PDF: throw on reads from an unauthenticated encrypted file

src/odr/exceptions.cpp

@@ -135,4 +135,8 @@ UnsupportedFileEncoding::UnsupportedFileEncoding(const std::string &message)
 FileEncryptedError::FileEncryptedError()
     : std::runtime_error("file encrypted error") {}
 
+UnauthenticatedReadError::UnauthenticatedReadError()
+    : std::runtime_error(
+          "cannot read encrypted object without authentication") {}
+
 } // namespace odr

src/odr/exceptions.hpp

@@ -230,4 +230,9 @@ struct FileEncryptedError final : std::runtime_error {
   explicit FileEncryptedError();
 };
 
+/// @brief Read attempted on an encrypted file that has not been authenticated
+struct UnauthenticatedReadError final : std::runtime_error {
+  explicit UnauthenticatedReadError();
+};
+
 } // namespace odr

src/odr/internal/pdf/pdf_document_parser.cpp

@@ -1,5 +1,6 @@
 #include <odr/internal/pdf/pdf_document_parser.hpp>
 
+#include <odr/exceptions.hpp>
 #include <odr/logger.hpp>
 
 #include <odr/internal/pdf/pdf_cmap_parser.hpp>
@@ -263,10 +264,7 @@ DocumentParser::DocumentParser(std::unique_ptr<std::istream> in,
 
   if (m_trailer.has_key("Encrypt")) {
     // Build an `Authenticator` from the trailer `/Encrypt` and `/ID`
-    // (ISO 32000-1 7.6). `m_is_encrypted` records that the file declares
-    // encryption regardless of whether we can authenticate it, so an
-    // unsupported handler still reports as encrypted.
-    m_is_encrypted = true;
+    // (ISO 32000-1 7.6).
 
     // The `/Encrypt` dictionary's own `/O`,`/U`,… strings are never encrypted
     // (7.6.2), and need no explicit self-skip guard: it is resolved here while
@@ -290,6 +288,12 @@ DocumentParser::DocumentParser(std::unique_ptr<std::istream> in,
       }
     }
 
+    // Set only after resolving `/Encrypt` above: `read_object` throws on an
+    // encrypted-but-unauthenticated read, and that resolution runs before any
+    // decryptor exists. `m_is_encrypted` records that the file declares
+    // encryption regardless of whether we can authenticate it, so an
+    // unsupported handler still reports as encrypted.
+    m_is_encrypted = true;
     m_authenticator = Authenticator::create(encrypt.as_dictionary(), id0);
   }
 
@@ -310,6 +314,10 @@ const Dictionary &DocumentParser::trailer() const { return m_trailer; }
 
 bool DocumentParser::is_encrypted() const { return m_is_encrypted; }
 
+bool DocumentParser::is_authenticated() const {
+  return m_is_encrypted && m_decryptor.has_value();
+}
+
 const std::optional<Authenticator> &DocumentParser::authenticator() const {
   return m_authenticator;
 }
@@ -350,6 +358,9 @@ DocumentParser::read_object(const ObjectReference &reference) {
     // case here: it is read and cached during construction before the
     // decryptor is installed, so its un-decrypted /O,/U,… strings are served
     // from the cache and never reach this path.
+    if (is_encrypted() && !is_authenticated()) {
+      throw UnauthenticatedReadError();
+    }
     if (m_decryptor.has_value()) {
       decrypt_strings(object.object, object.reference);
     }
@@ -422,6 +433,9 @@ std::string DocumentParser::read_object_stream(const IndirectObject &object) {
   // during the trailer-chain walk, before the decryptor exists, so they are
   // never decrypted (7.5.8.2); object streams are decrypted here as a whole,
   // leaving their members' plaintext.
+  if (is_encrypted() && !is_authenticated()) {
+    throw UnauthenticatedReadError();
+  }
   if (m_decryptor.has_value()) {
     raw = m_decryptor->decrypt_stream(object.reference, std::move(raw));
   }

src/odr/internal/pdf/pdf_document_parser.hpp

@@ -61,6 +61,9 @@ class DocumentParser {
 
   /// Whether the file declares an `/Encrypt` dictionary.
   [[nodiscard]] bool is_encrypted() const;
+  /// Whether the file is encrypted and a decryptor is installed, so reads can
+  /// decrypt. False for an encrypted file that has not been unlocked.
+  [[nodiscard]] bool is_authenticated() const;
   /// The authenticator for an encrypted file (validates passwords and produces
   /// a `Decryptor`), or `nullopt` if the file is not encrypted.
   [[nodiscard]] const std::optional<Authenticator> &authenticator() const;

test/src/internal/pdf/pdf_document_parser.cpp

@@ -1,3 +1,5 @@
+#include <odr/exceptions.hpp>
+
 #include <odr/internal/common/file.hpp>
 #include <odr/internal/pdf/pdf_document.hpp>
 #include <odr/internal/pdf/pdf_document_element.hpp>
@@ -147,6 +149,19 @@ TEST(DocumentParser, reopen_with_decryptor) {
   }
 }
 
+// Reading an encrypted file without authenticating must throw rather than serve
+// undecrypted bytes. The file reports as encrypted but not authenticated.
+TEST(DocumentParser, read_without_authentication_throws) {
+  const auto file = std::make_shared<DiskFile>(
+      TestData::test_file_path("odr-public/pdf/Casio_WVA-M650-7AJF.pdf"));
+
+  DocumentParser parser(file->stream());
+  EXPECT_TRUE(parser.is_encrypted());
+  EXPECT_FALSE(parser.is_authenticated());
+
+  EXPECT_THROW((void)parser.parse_document(), odr::UnauthenticatedReadError);
+}
+
 TEST(DocumentParser, inherited_page_attributes) {
   PdfFileBuilder builder;
   builder.object("<< /Type /Catalog /Pages 2 0 R >>")