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LibPDF: Simplify AESV2 code a bit

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- `encrypt()` will always fill a multiple of block size,
  `decrypt()` might produce less data. But other than that,
  the middle span isn't modified even though it's a reference.
  So pass the ByteBuffer to assign() (kind of like before 5998072f15,
  but pass-by-move())

- In the encryption code path, assign a single buffer for IV and data
  instead of awkwardly copying the data around later.

Thanks to CxByte for suggesting most of this!

No intentional behavior change.
This commit is contained in:
Nico Weber 2023-07-17 18:56:59 -04:00 • committed by Andreas Kling
parent e5bcd6c731
commit 7a48d59727
1 changed files with 14 additions and 17 deletions
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31
Userland/Libraries/LibPDF/Encryption.cpp
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@ -518,14 +518,14 @@ void StandardSecurityHandler::crypt(NonnullRefPtr<Object> object, Reference refe
auto encryption_key = m_encryption_key.value();
ReadonlyBytes bytes;
Function<void(ReadonlyBytes)> assign;
Function<void(ByteBuffer)> assign;
if (object->is<StreamObject>()) {
auto stream = object->cast<StreamObject>();
bytes = stream->bytes();
assign = [&object](ReadonlyBytes bytes) {
object->cast<StreamObject>()->buffer() = MUST(ByteBuffer::copy(bytes));
assign = [&object](ByteBuffer buffer) {
object->cast<StreamObject>()->buffer() = move(buffer);
};
if (stream->dict()->contains(CommonNames::Filter)) {
@ -536,8 +536,8 @@ void StandardSecurityHandler::crypt(NonnullRefPtr<Object> object, Reference refe
} else if (object->is<StringObject>()) {
auto string = object->cast<StringObject>();
bytes = string->string().bytes();
assign = [&object](ReadonlyBytes bytes) {
object->cast<StringObject>()->set_string(DeprecatedString(bytes));
assign = [&object](ByteBuffer buffer) {
object->cast<StringObject>()->set_string(DeprecatedString(buffer.bytes()));
};
} else {
VERIFY_NOT_REACHED();
@ -579,18 +579,14 @@ void StandardSecurityHandler::crypt(NonnullRefPtr<Object> object, Reference refe
// that is stored as the first 16 bytes of the encrypted stream or string."
static_assert(Crypto::Cipher::AESCipher::block_size() == 16);
if (direction == Crypto::Cipher::Intent::Encryption) {
auto encrypted = MUST(cipher.create_aligned_buffer(bytes.size()));
auto encrypted_span = encrypted.bytes();
auto output = MUST(cipher.create_aligned_buffer(16 + bytes.size()));
auto iv_span = output.bytes().trim(16);
auto encrypted_span = output.bytes().slice(16);
auto iv = MUST(ByteBuffer::create_uninitialized(Crypto::Cipher::AESCipher::block_size()));
fill_with_random(iv);
fill_with_random(iv_span);
cipher.encrypt(bytes, encrypted_span, iv_span);
cipher.encrypt(bytes, encrypted_span, iv);
ByteBuffer output;
output.append(iv);
output.append(encrypted_span);
assign(output);
assign(move(output));
} else {
VERIFY(direction == Crypto::Cipher::Intent::Decryption);
@ -600,8 +596,9 @@ void StandardSecurityHandler::crypt(NonnullRefPtr<Object> object, Reference refe
auto decrypted = MUST(cipher.create_aligned_buffer(bytes.size()));
auto decrypted_span = decrypted.bytes();
cipher.decrypt(bytes, decrypted_span, iv);
decrypted.resize(decrypted_span.size());
assign(decrypted_span);
assign(move(decrypted));
}
return;
@ -612,7 +609,7 @@ void StandardSecurityHandler::crypt(NonnullRefPtr<Object> object, Reference refe
RC4 rc4(key);
auto output = rc4.encrypt(bytes);
assign(output);
assign(move(output));
}
void StandardSecurityHandler::encrypt(NonnullRefPtr<Object> object, Reference reference) const