diff --git a/confirmationui/1.0/default/PlatformSpecifics.cpp b/confirmationui/1.0/default/PlatformSpecifics.cpp
index dd039e2..03d6165 100644
--- a/confirmationui/1.0/default/PlatformSpecifics.cpp
+++ b/confirmationui/1.0/default/PlatformSpecifics.cpp
@@ -36,11 +36,11 @@
     }
 }
 
-support::NullOr<support::array<uint8_t, 32>> HMacImplementation::hmac256(
-    const uint8_t key[32], std::initializer_list<support::ByteBufferProxy> buffers) {
+support::NullOr<support::hmac_t> HMacImplementation::hmac256(
+    const support::auth_token_key_t& key, std::initializer_list<support::ByteBufferProxy> buffers) {
     HMAC_CTX hmacCtx;
     HMAC_CTX_init(&hmacCtx);
-    if (!HMAC_Init_ex(&hmacCtx, key, 32, EVP_sha256(), nullptr)) {
+    if (!HMAC_Init_ex(&hmacCtx, key.data(), key.size(), EVP_sha256(), nullptr)) {
         return {};
     }
     for (auto& buffer : buffers) {
@@ -48,7 +48,7 @@
             return {};
         }
     }
-    support::array<uint8_t, 32> result;
+    support::hmac_t result;
     if (!HMAC_Final(&hmacCtx, result.data(), nullptr)) {
         return {};
     }
diff --git a/confirmationui/1.0/default/PlatformSpecifics.h b/confirmationui/1.0/default/PlatformSpecifics.h
index 488da6d..29f299c 100644
--- a/confirmationui/1.0/default/PlatformSpecifics.h
+++ b/confirmationui/1.0/default/PlatformSpecifics.h
@@ -48,8 +48,9 @@
 
 class HMacImplementation {
    public:
-    static support::NullOr<support::array<uint8_t, 32>> hmac256(
-        const uint8_t key[32], std::initializer_list<support::ByteBufferProxy> buffers);
+    static support::NullOr<support::hmac_t> hmac256(
+        const support::auth_token_key_t& key,
+        std::initializer_list<support::ByteBufferProxy> buffers);
 };
 
 class MyOperation : public generic::Operation<sp<IConfirmationResultCallback>,
diff --git a/confirmationui/1.0/vts/functional/VtsHalConfirmationUIV1_0TargetTest.cpp b/confirmationui/1.0/vts/functional/VtsHalConfirmationUIV1_0TargetTest.cpp
index 463bb40..278d1f4 100644
--- a/confirmationui/1.0/vts/functional/VtsHalConfirmationUIV1_0TargetTest.cpp
+++ b/confirmationui/1.0/vts/functional/VtsHalConfirmationUIV1_0TargetTest.cpp
@@ -46,13 +46,16 @@
 
 namespace test {
 namespace {
+const support::auth_token_key_t testKey(static_cast<uint8_t>(TestKeyBits::BYTE));
+
 class HMacImplementation {
    public:
-    static support::NullOr<support::array<uint8_t, 32>> hmac256(
-        const uint8_t key[32], std::initializer_list<support::ByteBufferProxy> buffers) {
+    static support::NullOr<support::hmac_t> hmac256(
+        const support::auth_token_key_t& key,
+        std::initializer_list<support::ByteBufferProxy> buffers) {
         HMAC_CTX hmacCtx;
         HMAC_CTX_init(&hmacCtx);
-        if (!HMAC_Init_ex(&hmacCtx, key, 32, EVP_sha256(), nullptr)) {
+        if (!HMAC_Init_ex(&hmacCtx, key.data(), key.size(), EVP_sha256(), nullptr)) {
             return {};
         }
         for (auto& buffer : buffers) {
@@ -60,7 +63,7 @@
                 return {};
             }
         }
-        support::array<uint8_t, 32> result;
+        support::hmac_t result;
         if (!HMAC_Final(&hmacCtx, result.data(), nullptr)) {
             return {};
         }
@@ -70,23 +73,15 @@
 
 using HMacer = support::HMac<HMacImplementation>;
 
-constexpr uint8_t testKeyByte = static_cast<uint8_t>(TestKeyBits::BYTE);
-
 template <typename... Data>
 hidl_vec<uint8_t> testHMAC(const Data&... data) {
-    constexpr uint8_t testKey[32] = {testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                     testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                     testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                     testKeyByte, testKeyByte, testKeyByte, testKeyByte};
-    constexpr uint8_t hmac_size_bytes = sizeof testKey;
-
     auto hmac = HMacer::hmac256(testKey, data...);
     if (!hmac.isOk()) {
         EXPECT_TRUE(false) << "Failed to compute test hmac.  This is a self-test error.";
         return {};
     }
-    hidl_vec<uint8_t> result(hmac_size_bytes);
-    copy(hmac.value().data(), hmac.value().data() + hmac_size_bytes, result.data());
+    hidl_vec<uint8_t> result(hmac.value().size());
+    copy(hmac.value().data(), hmac.value().data() + hmac.value().size(), result.data());
     return result;
 }
 
