1 files changed, 63 insertions, 0 deletions
diff --git a/include/secp256k1_ecdh.h b/include/secp256k1_ecdh.h
new file mode 100644
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--- /dev/null
+++ b/include/secp256k1_ecdh.h
@@ -0,0 +1,63 @@
+#ifndef SECP256K1_ECDH_H
+#define SECP256K1_ECDH_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** A pointer to a function that hashes an EC point to obtain an ECDH secret
+ *
+ *  Returns: 1 if the point was successfully hashed.
+ *           0 will cause secp256k1_ecdh to fail and return 0.
+ *           Other return values are not allowed, and the behaviour of
+ *           secp256k1_ecdh is undefined for other return values.
+ *  Out:     output:     pointer to an array to be filled by the function
+ *  In:      x32:        pointer to a 32-byte x coordinate
+ *           y32:        pointer to a 32-byte y coordinate
+ *           data:       arbitrary data pointer that is passed through
+ */
+typedef int (*secp256k1_ecdh_hash_function)(
+  unsigned char *output,
+  const unsigned char *x32,
+  const unsigned char *y32,
+  void *data
+);
+
+/** An implementation of SHA256 hash function that applies to compressed public key.
+ * Populates the output parameter with 32 bytes. */
+SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256;
+
+/** A default ECDH hash function (currently equal to secp256k1_ecdh_hash_function_sha256).
+ * Populates the output parameter with 32 bytes. */
+SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default;
+
+/** Compute an EC Diffie-Hellman secret in constant time
+ *
+ *  Returns: 1: exponentiation was successful
+ *           0: scalar was invalid (zero or overflow) or hashfp returned 0
+ *  Args:    ctx:        pointer to a context object.
+ *  Out:     output:     pointer to an array to be filled by hashfp.
+ *  In:      pubkey:     pointer to a secp256k1_pubkey containing an initialized public key.
+ *           seckey:     a 32-byte scalar with which to multiply the point.
+ *           hashfp:     pointer to a hash function. If NULL,
+ *                       secp256k1_ecdh_hash_function_sha256 is used
+ *                       (in which case, 32 bytes will be written to output).
+ *           data:       arbitrary data pointer that is passed through to hashfp
+ *                       (can be NULL for secp256k1_ecdh_hash_function_sha256).
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
+  const secp256k1_context *ctx,
+  unsigned char *output,
+  const secp256k1_pubkey *pubkey,
+  const unsigned char *seckey,
+  secp256k1_ecdh_hash_function hashfp,
+  void *data
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_ECDH_H */