support hashed passwords; closes #39

docs/devnotes.md

@@ -4,8 +4,9 @@
 * [future plans](#future-plans) - some improvement ideas
 * [design](#design)
     * [up2k](#up2k) - quick outline of the up2k protocol
-    * [why not tus](#why-not-tus) - I didn't know about [tus](https://tus.io/)
-    * [why chunk-hashes](#why-chunk-hashes) - a single sha512 would be better, right?
+        * [why not tus](#why-not-tus) - I didn't know about [tus](https://tus.io/)
+        * [why chunk-hashes](#why-chunk-hashes) - a single sha512 would be better, right?
+* [hashed passwords](#hashed-passwords) - regarding the curious decisions
 * [http api](#http-api)
     * [read](#read)
     * [write](#write)
@@ -68,14 +69,14 @@ regarding the frequent server log message during uploads;
 * on this http connection, `2.77 GiB` transferred, `102.9 MiB/s` average, `948` chunks handled
 * client says `4` uploads OK, `0` failed, `3` busy, `1` queued, `10042 MiB` total size, `7198 MiB` and `00:01:09` left
 
-## why not tus
+### why not tus
 
 I didn't know about [tus](https://tus.io/)  when I made this, but:
 * up2k has the advantage that it supports parallel uploading of non-contiguous chunks straight into the final file -- [tus does a merge at the end](https://tus.io/protocols/resumable-upload.html#concatenation) which is slow and taxing on the server HDD / filesystem (unless i'm misunderstanding)
 * up2k has the slight disadvantage of requiring the client to hash the entire file before an upload can begin, but this has the benefit of immediately skipping duplicate files
   * and the hashing happens in a separate thread anyways so it's usually not a bottleneck
 
-## why chunk-hashes
+### why chunk-hashes
 
 a single sha512 would be better, right?
 
@@ -92,6 +93,15 @@ hashwasm would solve the streaming issue but reduces hashing speed for sha512 (x
 * blake2 might be a better choice since xxh is non-cryptographic, but that gets ~15 MiB/s on slower androids
 
 
+# hashed passwords
+
+regarding the curious decisions
+
+there is a static salt for all passwords;
+* because most copyparty APIs allow users to authenticate using only their password, making the username unknown, so impossible to do per-account salts
+* the drawback of this is that an attacker can bruteforce all accounts in parallel, however most copyparty instances only have a handful of accounts in the first place, and it can be compensated by increasing the hashing cost anyways
+
+
 # http api
 
 * table-column `params` = URL parameters; `?foo=bar&qux=...`