Add flag to sort multisig keys (BIP67)

include/wally_script.h

@@ -31,9 +31,10 @@ extern "C" {
 #define WALLY_WITNESSSCRIPT_MAX_LEN   35 /** (PUSH OF)0 [SHA256] */
 
 /* Script creation flags */
-#define WALLY_SCRIPT_HASH160  0x1 /** hash160 input bytes before using them */
-#define WALLY_SCRIPT_SHA256   0x2 /** sha256 input bytes before using them */
-#define WALLY_SCRIPT_AS_PUSH  0x4 /** Return a push of the generated script */
+#define WALLY_SCRIPT_HASH160          0x1 /** hash160 input bytes before using them */
+#define WALLY_SCRIPT_SHA256           0x2 /** sha256 input bytes before using them */
+#define WALLY_SCRIPT_AS_PUSH          0x4 /** Return a push of the generated script */
+#define WALLY_SCRIPT_MULTISIG_SORTED  0x8 /** Sort public keys (BIP67) */
 
 /* Script opcodes */
 #define OP_0 0x00
@@ -326,7 +327,7 @@ WALLY_CORE_API int wally_scriptpubkey_p2sh_from_bytes(
  * :param bytes: Compressed public keys to create a scriptPubkey from.
  * :param bytes_len: Length of ``bytes`` in bytes. Must be a multiple of ``EC_PUBLIC_KEY_LEN``.
  * :param threshold: The number of signatures that must match to satisfy the script.
- * :param flags: Must be zero.
+ * :param flags: Must be ``WALLY_SCRIPT_MULTISIG_SORTED`` for BIP67 sorting or 0.
  * :param bytes_out: Destination for the resulting scriptPubkey.
  * :param len: The length of ``bytes_out`` in bytes.
  * :param written: Destination for the number of bytes written to ``bytes_out``.

src/script.c

@@ -541,34 +541,46 @@ int wally_scriptpubkey_p2sh_from_bytes(
     return ret;
 }
 
+static int pubkey_compare(const void *a, const void *b)
+{
+    return memcmp(a, b, EC_PUBLIC_KEY_LEN);
+}
+
 int wally_scriptpubkey_multisig_from_bytes(
     const unsigned char *bytes, size_t bytes_len, uint32_t threshold,
     uint32_t flags, unsigned char *bytes_out, size_t len, size_t *written)
 {
     size_t n_pubkeys = bytes_len / EC_PUBLIC_KEY_LEN;
     size_t script_len = 3 + (n_pubkeys * (EC_PUBLIC_KEY_LEN + 1));
     size_t i;
+    unsigned char pubkey_bytes[16 * EC_PUBLIC_KEY_LEN];
 
     if (written)
         *written = 0;
 
     if (!bytes || !bytes_len || bytes_len % EC_PUBLIC_KEY_LEN ||
         n_pubkeys < 1 || n_pubkeys > 16 || threshold < 1 || threshold > 16 ||
-        threshold > n_pubkeys || flags || !bytes_out || !written)
+        threshold > n_pubkeys || (flags & ~WALLY_SCRIPT_MULTISIG_SORTED) ||
+        !bytes_out || !written)
         return WALLY_EINVAL;
 
     if (len < script_len) {
         *written = script_len;
         return WALLY_OK;
     }
 
+    memcpy(pubkey_bytes, bytes, bytes_len);
+    if (flags & WALLY_SCRIPT_MULTISIG_SORTED) {
+        qsort(pubkey_bytes, n_pubkeys, EC_PUBLIC_KEY_LEN, pubkey_compare);
+    }
+
     *bytes_out++ = v_to_op_n(threshold);
     for (i = 0; i < n_pubkeys; ++i) {
         *bytes_out++ = EC_PUBLIC_KEY_LEN;
-        memcpy(bytes_out, bytes, EC_PUBLIC_KEY_LEN);
+        memcpy(bytes_out, pubkey_bytes + i * EC_PUBLIC_KEY_LEN, EC_PUBLIC_KEY_LEN);
         bytes_out += EC_PUBLIC_KEY_LEN;
-        bytes += EC_PUBLIC_KEY_LEN;
     }
+    wally_clear(pubkey_bytes, sizeof(pubkey_bytes));
     *bytes_out++ = v_to_op_n(n_pubkeys);
     *bytes_out = OP_CHECKMULTISIG;
     *written = script_len;

src/test/test_script.py

@@ -6,6 +6,8 @@
 SCRIPT_TYPE_P2SH = 0x4
 SCRIPT_TYPE_MULTISIG = 0x20
 
+WALLY_SCRIPT_MULTISIG_SORTED = 0x8
+
 SCRIPT_HASH160 = 0x1
 SCRIPT_SHA256  = 0x2
 
@@ -21,7 +23,10 @@
 PKU, PKU_LEN = make_cbuffer('11' * 65) # Fake uncompressed pubkey
 SH, SH_LEN = make_cbuffer('11' * 20)  # Fake script hash
 MPK_2, MPK_2_LEN = make_cbuffer('11' * 33 * 2) # Fake multiple (2) pubkeys
-MPK_3, MPK_3_LEN = make_cbuffer('11' * 33 * 3) # Fake multiple (3) pubkeys
+MPK_3, MPK_3_LEN =  make_cbuffer('11' * 33 * 3) # Fake multiple (3) pubkeys
+MPK_3_SORTED, MPK_3_SORTED_LEN =  make_cbuffer('01'*33 + '10'*33 + '11'*33) # Fake multiple (3) sorted pubkeys
+MPK_3_SORTED_REVERSE, MPK_3_SORTED_LEN =  make_cbuffer('11'*33 + '10'*33 + '01'*33) # Fake multiple (3) sorted pubkeys, in reverse order
+MPK_3_SORTED_KEY_PUSH = '21'+'01'*33 + '21'+'10'*33 + '21'+'11'*33
 MPK_17, MPK_17_LEN = make_cbuffer('11' * 33 * 17) # Fake multiple (17) pubkeys
 
 SIG, SIG_LEN = make_cbuffer('11' * 64) # Fake signature
@@ -156,6 +161,9 @@ def test_scriptpubkey_multisig_from_bytes(self):
             [(MPK_3, MPK_3_LEN, 1, 0, out, out_len), '51'+('21'+'11'*33)*3+'53ae'], # 1of3
             [(MPK_3, MPK_3_LEN, 2, 0, out, out_len), '52'+('21'+'11'*33)*3+'53ae'], # 2of3
             [(MPK_3, MPK_3_LEN, 3, 0, out, out_len), '53'+('21'+'11'*33)*3+'53ae'], # 3of3
+            [(MPK_3_SORTED, MPK_3_SORTED_LEN, 1, 0, out, out_len), '51'+ MPK_3_SORTED_KEY_PUSH + '53ae'], # 1of3 sorted
+            [(MPK_3_SORTED, MPK_3_SORTED_LEN, 1, WALLY_SCRIPT_MULTISIG_SORTED, out, out_len), '51'+ MPK_3_SORTED_KEY_PUSH + '53ae'], # 1of3 sorted (WALLY_SCRIPT_MULTISIG_SORTED should have no effect)
+            [(MPK_3_SORTED_REVERSE, MPK_3_SORTED_LEN, 1, WALLY_SCRIPT_MULTISIG_SORTED, out, out_len), '51'+ MPK_3_SORTED_KEY_PUSH + '53ae'], # 1of3 sorted reverse (BIP67)
         ]
         for args, exp_script in valid_args:
             script_len = 3 + (args[1] // 33 * (33 + 1))