diff --git a/copyparty/__main__.py b/copyparty/__main__.py
index 7314f9a2..c57fde07 100644
--- a/copyparty/__main__.py
+++ b/copyparty/__main__.py
@@ -65,6 +65,7 @@ from .util import (
     load_resource,
     min_ex,
     pybin,
+    read_utf8,
     termsize,
     wrap,
 )
@@ -255,8 +256,7 @@ def get_srvname(verbose) -> str:
     if verbose:
         lprint("using hostname from {}\n".format(fp))
     try:
-        with open(fp, "rb") as f:
-            ret = f.read().decode("utf-8", "replace").strip()
+        return read_utf8(None, fp, True).strip()
     except:
         ret = ""
         namelen = 5
@@ -265,47 +265,18 @@ def get_srvname(verbose) -> str:
             ret = re.sub("[234567=]", "", ret)[:namelen]
         with open(fp, "wb") as f:
             f.write(ret.encode("utf-8") + b"\n")
-
-    return ret
+        return ret
 
 
-def get_fk_salt() -> str:
-    fp = os.path.join(E.cfg, "fk-salt.txt")
+def get_salt(name: str, nbytes: int) -> str:
+    fp = os.path.join(E.cfg, "%s-salt.txt" % (name,))
     try:
-        with open(fp, "rb") as f:
-            ret = f.read().strip()
+        return read_utf8(None, fp, True).strip()
     except:
-        ret = b64enc(os.urandom(18))
+        ret = b64enc(os.urandom(nbytes))
         with open(fp, "wb") as f:
             f.write(ret + b"\n")
-
-    return ret.decode("utf-8")
-
-
-def get_dk_salt() -> str:
-    fp = os.path.join(E.cfg, "dk-salt.txt")
-    try:
-        with open(fp, "rb") as f:
-            ret = f.read().strip()
-    except:
-        ret = b64enc(os.urandom(30))
-        with open(fp, "wb") as f:
-            f.write(ret + b"\n")
-
-    return ret.decode("utf-8")
-
-
-def get_ah_salt() -> str:
-    fp = os.path.join(E.cfg, "ah-salt.txt")
-    try:
-        with open(fp, "rb") as f:
-            ret = f.read().strip()
-    except:
-        ret = b64enc(os.urandom(18))
-        with open(fp, "wb") as f:
-            f.write(ret + b"\n")
-
-    return ret.decode("utf-8")
+        return ret.decode("utf-8")
 
 
 def ensure_locale() -> None:
@@ -1552,9 +1523,9 @@ def run_argparse(
 
     cert_path = os.path.join(E.cfg, "cert.pem")
 
-    fk_salt = get_fk_salt()
-    dk_salt = get_dk_salt()
-    ah_salt = get_ah_salt()
+    fk_salt = get_salt("fk", 18)
+    dk_salt = get_salt("dk", 30)
+    ah_salt = get_salt("ah", 18)
 
     # alpine peaks at 5 threads for some reason,
     # all others scale past that (but try to avoid SMT),
diff --git a/copyparty/authsrv.py b/copyparty/authsrv.py
index ee2c7434..db9c1cdd 100644
--- a/copyparty/authsrv.py
+++ b/copyparty/authsrv.py
@@ -33,6 +33,7 @@ from .util import (
     get_df,
     humansize,
     odfusion,
+    read_utf8,
     relchk,
     statdir,
     ub64enc,
@@ -2547,8 +2548,8 @@ class AuthSrv(object):
             if not bos.path.exists(ap):
                 pwdb = {}
             else:
-                with open(ap, "r", encoding="utf-8") as f:
-                    pwdb = json.load(f)
+                jtxt = read_utf8(self.log, ap, True)
+                pwdb = json.loads(jtxt)
 
             pwdb = [x for x in pwdb if x[0] != uname]
             pwdb.append((uname, self.defpw[uname], hpw))
@@ -2571,8 +2572,8 @@ class AuthSrv(object):
         if not self.args.chpw or not bos.path.exists(ap):
             return
 
-        with open(ap, "r", encoding="utf-8") as f:
-            pwdb = json.load(f)
+        jtxt = read_utf8(self.log, ap, True)
+        pwdb = json.loads(jtxt)
 
         useen = set()
         urst = set()
@@ -3068,8 +3069,9 @@ def expand_config_file(
     ipath += " -> " + fp
     ret.append("#\033[36m opening cfg file{}\033[0m".format(ipath))
 
