batch_add: use enum instead of a string for batch_add_type

Author: siv2r

src/modules/batch/main_impl.h

@@ -11,6 +11,13 @@
 #include "src/hash.h"
 #include "src/scratch.h"
 
+/* Assume two batch objects batch1 and batch2. If we call
+ * batch_add_tweaks on batch1 and batch_add_schnorrsig on batch2.
+ * In this case same randomizer will be created if the bytes added to
+ * batch1->sha and batch2->sha are same. Including this tag during
+ * randomizer generation prevents such mishaps. */
+enum batch_add_type {schnorrsig = 1, tweak_check = 2};
+
 /** Opaque data structure that holds information required for the batch verification.
  *
  *  Members:

src/modules/extrakeys/batch_add_impl.h

@@ -11,11 +11,7 @@
 
 static void secp256k1_batch_xonlypub_tweak_randomizer_gen(unsigned char *randomizer32, secp256k1_sha256 *sha256, const unsigned char *tweaked_pubkey32, const unsigned char *tweaked_pk_parity, const unsigned char *internal_pk33, const unsigned char *tweak32) {
     secp256k1_sha256 sha256_cpy;
-    /* Assume two batch objects batch1 and batch2. If we call
-     * batch_add_tweaks on batch1 and batch_add_schnorrsig on batch2.
-     * In this case same randomizer will be created if the bytes added to
-     * batch1->sha and batch2->sha are same. This tag prevents such cases. */
-    unsigned char batch_add_type[1] = "2";
+    unsigned char batch_add_type[1] = tweak_check;
 
     secp256k1_sha256_write(sha256, batch_add_type, sizeof(batch_add_type));
     /* add tweaked pubkey check data to sha object */

src/modules/schnorrsig/batch_add_impl.h

@@ -11,11 +11,8 @@
 
 static void secp256k1_batch_schnorrsig_randomizer_gen(unsigned char *randomizer32, secp256k1_sha256 *sha256, const unsigned char *sig64, const unsigned char *msg, size_t msglen, const unsigned char *compressed_pk33) {
     secp256k1_sha256 sha256_cpy;
-    unsigned char batch_add_type[1] = "1";
-    /* Assume two batch objects batch1 and batch2. If we call
-     * batch_add_tweaks on batch1 and batch_add_schnorrsig on batch2.
-     * In this case same randomizer will be created if the bytes added to
-     * batch1->sha and batch2->sha are same. This tag prevents such cases. */
+    unsigned char batch_add_type[1] = schnorrsig;
+
     secp256k1_sha256_write(sha256, batch_add_type, sizeof(batch_add_type));
     /* add schnorrsig data to sha256 object */
     secp256k1_sha256_write(sha256, sig64, 64);