pw_crypto: Add SHA256 backed by Mbed TLS

Change-Id: I9ae84c9b3fff41129d1f6f17c2ee92d95078fa30
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/51061
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Ali Zhang <alizhang@google.com>

2 files changed, 45 insertions, 0 deletions

diff --git a/pw_crypto/public/pw_crypto/sha256.h b/pw_crypto/public/pw_crypto/sha256.h
index ef734a0df..9f1ccc9d2 100644
--- a/pw_crypto/public/pw_crypto/sha256.h
+++ b/pw_crypto/public/pw_crypto/sha256.h
@@ -17,6 +17,7 @@
 #include <cstdint>
 
 #include "pw_bytes/span.h"
+#include "pw_crypto/sha256_backend.h"
 #include "pw_status/status.h"
 
 namespace pw::crypto::sha256 {
@@ -28,6 +29,13 @@ constexpr uint32_t kDigestSizeBytes = 32;
 // messages.
 class Sha256 {
  public:
+  Sha256();
+  // Remove copy/move ctors
+  Sha256(const Sha256& other) = delete;
+  Sha256(Sha256&& other) = delete;
+  Sha256& operator=(const Sha256& other) = delete;
+  Sha256& operator=(Sha256&& other) = delete;
+
   // Update adds `data` to the running hasher.
   void Update(ConstByteSpan data);
 
diff --git a/pw_crypto/public/pw_crypto/sha256_mbedtls.h b/pw_crypto/public/pw_crypto/sha256_mbedtls.h
new file mode 100644
index 000000000..f77548b79
--- /dev/null
+++ b/pw_crypto/public/pw_crypto/sha256_mbedtls.h
@@ -0,0 +1,37 @@
+// Copyright 2021 The Pigweed Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#pragma once
+
+#include "mbedtls/md.h"
+
+namespace pw::crypto::sha256::backend {
+
+enum Sha256State {
+  // --> kInitialized upon construction, without fail.
+  kInitialized,
+  // kInitialized --> kStarted upon the first Update() call.
+  kStarted,
+  // kStarted --> kFinalized upon the first Final() call.
+  kFinalized,
+  // --> kError upon any unexpected failure.
+  kError,
+};
+
+struct Sha256Context {
+  Sha256State state;
+  mbedtls_md_context_t native_context;
+};
+
+}  // namespace pw::crypto::sha256::backend