-    with open(fp, "rb") as f:
-        for oln in [x.decode("utf-8").rstrip() for x in f]:
+    cfg_lines = read_utf8(log, fp, True).split("\n")
+    if True:  # diff-golf
+        for oln in [x.rstrip() for x in cfg_lines]:
             ln = oln.split("  #")[0].strip()
             if ln.startswith("% "):
                 pad = " " * len(oln.split("%")[0])
diff --git a/copyparty/httpcli.py b/copyparty/httpcli.py
index 116b7320..f439d6c1 100644
--- a/copyparty/httpcli.py
+++ b/copyparty/httpcli.py
@@ -87,6 +87,7 @@ from .util import (
     quotep,
     rand_name,
     read_header,
+    read_utf8,
     read_socket,
     read_socket_chunked,
     read_socket_unbounded,
@@ -870,8 +871,7 @@ class HttpCli(object):
             html = html.replace("%", "", 1)
 
         if html.startswith("@"):
-            with open(html[1:], "rb") as f:
-                html = f.read().decode("utf-8")
+            html = read_utf8(self.log, html[1:], True)
 
         if html.startswith("%"):
             html = html[1:]
@@ -3740,8 +3740,7 @@ class HttpCli(object):
                     continue
                 fn = "%s/%s" % (abspath, fn)
                 if bos.path.isfile(fn):
-                    with open(fsenc(fn), "rb") as f:
-                        logues[n] = f.read().decode("utf-8")
+                    logues[n] = read_utf8(self.log, fsenc(fn), False)
                     if "exp" in vn.flags:
                         logues[n] = self._expand(
                             logues[n], vn.flags.get("exp_lg") or []
@@ -3762,9 +3761,8 @@ class HttpCli(object):
             for fn in fns:
                 fn = "%s/%s" % (abspath, fn)
                 if bos.path.isfile(fn):
-                    with open(fsenc(fn), "rb") as f:
-                        txt = f.read().decode("utf-8")
-                        break
+                    txt = read_utf8(self.log, fsenc(fn), False)
+                    break
 
             if txt and "exp" in vn.flags:
                 txt = self._expand(txt, vn.flags.get("exp_md") or [])
@@ -6254,9 +6252,7 @@ class HttpCli(object):
                 docpath = os.path.join(abspath, doc)
                 sz = bos.path.getsize(docpath)
                 if sz < 1024 * self.args.txt_max:
-                    with open(fsenc(docpath), "rb") as f:
-                        doctxt = f.read().decode("utf-8", "replace")
-
+                    doctxt = read_utf8(self.log, fsenc(docpath), False)
                     if doc.lower().endswith(".md") and "exp" in vn.flags:
                         doctxt = self._expand(doctxt, vn.flags.get("exp_md") or [])
                 else:
diff --git a/copyparty/util.py b/copyparty/util.py
index c17c451e..692d3dfa 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -594,6 +594,38 @@ except Exception as ex:
         print("using fallback base64 codec due to %r" % (ex,))
 
 
+class NotUTF8(Exception):
+    pass
+
+
+def read_utf8(log: Optional["NamedLogger"], ap: Union[str, bytes], strict: bool) -> str:
+    with open(ap, "rb") as f:
+        buf = f.read()
+
+    try:
+        return buf.decode("utf-8", "strict")
+    except UnicodeDecodeError as ex:
+        eo = ex.start
+        eb = buf[eo : eo + 1]
+
+    if not strict:
+        t = "WARNING: The file [%s] is not using the UTF-8 character encoding; some characters in the file will be skipped/ignored. The first unreadable character was byte %r at offset %d. Please convert this file to UTF-8 by opening the file in your text-editor and saving it as UTF-8."
+        t = t % (ap, eb, eo)
+        if log:
+            log(t, 3)
+        else:
+            print(t)
+        return buf.decode("utf-8", "replace")
+
+    t = "ERROR: The file [%s] is not using the UTF-8 character encoding, and cannot be loaded. The first unreadable character was byte %r at offset %d. Please convert this file to UTF-8 by opening the file in your text-editor and saving it as UTF-8."
+    t = t % (ap, eb, eo)
+    if log:
+        log(t, 3)
+    else:
+        print(t)
+    raise NotUTF8(t)
+
+
 class Daemon(threading.Thread):
     def __init__(
         self,