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LibPDF: Implement 7.6.4.4.11 Algorithm 12: Authenticating owner password

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...for handlers of revision 6.

Since this adds U to the hash input, also trim the size of U and O to
48 bytes. The spec requires them to be 48 bytes, but all the newer PDFs
on https://cipa.jp/e/std/std-sec.html have 127 bytes -- 48 real bytes
and 79 nul padding bytes. These files were created by:

    Creator: Word 用 Acrobat PDFMaker 17
    Producer: Adobe PDF Library 15.0

and

    Creator: Word 用 Acrobat PDFMaker 17
    Producer: Adobe PDF Library 17.11.238
This commit is contained in:
Nico Weber 2023-07-19 21:03:47 -04:00 • committed by Andreas Kling
parent 8f6c67a71c
commit 57768325cc
2 changed files with 32 additions and 0 deletions
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31
Userland/Libraries/LibPDF/Encryption.cpp
View file

@ -166,6 +166,19 @@ PDFErrorOr<NonnullRefPtr<StandardSecurityHandler>> StandardSecurityHandler::crea
if (encryption_dict->contains(CommonNames::EncryptMetadata))
encryption_dict->get_value(CommonNames::EncryptMetadata).get<bool>();
if (v >= 5) {
// O and U are 48 bytes for V == 5, but some files pad them with nul bytes to 127 bytes. So trim them, if necessary.
if (o.length() > 48)
o = o.substring(0, 48);
if (u.length() > 48)
u = u.substring(0, 48);
if (o.length() != 48)
return Error(Error::Type::Parse, "Invalid O size");
if (u.length() != 48)
return Error(Error::Type::Parse, "Invalid U size");
}
return adopt_ref(*new StandardSecurityHandler(document, revision, o, u, p, encrypt_metadata, length, method));
}
@ -294,6 +307,24 @@ bool StandardSecurityHandler::authenticate_user_password_r6_and_later(StringView
return hash == m_u_entry.bytes().trim(32);
}
bool StandardSecurityHandler::authenticate_owner_password_r6_and_later(StringView password)
{
// ISO 32000 (PDF 2.0), 7.6.4.4.11 Algorithm 12: Authenticating the owner password (Security handlers of
// revision 6)
// a) Test the password against the owner key by computing the 32-byte hash using algorithm 2.B with an
// input string consisting of the UTF-8 password concatenated with the 8 bytes of Owner Validation Salt
// and the 48 byte U string. If the 32- byte result matches the first 32 bytes of the O string, this is the owner
// password.
ByteBuffer input;
input.append(password.bytes());
input.append(m_o_entry.bytes().slice(32, 8)); // See comment in compute_encryption_key_r6_and_later() re "Validation Salt".
input.append(m_u_entry.bytes());
auto hash = computing_a_hash_r6_and_later(input, password, HashKind::Owner);
return hash == m_o_entry.bytes().trim(32);
}
bool StandardSecurityHandler::try_provide_user_password(StringView password_string)
{
bool has_user_password;