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LibPDF: Treat Encyption's Length item as optional

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With the StandardSecurityHandler the Length item in the Encryption
dictionary is optional, and needs to be given only if the encryption
algorithm (V) is other than 1; otherwise we can assume a length of 40
bits for the encryption key.
This commit is contained in:
Rodrigo Tobar 2022-12-20 13:55:33 +08:00 • committed by Andreas Kling
parent b8dc05a08e
commit dc6a11cf6b
2 changed files with 16 additions and 1 deletions
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16
Userland/Libraries/LibPDF/Encryption.cpp
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@ -63,7 +63,21 @@ PDFErrorOr<NonnullRefPtr<StandardSecurityHandler>> StandardSecurityHandler::crea
auto o = TRY(encryption_dict->get_string(document, CommonNames::O))->string();
auto u = TRY(encryption_dict->get_string(document, CommonNames::U))->string();
auto p = encryption_dict->get_value(CommonNames::P).get<int>();
auto length = encryption_dict->get_value(CommonNames::Length).get<int>() / 8;
// V, number: [...] 1 "Algorithm 1 Encryption of data using the RC4 or AES algorithms" in 7.6.2,
// "General Encryption Algorithm," with an encryption key length of 40 bits, see below [...]
// Lenght, integer: (Optional; PDF 1.4; only if V is 2 or 3) The length of the encryption key, in bits.
// The value shall be a multiple of 8, in the range 40 to 128. Default value: 40.
int length_in_bits;
auto v = encryption_dict->get_value(CommonNames::V).get<int>();
if (encryption_dict->contains(CommonNames::Length))
length_in_bits = encryption_dict->get_value(CommonNames::Length).get<int>();
else if (v == 1)
length_in_bits = 40;
else
return Error(Error::Type::Parse, "Can't determine length of encryption key");
auto length = length_in_bits / 8;
bool encrypt_metadata = true;
if (encryption_dict->contains(CommonNames::EncryptMetadata))
encryption_dict->get_value(CommonNames::EncryptMetadata).get<bool>();