-extern bool digest_create(struct digest *, void *indata, size_t inlen, void *outdata);
-extern bool digest_verify(struct digest *, void *indata, size_t inlen, void *digestdata);
+extern bool digest_create(struct digest *, const void *indata, size_t inlen, void *outdata);
+extern bool digest_verify(struct digest *, const void *indata, size_t inlen, const void *digestdata);
+extern bool digest_set_key(struct digest *, const void *key, size_t len);