diff --git a/client/src/crypto.test.ts b/client/src/crypto.test.ts
index 53c92bb..fc8a4b5 100644
--- a/client/src/crypto.test.ts
+++ b/client/src/crypto.test.ts
@@ -1,4 +1,8 @@
 import { assertEquals } from "https://deno.land/std@0.174.0/testing/asserts.ts";
-import { hash } from "./crypto.ts";
+import { inputToCacheKey } from "./crypto.ts";
 
-Deno.test("hash stability", () => assertEquals(hash("hello"), "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"));
+Deno.test("hash stability", () =>
+    assertEquals(
+        inputToCacheKey("my secret", undefined)("hello"),
+        "413ddc7b60b9f03f95a4091496d05d785478a8b2ac36907c635076879f2d73c3",
+    ));
diff --git a/client/src/crypto.ts b/client/src/crypto.ts
index c193722..1d854cd 100644
--- a/client/src/crypto.ts
+++ b/client/src/crypto.ts
@@ -2,6 +2,7 @@ import {
   bufferToHex,
   hexToBuffer,
 } from "https://deno.land/x/hextools@v1.0.0/mod.ts";
+import { jsonStringify } from "https://deno.land/x/stable_stringify@v0.2.1/jsonStringify.ts";
 
 import { decode as base64UrlDecode } from "https://deno.land/std@0.82.0/encoding/base64url.ts";
 import { sha256 } from "https://denopkg.com/chiefbiiko/sha256@v1.0.0/mod.ts";
@@ -11,7 +12,7 @@ const algo = "AES-CBC";
 const getKey = (scope: "encrypt" | "decrypt", key: string) =>
   crypto.subtle.importKey("raw", base64UrlDecode(key), algo, true, [scope]);
 
-export const hash = (x: string): string => sha256(x, "utf8", "hex") as string;
+const hash = (x: string): string => sha256(x, "utf8", "hex") as string;
 
 export const encrypt =
   (key: string) => async (plainText: string): Promise<Encrypted> => {
@@ -45,3 +46,15 @@ export const decrypt = (key: string) => async ({ iv, cipher }: Encrypted) =>
       ),
     ),
   );
+
+// deno-lint-ignore no-explicit-any
+export type CustomKeyFn = (..._: any[]) => any;
+
+export const jsonStableStringify = <Args>(x: Args) =>
+  jsonStringify(x) as string;
+
+export const inputToCacheKey =
+  // deno-lint-ignore no-explicit-any
+  <Args extends any[]>(secret: string, customKeyFn: CustomKeyFn | undefined) =>
+  (...x: Args): string =>
+    hash(jsonStableStringify(customKeyFn ? customKeyFn(...x) : x) + secret);
diff --git a/client/src/index.test.ts b/client/src/index.test.ts
index 045c317..b32c3bd 100644
--- a/client/src/index.test.ts
+++ b/client/src/index.test.ts
@@ -1,4 +1,4 @@
-import { CacheParams, cache, waitAllWrites } from "./index.ts";
+import { cache, type CacheParams, waitAllWrites } from "./index.ts";
 
 import { assertEquals } from "https://deno.land/std@0.174.0/testing/asserts.ts";
 import { config } from "https://deno.land/x/dotenv@v3.2.2/mod.ts";
diff --git a/client/src/index.ts b/client/src/index.ts
index a646fe6..4527502 100644
--- a/client/src/index.ts
+++ b/client/src/index.ts
@@ -1,9 +1,12 @@
-import { decrypt, encrypt, hash } from "./crypto.ts";
+import {
+  CustomKeyFn,
+  decrypt,
+  encrypt,
+  inputToCacheKey,
+  jsonStableStringify,
+} from "./crypto.ts";
 
 import { dirname } from "https://deno.land/std@0.179.0/path/mod.ts";
-import { jsonStringify } from "https://deno.land/x/stable_stringify@v0.2.1/jsonStringify.ts";
-
-const jsonStableStringify = <Args>(x: Args) => jsonStringify(x) as string;
 
 const writeStringToFile = (filePath: string, s: string) =>
   Deno.mkdir(dirname(filePath), { recursive: true }).then(() =>
@@ -100,18 +103,9 @@ const abstractCache = <F extends Func>({
 
 export const waitAllWrites = () => Promise.all(writePromises);
 
-// deno-lint-ignore no-explicit-any
-type CustomKeyFn = (..._: any[]) => any;
-
-export const inputToCacheKey =
-  // deno-lint-ignore no-explicit-any
-  <Args extends any[]>(secret: string, customKeyFn: CustomKeyFn | undefined) =>
-  (...x: Args): string =>
-    hash(jsonStableStringify(customKeyFn ? customKeyFn(...x) : x) + secret);
-
 type MemParams = {
   ttl?: number;
-  customKeyFn?: (..._: any[]) => string;
+  customKeyFn?: CustomKeyFn;
   forceWrite?: boolean;
 };