+            // or_c and or_d both require X to have type modifier d so, can't contain and_v
+            to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+            break;
+        }
+        case DecodeContext::ENDIF_ELSE: {
+            if (in >= last) return {};
+            if (in[0].first == OP_IF) {
+                ++in;
+                BuildBack(Fragment::OR_I, constructed, /* reverse */ true);
+            } else if (in[0].first == OP_NOTIF) {
+                ++in;
+                to_parse.emplace_back(DecodeContext::ANDOR, -1, -1);
+                // andor requires X to have type modifier d, so it can't be and_v
+                to_parse.emplace_back(DecodeContext::SINGLE_BKV_EXPR, -1, -1);
+            } else {
+                return {};
+            }
+            break;
+        }
+        }
+    }
+    if (constructed.size() != 1) return {};
+    const NodeRef<Key> tl_node = std::move(constructed.front());
+    // Note that due to how ComputeType works (only assign the type to the node if the
+    // subs' types are valid) this would fail if any node of tree is badly typed.
+    if (!tl_node->IsValidTopLevel()) return {};
+    return tl_node;
+}
+
 } // namespace internal
 
 template<typename Ctx>
@@ -1015,6 +1452,18 @@ inline NodeRef<typename Ctx::Key> FromString(const std::string& str, const Ctx&
     return internal::Parse<typename Ctx::Key>(str, ctx);
 }
 
+template<typename Ctx>
+inline NodeRef<typename Ctx::Key> FromScript(const CScript& script, const Ctx& ctx) {
+    using namespace internal;
+    std::vector<std::pair<opcodetype, std::vector<unsigned char>>> decomposed;
+    if (!DecomposeScript(script, decomposed)) return {};
+    auto it = decomposed.begin();
+    auto ret = DecodeScript<typename Ctx::Key>(it, decomposed.end(), ctx);
+    if (!ret) return {};
+    if (it != decomposed.end()) return {};
+    return ret;
+}
+
 } // namespace miniscript
 
 #endif // BITCOIN_SCRIPT_MINISCRIPT_H
diff --git a/src/test/miniscript_tests.cpp b/src/test/miniscript_tests.cpp
index 752a20d155..5950c81561 100644
--- a/src/test/miniscript_tests.cpp
+++ b/src/test/miniscript_tests.cpp
@@ -23,6 +23,7 @@ struct TestData {
     std::vector<CPubKey> pubkeys;
     //! A map from the public keys to their CKeyIDs (faster than hashing every time).
     std::map<CPubKey, CKeyID> pkhashes;
+    std::map<CKeyID, CPubKey> pkmap;
 
     // Various precomputed hashes
     std::vector<std::vector<unsigned char>> sha256;
@@ -45,6 +46,7 @@ struct TestData {
             CKeyID keyid = pubkey.GetID();
             pubkeys.push_back(pubkey);
             pkhashes.emplace(pubkey, keyid);
+            pkmap.emplace(keyid, pubkey);
 
             // Compute various hashes
             std::vector<unsigned char> hash;
@@ -87,6 +89,23 @@ struct KeyConverter {
         key.Set(bytes.begin(), bytes.end());
         return key.IsValid();
     }
+
+    template<typename I>
+    bool FromPKBytes(I first, I last, CPubKey& key) const {
+        key.Set(first, last);
+        return key.IsValid();
+    }
+
+    template<typename I>
+    bool FromPKHBytes(I first, I last, CPubKey& key) const {
+        assert(last - first == 20);
+        CKeyID keyid;
+        std::copy(first, last, keyid.begin());
+        auto it = g_testdata->pkmap.find(keyid);
+        assert(it != g_testdata->pkmap.end());
+        key = it->second;
+        return true;
+    }
 };
 
 //! Singleton instance of KeyConverter.
@@ -117,6 +136,9 @@ void Test(const std::string& ms, const std::string& hexscript, int mode)
         BOOST_CHECK_MESSAGE(node->IsNonMalleable() == !!(mode & TESTMODE_NONMAL), "Malleability mismatch: " + ms);
         BOOST_CHECK_MESSAGE(node->NeedsSignature() == !!(mode & TESTMODE_NEEDSIG), "Signature necessity mismatch: " + ms);
         BOOST_CHECK_MESSAGE((node->GetType() << "k"_mst) == !(mode & TESTMODE_TIMELOCKMIX), "Timelock mix mismatch: " + ms);
+        auto inferred_miniscript = miniscript::FromScript(computed_script, CONVERTER);
+        BOOST_CHECK_MESSAGE(inferred_miniscript, "Cannot infer miniscript from script: " + ms);
+        BOOST_CHECK_MESSAGE(inferred_miniscript->ToScript(CONVERTER) == computed_script, "Roundtrip failure: miniscript->script != miniscript->script->miniscript->script: " + ms);
     }
 
 }
@@ -217,6 +239,16 @@ BOOST_AUTO_TEST_CASE(fixed_tests)
     Test("c:or_i(andor(c:pk_h(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65),pk_h(022f01e5e15cca351daff3843fb70f3c2f0a1bdd05e5af888a67784ef3e10a2a01),pk_h(02c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5)),pk_k(02d7924d4f7d43ea965a465ae3095ff41131e5946f3c85f79e44adbcf8e27e080e))", "6376a914fcd35ddacad9f2d5be5e464639441c6065e6955d88ac6476a91406afd46bcdfd22ef94ac122aa11f241244a37ecc886776a9149652d86bedf43ad264362e6e6eba6eb7645081278868672102d7924d4f7d43ea965a465ae3095ff41131e5946f3c85f79e44adbcf8e27e080e68ac", TESTMODE_VALID | TESTMODE_NONMAL | TESTMODE_NEEDSIG);
     Test("thresh(1,c:pk_k(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65),altv:after(1000000000),altv:after(100))", "2103d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65ac6b6300670400ca9a3bb16951686c936b6300670164b16951686c935187", TESTMODE_VALID);
     Test("thresh(2,c:pk_k(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65),ac:pk_k(03fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556),altv:after(1000000000),altv:after(100))", "2103d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65ac6b2103fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556ac6c936b6300670400ca9a3bb16951686c936b6300670164b16951686c935287", TESTMODE_VALID | TESTMODE_NONMAL | TESTMODE_TIMELOCKMIX);
+
+    // Misc unit tests
+    // A Script with a non minimal push is invalid
+    std::vector<unsigned char> nonminpush = ParseHex("0000210232780000feff00ffffffffffff21ff005f00ae21ae00000000060602060406564c2102320000060900fe00005f00ae21ae00100000060606060606000000000000000000000000000000000000000000000000000000000000000000");
+    const CScript nonminpush_script(nonminpush.begin(), nonminpush.end());
+    BOOST_CHECK(miniscript::FromScript(nonminpush_script, CONVERTER) == nullptr);
+    // A non-minimal VERIFY (<key> CHECKSIG VERIFY 1)
+    std::vector<unsigned char> nonminverify = ParseHex("2103a0434d9e47f3c86235477c7b1ae6ae5d3442d49b1943c2b752a68e2a47e247c7ac6951");
+    const CScript nonminverify_script(nonminverify.begin(), nonminverify.end());
+    BOOST_CHECK(miniscript::FromScript(nonminverify_script, CONVERTER) == nullptr);
     // A threshold as large as the number of subs is valid.
     Test("thresh(2,c:pk_k(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65),altv:after(100))", "2103d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65ac6b6300670164b16951686c935287", TESTMODE_VALID | TESTMODE_NEEDSIG | TESTMODE_NONMAL);
     // A threshold of 1 is valid.