-/* Returns public key as a malloced hex string */
-typedef string_t dh_makepublic_fn(void *st, uint8_t *secret,
- int32_t secretlen);
-/* Fills buffer (up to buflen) with shared secret */
-typedef void dh_makeshared_fn(void *st, uint8_t *secret,
- int32_t secretlen, cstring_t rempublic,
- uint8_t *sharedsecret, int32_t buflen);
+/* Write public value corresponding to the secret to the public buffer, and
+ * return its actual length. The size of the buffer is given in publiclen,
+ * which will be at least the public_len reported by the closure. The
+ * secretlen will be the secret_len reported by the closure. This operation
+ * is not expected to fail.
+ */
+typedef int32_t dh_makepublic_fn(void *st, void *public, int32_t publiclen,
+ uint8_t *secret, int32_t secretlen);
+
+/* Fills buffer (up to buflen) with shared secret. The publiclen comes from
+ * the remote site, and may not be acceptable, though it has been checked for
+ * memory-safety. The secretlen and buflen are the secret_len and shared_len
+ * reported by the closure, respectively. Return false on faliure (e.g., if
+ * the publiclen is unacceptable).
+ */
+typedef bool_t dh_makeshared_fn(void *st,
+ uint8_t *secret, int32_t secretlen,
+ const void *public, int32_t publiclen,
+ uint8_t *sharedsecret, int32_t buflen);
+