diff --git a/searx/engine_cache.py b/searx/engine_cache.py
new file mode 100644
index 000000000..67e5fd1dd
--- /dev/null
+++ b/searx/engine_cache.py
@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""This provides an easy to use interface for engine implementations to store and read key-value pairs.
+
+For instance, this can be used to remember programmatically extracted API keys or other kinds of secret tokens.
+"""
+
+from typing import Optional
+from searx import redisdb, redislib
+
+
+class EngineCache:
+    def store(self, key: str, value: str):
+        pass
+
+    def get(self, key: str) -> Optional[str]:
+        pass
+
+
+class MemoryEngineCache(EngineCache):
+    def __init__(self, max_size: int = 100):
+        self.__STORAGE = {}
+        self.max_size = max_size
+
+    def store(self, key, value):
+        """Store the provided key-value pair in the cache."""
+        if len(self.__STORAGE) > self.max_size:
+            self.__STORAGE.popitem()
+
+        # remove the old value in order to add the new value to the top
+        # of the dictionary, as dictionaries are ordered since Python 3.7
+        if key in self.__STORAGE:
+            self.__STORAGE.pop(key)
+
+        self.__STORAGE[key] = value
+
+    def get(self, key):
+        return self.__STORAGE.get(key)
+
+
+class RedisEngineCache(EngineCache):
+    def __init__(self, key_prefix: str, expiration_seconds: int = 600):
+        self.key_prefix = key_prefix
+        self.expiration_seconds = expiration_seconds
+
+    def _get_cache_key(self, key):
+        return self.key_prefix + redislib.secret_hash(key)
+
+    def store(self, key, value):
+        c = redisdb.client()
+
+        cache_key = self._get_cache_key(key)
+        c.set(cache_key, value, ex=self.expiration_seconds)
+
+    def get(self, key):
+        c = redisdb.client()
+
+        cache_key = self._get_cache_key(key)
+        value = c.get(cache_key)
+        if value or value == b'':
+            return value
+
+        return None
+
+
+def get_or_create_cache(database_prefix: str) -> EngineCache:
+    if redisdb.client():
+        return RedisEngineCache(database_prefix)
+
+    return MemoryEngineCache()
diff --git a/searx/engines/duckduckgo.py b/searx/engines/duckduckgo.py
index 450cd9cf8..4a03daa10 100644
--- a/searx/engines/duckduckgo.py
+++ b/searx/engines/duckduckgo.py
@@ -15,7 +15,6 @@ import lxml.html
 
 from searx import (
     locales,
-    redislib,
     external_bang,
 )
 from searx.utils import (
@@ -25,7 +24,7 @@ from searx.utils import (
     extract_text,
 )
 from searx.network import get  # see https://github.com/searxng/searxng/issues/762
-from searx import redisdb
+from searx.engine_cache import get_or_create_cache, EngineCache
 from searx.enginelib.traits import EngineTraits
 from searx.exceptions import SearxEngineCaptchaException
 from searx.result_types import EngineResults
@@ -61,25 +60,23 @@ url = "https://html.duckduckgo.com/html"
 
 time_range_dict = {'day': 'd', 'week': 'w', 'month': 'm', 'year': 'y'}
 form_data = {'v': 'l', 'api': 'd.js', 'o': 'json'}
-__CACHE = []
+
+__CACHE: EngineCache = get_or_create_cache('SearXNG_ddg_web_vqd')
 
 
-def _cache_key(query: str, region: str):
-    return 'SearXNG_ddg_web_vqd' + redislib.secret_hash(f"{query}//{region}")
+def init(_):
+    global __CACHE  # pylint: disable=global-statement
+    __CACHE = get_or_create_cache('SearXNG_ddg_web_vqd')
+    # TODO: why is the __CACHE always None if initialized as None,
+    # even though it should be changed here and this method is
+    # confirmed to be called? ...
 
 
 def cache_vqd(query: str, region: str, value: str):
     """Caches a ``vqd`` value from a query."""
-    c = redisdb.client()
-    if c:
-        logger.debug("VALKEY cache vqd value: %s (%s)", value, region)
-        c.set(_cache_key(query, region), value, ex=600)
 
-    else:
-        logger.debug("MEM cache vqd value: %s (%s)", value, region)
-        if len(__CACHE) > 100:  # cache vqd from last 100 queries
-            __CACHE.pop(0)
-        __CACHE.append((_cache_key(query, region), value))
+    __CACHE.store(f"{query}//{region}", value)
+    logger.debug("cached vqd value: %s (%s)", value, region)
 
 
 def get_vqd(query: str, region: str, force_request: bool = False):
@@ -114,20 +111,10 @@ def get_vqd(query: str, region: str, force_request: bool = False):
     seems the block list is a sliding window: to get my IP rid from the bot list
     I had to cool down my IP for 1h (send no requests from that IP to DDG).
     """
-    key = _cache_key(query, region)
-
-    c = redisdb.client()
-    if c:
-        value = c.get(key)
-        if value or value == b'':
-            value = value.decode('utf-8')  # type: ignore
-            logger.debug("re-use CACHED vqd value: %s", value)
-            return value
-
-    for k, value in __CACHE:
-        if k == key:
-            logger.debug("MEM re-use CACHED vqd value: %s", value)
-            return value
+    value = __CACHE.get(f"{query}//{region}")
+    if value is not None:
+        logger.debug("re-use CACHED vqd value: %s", value)
+        return value
 
     if force_request:
         resp = get(f'https://duckduckgo.com/?q={quote_plus(query)}')