diff --git a/fido/src/main/java/com/yubico/yubikit/fido/ctap/Hkdf.java b/fido/src/main/java/com/yubico/yubikit/fido/ctap/Hkdf.java
index 6e33e6b7..b75f2ff7 100644
--- a/fido/src/main/java/com/yubico/yubikit/fido/ctap/Hkdf.java
+++ b/fido/src/main/java/com/yubico/yubikit/fido/ctap/Hkdf.java
@@ -61,20 +61,29 @@ byte[] expand(byte[] prk, byte[] info, int length) throws InvalidKeyException {
                     .put(info)
                     .put(i)
                     .array();
-            t = hmacDigest(prk, data);
+            Arrays.fill(t, (byte) 0);
+            byte[] digest = hmacDigest(prk, data);
 
-            okm = ByteBuffer.allocate(okm.length + t.length)
+            byte[] result = ByteBuffer.allocate(okm.length + digest.length)
                     .put(okm)
-                    .put(t)
+                    .put(digest)
                     .array();
+            Arrays.fill(okm, (byte) 0);
+            Arrays.fill(data, (byte) 0);
+            okm = result;
+            t = digest;
         }
 
-        return Arrays.copyOf(okm, length);
+        byte[] result = Arrays.copyOf(okm, length);
+        Arrays.fill(okm, (byte) 0);
+        return result;
     }
 
     byte[] digest(byte[] ikm, byte[] salt, byte[] info, int length)
             throws NoSuchAlgorithmException, InvalidKeyException {
         byte[] prk = extract(salt, ikm);
-        return expand(prk, info, length);
+        byte[] result = expand(prk, info, length);
+        Arrays.fill(prk, (byte) 0);
+        return result;
     }
 }
diff --git a/fido/src/main/java/com/yubico/yubikit/fido/ctap/PinUvAuthProtocolV2.java b/fido/src/main/java/com/yubico/yubikit/fido/ctap/PinUvAuthProtocolV2.java
index a6cd0b3a..d35b3ac9 100644
--- a/fido/src/main/java/com/yubico/yubikit/fido/ctap/PinUvAuthProtocolV2.java
+++ b/fido/src/main/java/com/yubico/yubikit/fido/ctap/PinUvAuthProtocolV2.java
@@ -56,14 +56,16 @@ public int getVersion() {
 
     @Override
     public byte[] kdf(byte[] z) {
+        byte[] hmacKey = null;
+        byte[] aesKey = null;
         try {
-            byte[] hmacKey = new Hkdf(HKDF_ALG).digest(
+            hmacKey = new Hkdf(HKDF_ALG).digest(
                     z,
                     HKDF_SALT,
                     HKDF_INFO_HMAC,
                     HKDF_LENGTH);
 
-            byte[] aesKey = new Hkdf(HKDF_ALG).digest(
+            aesKey = new Hkdf(HKDF_ALG).digest(
                     z,
                     HKDF_SALT,
                     HKDF_INFO_AES,
@@ -75,13 +77,21 @@ public byte[] kdf(byte[] z) {
                     .array();
         } catch (NoSuchAlgorithmException | InvalidKeyException e) {
             throw new IllegalStateException(e);
+        } finally {
+            if (hmacKey != null) {
+                Arrays.fill(hmacKey, (byte) 0);
+            }
+            if (aesKey != null) {
+                Arrays.fill(aesKey, (byte) 0);
+            }
         }
     }
 
     @Override
     public byte[] encrypt(byte[] key, byte[] plaintext) {
+        byte[] aesKey = null;
         try {
-            byte[] aesKey = Arrays.copyOfRange(key, 32, key.length);
+            aesKey = Arrays.copyOfRange(key, 32, key.length);
             byte[] iv = RandomUtils.getRandomBytes(16);
 
             final byte[] ciphertext =
@@ -93,19 +103,27 @@ public byte[] encrypt(byte[] key, byte[] plaintext) {
                     .array();
         } catch (IllegalBlockSizeException | BadPaddingException e) {
             throw new IllegalStateException(e);
+        } finally {
+            if (aesKey != null) {
+                Arrays.fill(aesKey, (byte) 0);
+            }
         }
     }
 
     @Override
     public byte[] decrypt(byte[] key, byte[] ciphertext) {
+        byte[] aesKey = null;
         try {
-            byte[] aesKey = Arrays.copyOfRange(key, 32, key.length);
+            aesKey = Arrays.copyOfRange(key, 32, key.length);
             byte[] iv = Arrays.copyOf(ciphertext, 16);
             byte[] ct = Arrays.copyOfRange(ciphertext, 16, ciphertext.length);
-            byte[] plaintext = getCipher(Cipher.DECRYPT_MODE, aesKey, iv).doFinal(ct);
-            return Arrays.copyOf(plaintext, plaintext.length);
+            return getCipher(Cipher.DECRYPT_MODE, aesKey, iv).doFinal(ct);
         } catch (BadPaddingException | IllegalBlockSizeException e) {
             throw new IllegalStateException(e);
+        } finally {
+            if (aesKey != null) {
+                Arrays.fill(aesKey, (byte) 0);
+            }
         }
     }
 
@@ -120,8 +138,7 @@ public byte[] authenticate(byte[] key, byte[] message) {
         } catch (NoSuchAlgorithmException | InvalidKeyException e) {
             throw new RuntimeException(e);
         }
-        byte[] result = mac.doFinal(message);
-        return Arrays.copyOf(result, result.length);
+        return mac.doFinal(message);
     }
 
     private Cipher getCipher(int mode, byte[] secret, byte[] iv) {