add link at bottom of page to import/export keys, add copy to clipboard buttons, adjust the How It Works section, add FAQ section

src/utils/crypto.ts

@@ -80,6 +80,11 @@ async function saveKeys(ecdhPublic: CryptoKey, ecdhPrivate: CryptoKey) {
   // Store ECDH key pair in local storage
   localStorage.setItem("ecdhPublic", JSON.stringify(ecdhPublicJwk));
   localStorage.setItem("ecdhPrivate", JSON.stringify(ecdhPrivateJwk));
+
+  return {
+    public: JSON.stringify(ecdhPublicJwk),
+    private: JSON.stringify(ecdhPrivateJwk),
+  };
 }
 
 export async function encrypt(
@@ -141,3 +146,57 @@ function base64ToUint8Array(base64: string): Uint8Array {
   }
   return bytes;
 }
+
+function downloadFile(content: string, fileName: string, contentType: string) {
+  const a = document.createElement("a");
+  const file = new Blob([content], { type: contentType });
+
+  a.href = URL.createObjectURL(file);
+  a.download = fileName;
+  a.click();
+
+  URL.revokeObjectURL(a.href);
+}
+
+export async function exportKeys(): Promise<void> {
+  const keys = await retrieveOrGenerateKeyPair();
+
+  const exportedKeys = await saveKeys(keys.publicKey, keys.privateKey);
+  const exportedKeysJson = JSON.stringify(exportedKeys);
+
+  downloadFile(exportedKeysJson, "keys.json", "application/json");
+}
+
+export async function importAndSaveKeys(keys: {
+  public: string;
+  private: string;
+}): Promise<void> {
+  const ecdhPublicJwk = JSON.parse(keys.public);
+  const ecdhPrivateJwk = JSON.parse(keys.private);
+
+  // Import the keys
+  const ecdhPublic = await window.crypto.subtle.importKey(
+    "jwk",
+    ecdhPublicJwk,
+    {
+      name: "ECDH",
+      namedCurve: "P-256",
+    },
+    true,
+    []
+  );
+
+  const ecdhPrivate = await window.crypto.subtle.importKey(
+    "jwk",
+    ecdhPrivateJwk,
+    {
+      name: "ECDH",
+      namedCurve: "P-256",
+    },
+    true,
+    ["deriveKey", "deriveBits"]
+  );
+
+  // Save the imported keys
+  saveKeys(ecdhPublic, ecdhPrivate);
+}