commit 472287f5734c1f4e5092f6bc2d34e3a2d14d3f94
author Ali Zhang <alizhang@google.com> Fri Jul 16 16:09:31 2021 -0700
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Sat Jul 31 01:11:12 2021 +0000
tree 5a6c32e2006120b2076bd2c37d58aa45ddee77c1
parent 4947e7781dc13928ac38e0f9893732213a29d7af

pw_crypto: Use mbedtls_sha256_* directly

Use the mbedtls_sha256_* APIs instead of the more general mbedtls_md_*
for an immediate reduction in code size -- 19KiB --> 2.8KiB. This avoids
the need to configure Mbed TLS to remove unused hashing algorithms
supported by mbedtls_md_*.

No-Docs-Update-Reason: no behavioral changes.
Change-Id: I7d450e6cb102aa395daabc20a98d1f0ca56360c0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/53540
Reviewed-by: Darren Krahn <dkrahn@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Ali Zhang <alizhang@google.com>

pw_crypto/public/pw_crypto/sha256_mbedtls.h

diff --git a/pw_crypto/public/pw_crypto/sha256_mbedtls.h b/pw_crypto/public/pw_crypto/sha256_mbedtls.h
index f77548b..dfb38fa 100644
--- a/pw_crypto/public/pw_crypto/sha256_mbedtls.h
+++ b/pw_crypto/public/pw_crypto/sha256_mbedtls.h
@@ -14,24 +14,22 @@
 
 #pragma once
 
-#include "mbedtls/md.h"
+#include "mbedtls/sha256.h"
 
 namespace pw::crypto::sha256::backend {
 
 enum Sha256State {
-  // --> kInitialized upon construction, without fail.
+  // Successfully initialized (during contruction).
   kInitialized,
-  // kInitialized --> kStarted upon the first Update() call.
-  kStarted,
-  // kStarted --> kFinalized upon the first Final() call.
+  // Finalized as a result of the first Final() call.
   kFinalized,
-  // --> kError upon any unexpected failure.
+  // Invalid/unrecoverable state.
   kError,
 };
 
 struct Sha256Context {
   Sha256State state;
-  mbedtls_md_context_t native_context;
+  mbedtls_sha256_context native_context;
 };
 
 }  // namespace pw::crypto::sha256::backend

pw_crypto/sha256_mbedtls.cc

diff --git a/pw_crypto/sha256_mbedtls.cc b/pw_crypto/sha256_mbedtls.cc
index 6db13cd..670fa95 100644
--- a/pw_crypto/sha256_mbedtls.cc
+++ b/pw_crypto/sha256_mbedtls.cc
@@ -18,35 +18,24 @@
 namespace pw::crypto::sha256 {
 
 Sha256::Sha256() {
-  // mbedtsl_md_init() never fails (returns void).
-  mbedtls_md_init(&ctx_.native_context);
+  // mbedtsl_sha256_init() never fails (returns void).
+  mbedtls_sha256_init(&ctx_.native_context);
+
   ctx_.state = backend::Sha256State::kInitialized;
+  if (mbedtls_sha256_starts_ret(&ctx_.native_context, /* is224 = */ 0)) {
+    ctx_.state = backend::Sha256State::kError;
+  }
 }
 
 void Sha256::Update(ConstByteSpan data) {
-  if (ctx_.state == backend::Sha256State::kInitialized) {
-    if (mbedtls_md_setup(&ctx_.native_context,
-                         mbedtls_md_info_from_type(MBEDTLS_MD_SHA256),
-                         /* hmac = */ 0)) {
-      ctx_.state = backend::Sha256State::kError;
-      return;
-    }
-
-    if (mbedtls_md_starts(&ctx_.native_context)) {
-      ctx_.state = backend::Sha256State::kError;
-      return;
-    }
-
-    ctx_.state = backend::Sha256State::kStarted;
-  }
-
-  if (ctx_.state != backend::Sha256State::kStarted) {
+  if (ctx_.state != backend::Sha256State::kInitialized) {
     return;
   }
 
-  if (mbedtls_md_update(&ctx_.native_context,
-                        reinterpret_cast<const unsigned char*>(data.data()),
-                        data.size())) {
+  if (mbedtls_sha256_update_ret(
+          &ctx_.native_context,
+          reinterpret_cast<const unsigned char*>(data.data()),
+          data.size())) {
     ctx_.state = backend::Sha256State::kError;
     return;
   }
@@ -60,17 +49,13 @@
     return Status::InvalidArgument();
   }
 
-  if (ctx_.state == backend::Sha256State::kInitialized) {
-    // It is OK for users to forget or skip Update().
-    Update({});
-  }
-
-  if (ctx_.state != backend::Sha256State::kStarted) {
+  if (ctx_.state != backend::Sha256State::kInitialized) {
     return Status::FailedPrecondition();
   }
 
-  if (mbedtls_md_finish(&ctx_.native_context,
-                        reinterpret_cast<unsigned char*>(out_digest.data()))) {
+  if (mbedtls_sha256_finish_ret(
+          &ctx_.native_context,
+          reinterpret_cast<unsigned char*>(out_digest.data()))) {
     ctx_.state = backend::Sha256State::kError;
     return Status::Internal();
   }