diff --git a/confirmationui/support/include/android/hardware/confirmationui/1.0/generic/GenericOperation.h b/confirmationui/support/include/android/hardware/confirmationui/1.0/generic/GenericOperation.h
index b480942..b1c322c 100644
--- a/confirmationui/support/include/android/hardware/confirmationui/1.0/generic/GenericOperation.h
+++ b/confirmationui/support/include/android/hardware/confirmationui/1.0/generic/GenericOperation.h
@@ -99,7 +99,8 @@
 
     void setPending() { error_ = ResponseCode::OK; }
 
-    void setHmacKey(const uint8_t (&key)[32]) { hmacKey_ = {key}; }
+    void setHmacKey(const auth_token_key_t& key) { hmacKey_ = key; }
+    NullOr<auth_token_key_t> hmacKey() const { return hmacKey_; }
 
     void abort() {
         if (isPending()) {
@@ -112,7 +113,7 @@
         if (isPending()) error_ = ResponseCode::Canceled;
     }
 
-    void finalize(const uint8_t key[32]) {
+    void finalize(const auth_token_key_t& key) {
         if (error_ == ResponseCode::Ignored) return;
         resultCB_->result(error_, getMessage(), userConfirm(key));
         error_ = ResponseCode::Ignored;
@@ -127,11 +128,7 @@
     }
 
     ResponseCode deliverSecureInputEvent(const HardwareAuthToken& secureInputToken) {
-        constexpr uint8_t testKeyByte = static_cast<uint8_t>(TestKeyBits::BYTE);
-        constexpr uint8_t testKey[32] = {testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                         testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                         testKeyByte, testKeyByte, testKeyByte, testKeyByte,
-                                         testKeyByte, testKeyByte, testKeyByte, testKeyByte};
+        const auth_token_key_t testKey(static_cast<uint8_t>(TestKeyBits::BYTE));
 
         auto hmac = HMacer::hmac256(testKey, "\0", bytes_cast(secureInputToken.challenge),
                                     bytes_cast(secureInputToken.userId),
@@ -171,7 +168,7 @@
         result.setToExternal(formattedMessageBuffer_, formattedMessageLength_);
         return result;
     }
-    hidl_vec<uint8_t> userConfirm(const uint8_t key[32]) {
+    hidl_vec<uint8_t> userConfirm(const auth_token_key_t& key) {
         if (error_ != ResponseCode::OK) return {};
         confirmationTokenScratchpad_ = HMacer::hmac256(key, "confirmation token", getMessage());
         if (!confirmationTokenScratchpad_.isOk()) {
@@ -188,10 +185,10 @@
     uint8_t formattedMessageBuffer_[uint32_t(MessageSize::MAX)];
     char promptStringBuffer_[uint32_t(MessageSize::MAX)];
     size_t formattedMessageLength_ = 0;
-    NullOr<array<uint8_t, 32>> confirmationTokenScratchpad_;
+    NullOr<hmac_t> confirmationTokenScratchpad_;
     Callback resultCB_;
     typename TimeStamper::TimeStamp startTime_;
-    NullOr<array<uint8_t, 32>> hmacKey_;
+    NullOr<auth_token_key_t> hmacKey_;
 };
 
 }  // namespace
diff --git a/confirmationui/support/include/android/hardware/confirmationui/support/confirmationui_utils.h b/confirmationui/support/include/android/hardware/confirmationui/support/confirmationui_utils.h
index d551433..3f7810a 100644
--- a/confirmationui/support/include/android/hardware/confirmationui/support/confirmationui_utils.h
+++ b/confirmationui/support/include/android/hardware/confirmationui/support/confirmationui_utils.h
@@ -81,17 +81,23 @@
    public:
     array() : data_{} {}
     array(const T (&data)[elements]) { std::copy(data, data + elements, data_); }
+    explicit array(const T& v) { fill(v); }
 
     T* data() { return data_; }
     const T* data() const { return data_; }
     constexpr size_t size() const { return elements; }
-    operator const array_type&() const { return data_; }
 
     T* begin() { return data_; }
     T* end() { return data_ + elements; }
     const T* begin() const { return data_; }
     const T* end() const { return data_ + elements; }
 
+    void fill(const T& v) {
+        for (size_t i = 0; i < elements; ++i) {
+            data_[i] = v;
+        }
+    }
+
    private:
     array_type data_;
 };
@@ -157,6 +163,11 @@
     size_t size_;
 };
 
+constexpr uint8_t auth_token_key_size = 32;
+constexpr uint8_t hmac_size_bytes = support::auth_token_key_size;
+using auth_token_key_t = array<uint8_t, auth_token_key_size>;
+using hmac_t = auth_token_key_t;
+
 /**
  * Implementer are expected to provide an implementation with the following prototype:
  *  static NullOr<array<uint8_t, 32>> hmac256(const uint8_t key[32],
@@ -166,7 +177,7 @@
 class HMac {
    public:
     template <typename... Data>
-    static NullOr<array<uint8_t, 32>> hmac256(const uint8_t key[32], const Data&... data) {
+    static NullOr<hmac_t> hmac256(const auth_token_key_t& key, const Data&... data) {
         return Impl::hmac256(key, {data...});
     }
 };