batch_interface: add batch_context_verify function

added batch_context_verify to the schnorrsig module

Author: siv2r

include/secp256k1_schnorrsig.h

@@ -175,6 +175,21 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_schnorrsig_verify(
     const secp256k1_xonly_pubkey *pubkey
 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(5);
 
+/** Verify the set of schnorr signatures or tweaked pubkeys present in the secp256k1_batch_context.
+ * 
+ *  Returns: 1: correct schnorrsigs/tweaks
+ *           0: incorrect schnorrsigs/tweaks
+ * 
+ *  In particular, returns 1 if the batch context is empty or NULL.
+ * 
+ *  Args:    ctx: a secp256k1 context object (can be initialized for none).
+ *     batch_ctx: a secp256k1 batch context object that contains a 
+ *                set of schnorrsigs/tweaks.
+ */
+SECP256K1_API int secp256k1_batch_context_verify(
+    const secp256k1_context *ctx,
+    secp256k1_batch_context *batch_ctx
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
 
 #ifdef __cplusplus
 }

src/modules/schnorrsig/Makefile.am.include

@@ -3,3 +3,4 @@ noinst_HEADERS += src/modules/schnorrsig/main_impl.h
 noinst_HEADERS += src/modules/schnorrsig/tests_impl.h
 noinst_HEADERS += src/modules/schnorrsig/tests_exhaustive_impl.h
 noinst_HEADERS += src/modules/schnorrsig/bench_impl.h
+noinst_HEADERS += src/modules/schnorrsig/batch_add_impl.h

src/modules/schnorrsig/batch_add_impl.h

@@ -0,0 +1,28 @@
+#ifndef SECP256K1_BATCH_ADD_IMPL_H
+#define SECP256K1_BATCH_ADD_IMPL_H
+
+#include "../../batch_impl.h"
+
+/** Batch verifies the schnorrsig/tweaks present in the batch context object.
+ *  If the batch context is empty, 
+ * 
+ * calls secp256k1_ecmult_strauss_batch on a scratch space filled with 2n points
+ * and 2n scalars, where n = no of terms (user input in secp256k1_batch_context_create)
+ * 
+ * Fails if:
+ * 0 != -(s1 + a2*s2 + ... + au*su)G
+ *      + R1 + a2*R2 + ... + au*Ru + e1*P1 + (a2*e2)P2 + ... + (au*eu)Pu.
+ */
+int secp256k1_batch_verify(const secp256k1_callback* error_callback, secp256k1_batch_context* batch_ctx) {
+    secp256k1_gej resj; 
+
+    if(batch_ctx != NULL && batch_ctx->scalars != NULL && batch_ctx->points != NULL) {
+        batch_ctx->result = secp256k1_ecmult_strauss_batch(error_callback, batch_ctx->data, &resj,  batch_ctx->scalars, batch_ctx->points, &batch_ctx->sc_g, NULL, NULL, batch_ctx->len, 0) && secp256k1_gej_is_infinity(&resj);
+
+        return batch_ctx->result;
+    }
+
+    return 0;
+}
+
+#endif

src/modules/schnorrsig/main_impl.h

@@ -10,6 +10,7 @@
 #include "../../../include/secp256k1.h"
 #include "../../../include/secp256k1_schnorrsig.h"
 #include "../../hash.h"
+#include "batch_add_impl.h"
 
 
 
@@ -266,4 +267,9 @@ int secp256k1_schnorrsig_verify(const secp256k1_context* ctx, const unsigned cha
            secp256k1_fe_equal_var(&rx, &r.x);
 }
 
+int secp256k1_batch_context_verify(const secp256k1_context *ctx, secp256k1_batch_context *batch_ctx) {
+    VERIFY_CHECK(ctx != NULL);
+    return secp256k1_batch_verify(&ctx->error_callback, batch_ctx);
+}
+
 #endif