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>,