diff --git a/src/index.ts b/src/index.ts
index cf00653..6b58d10 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -12,7 +12,111 @@
  */
 
 export default {
-    async fetch(request, env, ctx): Promise<Response> {
-        return new Response("Hello World!");
+    async fetch(request: Request, env: Env, ctx: ExecutionContext<unknown>): Promise<Response> {
+        try {
+            const isValid = await verifySignature(request, env);
+            if (!isValid) {
+                return new Response("Invalid Signature", { status: 403 });
+            }
+
+            const url = new URL(request.url);
+            const method = request.method;
+
+            // メモリ節約のためにReadableStream
+            return new Response(`Verified ${method} for ${url.pathname}`, { status: 200 });
+        } catch (e) {
+            const error = e as Error;
+            return new Response(error.message, { status: 500 });
+        }
     },
 } satisfies ExportedHandler<Env>;
+
+interface Env {
+    ACCESS_KEY: string;
+    SECRET_KEY: string;
+    REGION: string;
+}
+
+async function verifySignature(request: Request, env: Env): Promise<boolean> {
+    const url = new URL(request.url);
+    const headers = request.headers;
+
+    const isQueryAuth = url.searchParams.has("X-Amz-Algorithm");
+    const authHeader = headers.get("Authorization") ?? "";
+    const algorithm = isQueryAuth ? url.searchParams.get("X-Amz-Algorithm") : authHeader.split(" ")[0];
+
+    if (!algorithm || !algorithm.includes("AWS4-HMAC-SHA256")) return false;
+
+    const datetime = (isQueryAuth ? url.searchParams.get("X-Amz-Date") : headers.get("x-amz-date")) ?? "";
+    const date = datetime.substring(0, 8);
+
+    const canonicalRequest = await createCanonicalRequest(request, isQueryAuth);
+    const hashedCanonicalRequest = await sha256(canonicalRequest);
+
+    const credentialScope = `${date}/${env.REGION}/s3/aws4_request`;
+    const stringToSign = ["AWS4-HMAC-SHA256", datetime, credentialScope, hashedCanonicalRequest].join("\n");
+
+    const signingKey = await getSigningKey(env.SECRET_KEY, date, env.REGION, "s3");
+    const signature = await hmacSha256(signingKey, stringToSign);
+    const signatureHex = bufToHex(signature);
+
+    let expectedSignature = "";
+    if (isQueryAuth) {
+        expectedSignature = url.searchParams.get("X-Amz-Signature") ?? "";
+    } else {
+        const match = authHeader.match(/Signature=([a-f0-9]+)/);
+        expectedSignature = match ? match[1] : "";
+    }
+
+    return signatureHex === expectedSignature;
+}
+
+async function createCanonicalRequest(request: Request, isQueryAuth: boolean): Promise<string> {
+    const url = new URL(request.url);
+
+    const searchParams = Array.from(url.searchParams.entries())
+        .filter(([key]) => key !== "X-Amz-Signature")
+        .sort(([a], [b]) => a.localeCompare(b))
+        .map(([key, val]) => `${encodeURIComponent(key)}=${encodeURIComponent(val)}`)
+        .join("&");
+
+    let signedHeadersList: string[] = [];
+    if (isQueryAuth) {
+        signedHeadersList = (url.searchParams.get("X-Amz-SignedHeaders") ?? "host").split(";");
+    } else {
+        const authHeader = request.headers.get("Authorization") ?? "";
+        const match = authHeader.match(/SignedHeaders=([^,]+)/);
+        signedHeadersList = match ? match[1].split(";") : ["host"];
+    }
+
+    const canonicalHeaders = signedHeadersList.map((h) => `${h}:${request.headers.get(h)?.trim() ?? ""}\n`).join("");
+
+    const signedHeaders = signedHeadersList.join(";");
+    const payloadHash = request.headers.get("x-amz-content-sha256") ?? "UNSIGNED-PAYLOAD";
+
+    return [request.method, url.pathname, searchParams, canonicalHeaders, signedHeaders, payloadHash].join("\n");
+}
+
+async function getSigningKey(secret: string, date: string, region: string, service: string): Promise<ArrayBuffer> {
+    const kDate = await hmacSha256("AWS4" + secret, date);
+    const kRegion = await hmacSha256(kDate, region);
+    const kService = await hmacSha256(kRegion, service);
+    return await hmacSha256(kService, "aws4_request");
+}
+
+async function hmacSha256(key: string | ArrayBuffer, data: string): Promise<ArrayBuffer> {
+    const keyData = typeof key === "string" ? new TextEncoder().encode(key) : key;
+    const cryptoKey = await crypto.subtle.importKey("raw", keyData, { name: "HMAC", hash: "SHA-256" }, false, ["sign"]);
+    return await crypto.subtle.sign("HMAC", cryptoKey, new TextEncoder().encode(data));
+}
+
+async function sha256(data: string): Promise<string> {
+    const hash = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(data));
+    return bufToHex(hash);
+}
+
+function bufToHex(buf: ArrayBuffer): string {
+    return Array.from(new Uint8Array(buf))
+        .map((b) => b.toString(16).padStart(2, "0"))
+        .join("");
+}