🔒 Fix plaintext storage of credentials by implementing AES encryption

src/main/java/co/frenchpress/FileCredentialStore.java

@@ -1,10 +1,20 @@
 package co.frenchpress;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.attribute.PosixFilePermission;
+import java.security.SecureRandom;
+import java.util.Base64;
 import java.util.Set;
+import java.util.prefs.Preferences;
+import javax.crypto.Cipher;
+import javax.crypto.KeyGenerator;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.GCMParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
 
 /**
  * Default {@link CredentialStore}: a single file in a private directory,
@@ -24,7 +34,13 @@ public final class FileCredentialStore implements CredentialStore {
       Path p = path();
       if (!Files.isReadable(p)) return null;
       String s = Files.readString(p).strip();
-      return s.isEmpty() ? null : s;
+      if (s.isEmpty()) return null;
+      try {
+        return decrypt(s);
+      } catch (Exception e) {
+        // Fallback for legacy plaintext credentials
+        return s;
+      }
     } catch (Throwable t) {
       System.err.println("[frenchpress] credential load failed: " + t);
       return null;
@@ -40,7 +56,7 @@ public final class FileCredentialStore implements CredentialStore {
         trySetPerms(dir, Set.of(PosixFilePermission.OWNER_READ,
           PosixFilePermission.OWNER_WRITE, PosixFilePermission.OWNER_EXECUTE));
       }
-      Files.writeString(p, data);
+      Files.writeString(p, encrypt(data));
       trySetPerms(p, Set.of(PosixFilePermission.OWNER_READ,
         PosixFilePermission.OWNER_WRITE));
     } catch (Throwable t) {
@@ -60,6 +76,46 @@ private static void trySetPerms (Path p, Set<PosixFilePermission> perms) {
     }
   }
 
+  private static SecretKey getOrGenerateKey () throws Exception {
+    Preferences prefs = Preferences.userNodeForPackage(FileCredentialStore.class);
+    String encodedKey = prefs.get("frenchpress_aes_key", null);
+    if (encodedKey != null) {
+      byte[] decodedKey = Base64.getDecoder().decode(encodedKey);
+      return new SecretKeySpec(decodedKey, 0, decodedKey.length, "AES");
+    }
+    KeyGenerator keyGen = KeyGenerator.getInstance("AES");
+    keyGen.init(128);
+    SecretKey secretKey = keyGen.generateKey();
+    prefs.put("frenchpress_aes_key", Base64.getEncoder().encodeToString(secretKey.getEncoded()));
+    return secretKey;
+  }
+
+  private static String encrypt (String data) throws Exception {
+    SecretKey key = getOrGenerateKey();
+    Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
+    byte[] iv = new byte[12];
+    new SecureRandom().nextBytes(iv);
+    GCMParameterSpec parameterSpec = new GCMParameterSpec(128, iv);
+    cipher.init(Cipher.ENCRYPT_MODE, key, parameterSpec);
+    byte[] encryptedData = cipher.doFinal(data.getBytes(StandardCharsets.UTF_8));
+
+    ByteBuffer byteBuffer = ByteBuffer.allocate(iv.length + encryptedData.length);
+    byteBuffer.put(iv);
+    byteBuffer.put(encryptedData);
+    return Base64.getEncoder().encodeToString(byteBuffer.array());
+  }
+
+  private static String decrypt (String encryptedData) throws Exception {
+    SecretKey key = getOrGenerateKey();
+    byte[] cipherMessage = Base64.getDecoder().decode(encryptedData);
+
+    Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
+    GCMParameterSpec parameterSpec = new GCMParameterSpec(128, cipherMessage, 0, 12);
+    cipher.init(Cipher.DECRYPT_MODE, key, parameterSpec);
+    byte[] plainText = cipher.doFinal(cipherMessage, 12, cipherMessage.length - 12);
+    return new String(plainText, StandardCharsets.UTF_8);
+  }
+
   private static Path path () {
     String override = System.getenv("FRENCHPRESS_CRED_FILE");
     if (override != null && !override.isEmpty()) return Path.of(override);