MbedAead::decrypt()

Summary: - implements ::decrypt, however doesn't support inplace encryption for now Reviewed By: kvtsoy Differential Revision: D49326635 fbshipit-source-id: fe52f347567b3cbafb62e2629e276ac4947adaab
facebook · Sep 22, 2023 · 83913c5 · 83913c5
1 parent 58d44aa
commit 83913c5
Show file tree

Hide file tree

Showing 2 changed files with 38 additions and 5 deletions.
diff --git a/quic/mbed/MbedAead.cpp b/quic/mbed/MbedAead.cpp
@@ -77,6 +77,40 @@ std::unique_ptr<folly::IOBuf> MbedAead::inplaceEncrypt(
   return ciphertext_buf;
 }
 
+folly::Optional<std::unique_ptr<folly::IOBuf>> MbedAead::tryDecrypt(
+    std::unique_ptr<folly::IOBuf>&& ciphertext,
+    const folly::IOBuf* assocData,
+    uint64_t seqNum) const {
+  // support only unchained iobufs for now
+  CHECK(!ciphertext->isChained());
+  CHECK(assocData == nullptr || !assocData->isChained());
+
+  setCipherKey(MBEDTLS_DECRYPT);
+
+  // create IOBuf of size len(plaintext) - getCipherOverhead()
+  const size_t tag_len = getCipherOverhead();
+  auto plaintext_buf = folly::IOBuf::create(ciphertext->length());
+  auto iv = getIV(seqNum);
+  size_t write_size{0};
+
+  if (mbedtls_cipher_auth_decrypt_ext(
+          /*ctx=*/&cipher_ctx,
+          /*iv=*/iv.data(),
+          /*iv_len=*/std::min<size_t>(iv.size(), key_.iv->length()),
+          /*ad=*/assocData ? assocData->data() : nullptr,
+          /*ad_len=*/assocData ? assocData->length() : 0,
+          /*input=*/ciphertext->data(),
+          /*ilen=*/ciphertext->length(),
+          /*output=*/plaintext_buf->writableData(),
+          /*output_len=*/plaintext_buf->capacity(),
+          /*olen=*/&write_size,
+          /*tag_len=*/tag_len) != 0) {
+    return folly::none;
+  }
+  plaintext_buf->append(write_size);
+  return plaintext_buf;
+}
+
 size_t MbedAead::getCipherOverhead() const {
   return TAG_LENGTH;
 }

diff --git a/quic/mbed/MbedAead.h b/quic/mbed/MbedAead.h
@@ -36,12 +36,11 @@ class MbedAead : public Aead {
       const folly::IOBuf* assocData,
       uint64_t seqNum) const override;
 
+  // does not support inplace decryption just yet
   folly::Optional<std::unique_ptr<folly::IOBuf>> tryDecrypt(
-      std::unique_ptr<folly::IOBuf>&& /*ciphertext*/,
-      const folly::IOBuf* /*associatedData*/,
-      uint64_t /*seqNum*/) const override {
-    return folly::none;
-  }
+      std::unique_ptr<folly::IOBuf>&& ciphertext,
+      const folly::IOBuf* assocData,
+      uint64_t seqNum) const override;
 
   // returns tag length
   size_t getCipherOverhead() const override;