ecdsa-s2c: block in module

Co-authored-by: Marko Bencun <mbencun+pgp@gmail.com>
Co-authored-by: Jonas Nick <jonasd.nick@gmail.com>

include/secp256k1_ecdsa_s2c.h

@@ -0,0 +1,58 @@
+#ifndef SECP256K1_ECDSA_S2C_H
+#define SECP256K1_ECDSA_S2C_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Data structure that holds a sign-to-contract ("s2c") opening information.
+ *  Sign-to-contract allows a signer to commit to some data as part of a signature. It
+ *  can be used as an Out-argument in certain signing functions.
+ *
+ *  The exact representation of data inside is implementation defined and not
+ *  guaranteed to be portable between different platforms or versions. It is
+ *  however guaranteed to be 64 bytes in size, and can be safely copied/moved.
+ *  If you need to convert to a format suitable for storage, transmission, or
+ *  comparison, use secp256k1_ecdsa_s2c_opening_serialize and secp256k1_ecdsa_s2c_opening_parse.
+ */
+typedef struct {
+    unsigned char data[64];
+} secp256k1_ecdsa_s2c_opening;
+
+/** Parse a sign-to-contract opening.
+ *
+ *  Returns: 1 if the opening could be parsed
+ *           0 if the opening could not be parsed
+ *  Args:    ctx: a secp256k1 context object.
+ *  Out: opening: pointer to an opening object. If 1 is returned, it is set to a
+ *                parsed version of input. If not, its value is unspecified.
+ *  In:  input33: pointer to 33-byte array with a serialized opening
+ *
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_s2c_opening_parse(
+    const secp256k1_context* ctx,
+    secp256k1_ecdsa_s2c_opening* opening,
+    const unsigned char* input33
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+
+/** Serialize a sign-to-contract opening into a byte sequence.
+ *
+ *  Returns: 1 if the opening was successfully serialized.
+ *           0 if the opening could not be serialized
+ *  Args:     ctx: a secp256k1 context object
+ *  Out: output33: pointer to a 33-byte array to place the serialized opening in
+ *  In:   opening: a pointer to an initialized `secp256k1_ecdsa_s2c_opening`
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_s2c_opening_serialize(
+    const secp256k1_context* ctx,
+    unsigned char* output33,
+    const secp256k1_ecdsa_s2c_opening* opening
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_ECDSA_S2C_H */