diff --git a/radicale/auth/htpasswd.py b/radicale/auth/htpasswd.py
index 3b473f28..fb7def4d 100644
--- a/radicale/auth/htpasswd.py
+++ b/radicale/auth/htpasswd.py
@@ -191,37 +191,28 @@ class Auth(auth.BaseAuth):
         return ("ARGON2", argon2.verify(password, hash_value.strip()))
 
     def _md5apr1(self, hash_value: str, password: str) -> tuple[str, bool]:
-        if self._encryption == "autodetect" and len(hash_value) != 37:
-            return self._plain_fallback("MD5-APR1", hash_value, password)
-        else:
-            return ("MD5-APR1", apr_md5_crypt.verify(password, hash_value.strip()))
+        return ("MD5-APR1", apr_md5_crypt.verify(password, hash_value.strip()))
 
     def _sha256(self, hash_value: str, password: str) -> tuple[str, bool]:
-        if self._encryption == "autodetect" and len(hash_value) != 63:
-            return self._plain_fallback("SHA-256", hash_value, password)
-        else:
-            return ("SHA-256", sha256_crypt.verify(password, hash_value.strip()))
+        return ("SHA-256", sha256_crypt.verify(password, hash_value.strip()))
 
     def _sha512(self, hash_value: str, password: str) -> tuple[str, bool]:
-        if self._encryption == "autodetect" and len(hash_value) != 106:
-            return self._plain_fallback("SHA-512", hash_value, password)
-        else:
-            return ("SHA-512", sha512_crypt.verify(password, hash_value.strip()))
+        return ("SHA-512", sha512_crypt.verify(password, hash_value.strip()))
 
     def _autodetect(self, hash_value: str, password: str) -> tuple[str, bool]:
-        if hash_value.startswith("$apr1$", 0, 6):
+        if re.match(r"^\$apr1\$[A-Za-z0-9/.]{8}\$[A-Za-z0-9/.]{22}", hash_value):
             # MD5-APR1
             return self._md5apr1(hash_value, password)
-        elif re.match(r"^\$2(a|b|x|y)?\$", hash_value):
+        elif re.match(r"^\$2(a|b|x|y)?\$[0-9]{2}\$[A-Za-z0-9/.]{53}", hash_value):
             # BCRYPT
             return self._verify_bcrypt(hash_value, password)
         elif re.match(r"^\$argon2(i|d|id)\$", hash_value):
             # ARGON2
             return self._verify_argon2(hash_value, password)
-        elif hash_value.startswith("$5$", 0, 3):
+        elif re.match(r"^\$5\$(rounds=[0-9]+\$)?[A-Za-z0-9/.]{16}\$[A-Za-z0-9/.]{42}", hash_value):
             # SHA-256
             return self._sha256(hash_value, password)
-        elif hash_value.startswith("$6$", 0, 3):
+        elif re.match(r"^\$6\$(rounds=[0-9]+\$)?[A-Za-z0-9/.]{16}\$[A-Za-z0-9/.]{85}", hash_value):
             # SHA-512
             return self._sha512(hash_value, password)
         else: