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PDF4QT/PdfForQtLib/sources/pdfsecurityhandler.cpp

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// Copyright (C) 2019-2020 Jakub Melka
//
// This file is part of PdfForQt.
//
// PdfForQt is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// PdfForQt is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with PDFForQt. If not, see <https://www.gnu.org/licenses/>.
#include "pdfsecurityhandler.h"
#include "pdfexception.h"
#include "pdfencoding.h"
#include "pdfvisitor.h"
#include "pdfutils.h"
#include <openssl/rc4.h>
#include <openssl/md5.h>
#include <openssl/aes.h>
#include <openssl/sha.h>
#include <array>
namespace pdf
{
// Padding password
static constexpr std::array<uint8_t, 32> PDFPasswordPadding = {
0x28, 0xBF, 0x4E, 0x5E, 0x4E, 0x75, 0x8A, 0x41,
0x64, 0x00, 0x4E, 0x56, 0xFF, 0xFA, 0x01, 0x08,
0x2E, 0x2E, 0x00, 0xB6, 0xD0, 0x68, 0x3E, 0x80,
0x2F, 0x0C, 0xA9, 0xFE, 0x64, 0x53, 0x69, 0x7A
};
class PDFDecryptObjectVisitor : public PDFAbstractVisitor
{
public:
explicit PDFDecryptObjectVisitor(const PDFSecurityHandler* securityHandler, PDFObjectReference reference) :
m_securityHandler(securityHandler),
m_reference(reference)
{
m_objectStack.reserve(32);
}
virtual void visitNull() override;
virtual void visitBool(bool value) override;
virtual void visitInt(PDFInteger value) override;
virtual void visitReal(PDFReal value) override;
virtual void visitString(PDFStringRef string) override;
virtual void visitName(PDFStringRef name) override;
virtual void visitArray(const PDFArray* array) override;
virtual void visitDictionary(const PDFDictionary* dictionary) override;
virtual void visitStream(const PDFStream* stream) override;
virtual void visitReference(const PDFObjectReference reference) override;
PDFObject getDecryptedObject();
private:
const PDFSecurityHandler* m_securityHandler;
std::vector<PDFObject> m_objectStack;
PDFObjectReference m_reference;
};
void PDFDecryptObjectVisitor::visitNull()
{
m_objectStack.push_back(PDFObject::createNull());
}
void PDFDecryptObjectVisitor::visitBool(bool value)
{
m_objectStack.push_back(PDFObject::createBool(value));
}
void PDFDecryptObjectVisitor::visitInt(PDFInteger value)
{
m_objectStack.push_back(PDFObject::createInteger(value));
}
void PDFDecryptObjectVisitor::visitReal(PDFReal value)
{
m_objectStack.push_back(PDFObject::createReal(value));
}
void PDFDecryptObjectVisitor::visitString(PDFStringRef string)
{
m_objectStack.push_back(PDFObject::createString(m_securityHandler->decrypt(string.getString(), m_reference, PDFSecurityHandler::EncryptionScope::String)));
}
void PDFDecryptObjectVisitor::visitName(PDFStringRef name)
{
m_objectStack.push_back(PDFObject::createName(name));
}
void PDFDecryptObjectVisitor::visitArray(const PDFArray* array)
{
acceptArray(array);
// We have all objects on the stack
Q_ASSERT(array->getCount() <= m_objectStack.size());
auto it = std::next(m_objectStack.cbegin(), m_objectStack.size() - array->getCount());
std::vector<PDFObject> objects(it, m_objectStack.cend());
PDFObject object = PDFObject::createArray(std::make_shared<PDFArray>(qMove(objects)));
m_objectStack.erase(it, m_objectStack.cend());
m_objectStack.push_back(object);
}
void PDFDecryptObjectVisitor::visitDictionary(const PDFDictionary* dictionary)
{
Q_ASSERT(dictionary);
// We must check, if it is or isn't a signature dictionary. If it is,
// then don't decrypt the Content value. We also don't check, if signature
// isn't indirectly referenced by reference. Hope it isn't...
const PDFObject& typeObject = dictionary->get("Type");
bool isSignatureObject = (typeObject.isName() && typeObject.getString() == "Sig");
std::vector<PDFDictionary::DictionaryEntry> entries;
entries.reserve(dictionary->getCount());
for (size_t i = 0, count = dictionary->getCount(); i < count; ++i)
{
if (isSignatureObject && dictionary->getKey(i) == "Contents")
{
entries.emplace_back(dictionary->getKey(i), dictionary->getValue(i));
}
else
{
dictionary->getValue(i).accept(this);
entries.emplace_back(dictionary->getKey(i), m_objectStack.back());
m_objectStack.pop_back();
}
}
m_objectStack.push_back(PDFObject::createDictionary(std::make_shared<PDFDictionary>(qMove(entries))));
}
void PDFDecryptObjectVisitor::visitStream(const PDFStream* stream)
{
// Don't decrypt, if it is a Metadata stream and Metadata encryption is turned off
const PDFDictionary* dictionary = stream->getDictionary();
const PDFObject& typeObject = dictionary->get("Type");
bool isMetadata = (typeObject.isName() && typeObject.getString() == "Metadata");
if (isMetadata && !m_securityHandler->isMetadataEncrypted())
{
m_objectStack.push_back(PDFObject::createStream(std::make_shared<PDFStream>(PDFDictionary(*dictionary), QByteArray(*stream->getContent()))));
return;
}
// Decrypt the dictionary
visitDictionary(dictionary);
PDFObject dictionaryObject = m_objectStack.back();
m_objectStack.pop_back();
// We must also handle situation, that stream has specified Crypt filter.
// In this case, we must delegate decryption to the stream filters.
PDFDictionary decryptedDictionary(*dictionaryObject.getDictionary());
QByteArray decryptedData;
if (!decryptedDictionary.hasKey("Crypt"))
{
decryptedData = m_securityHandler->decrypt(*stream->getContent(), m_reference, PDFSecurityHandler::EncryptionScope::Stream);
}
else
{
decryptedData = *stream->getContent();
decryptedDictionary.addEntry(PDFInplaceOrMemoryString(PDFSecurityHandler::OBJECT_REFERENCE_DICTIONARY_NAME), PDFObject::createReference(m_reference));
}
m_objectStack.push_back(PDFObject::createStream(std::make_shared<PDFStream>(qMove(decryptedDictionary), qMove(decryptedData))));
}
void PDFDecryptObjectVisitor::visitReference(const PDFObjectReference reference)
{
m_objectStack.push_back(PDFObject::createReference(reference));
}
PDFObject PDFDecryptObjectVisitor::getDecryptedObject()
{
Q_ASSERT(m_objectStack.size() == 1);
return qMove(m_objectStack.back());
}
PDFObject PDFSecurityHandler::decryptObject(const PDFObject& object, PDFObjectReference reference) const
{
PDFDecryptObjectVisitor visitor(this, reference);
object.accept(&visitor);
return visitor.getDecryptedObject();
}
PDFSecurityHandlerPointer PDFSecurityHandler::createSecurityHandler(const PDFObject& encryptionDictionaryObject, const QByteArray& id)
{
if (encryptionDictionaryObject.isNull())
{
return PDFSecurityHandlerPointer(new PDFNoneSecurityHandler());
}
if (!encryptionDictionaryObject.isDictionary())
{
throw PDFException(PDFTranslationContext::tr("Invalid encryption dictionary."));
}
const PDFDictionary* dictionary = encryptionDictionaryObject.getDictionary();
auto getName = [](const PDFDictionary* dictionary, const char* key, bool required, const char* defaultValue = nullptr) -> QByteArray
{
const PDFObject& nameObject = dictionary->get(key);
if (nameObject.isNull())
{
return defaultValue ? QByteArray(defaultValue) : QByteArray();
}
if (!nameObject.isName())
{
if (required)
{
throw PDFException(PDFTranslationContext::tr("Invalid value for entry '%1' in encryption dictionary. Name expected.").arg(QString::fromLatin1(key)));
}
return defaultValue ? QByteArray(defaultValue) : QByteArray();
}
return nameObject.getString();
};
auto getInt = [](const PDFDictionary* dictionary, const char* key, bool required, PDFInteger defaultValue = -1) -> PDFInteger
{
const PDFObject& intObject = dictionary->get(key);
if (!intObject.isInt())
{
if (required)
{
throw PDFException(PDFTranslationContext::tr("Invalid value for entry '%1' in encryption dictionary. Integer expected.").arg(QString::fromLatin1(key)));
}
return defaultValue;
}
return intObject.getInteger();
};
QByteArray filterName = getName(dictionary, "Filter", true);
if (filterName != "Standard")
{
throw PDFException(PDFTranslationContext::tr("Unknown security handler."));
}
const int V = getInt(dictionary, "V", true);
// Check V
if (V < 1 || V > 5)
{
throw PDFException(PDFTranslationContext::tr("Unsupported version of document encryption (V = %1).").arg(V));
}
// Only valid for V == 2 or V == 3, otherwise we set file encryption key length manually
int Length = 40;
switch (V)
{
case 1:
Length = 40;
break;
case 2:
case 3:
Length = getInt(dictionary, "Length", false, 40);
break;
case 4:
Length = 128;
break;
case 5:
Length = 256;
break;
default:
Q_ASSERT(false);
break;
}
// Create standard security handler
PDFStandardSecurityHandler handler;
handler.m_V = V;
handler.m_keyLength = Length;
// Add "Identity" filter to the filters
CryptFilter identityFilter;
identityFilter.type = CryptFilterType::Identity;
handler.m_cryptFilters[IDENTITY_FILTER_NAME] = identityFilter;
if (V == 4 || V == 5)
{
const PDFObject& cryptFilterObjects = dictionary->get("CF");
if (cryptFilterObjects.isDictionary())
{
auto parseCryptFilter = [Length, &getName, &getInt](const PDFObject& object) -> CryptFilter
{
if (!object.isDictionary())
{
throw PDFException(PDFTranslationContext::tr("Crypt filter is not a dictionary!"));
}
const PDFDictionary* cryptFilterDictionary = object.getDictionary();
CryptFilter filter;
QByteArray CFMName = getName(cryptFilterDictionary, "CFM", false, "None");
if (CFMName == "None")
{
filter.type = CryptFilterType::None;
}
else if (CFMName == "V2")
{
filter.type = CryptFilterType::V2;
}
else if (CFMName == "AESV2")
{
filter.type = CryptFilterType::AESV2;
}
else if (CFMName == "AESV3")
{
filter.type = CryptFilterType::AESV3;
}
else
{
throw PDFException(PDFTranslationContext::tr("Unsupported encryption algorithm '%1'.").arg(QString::fromLatin1(CFMName)));
}
QByteArray authEventName = getName(cryptFilterDictionary, "AuthEvent", false, "DocOpen");
if (authEventName == "DocOpen")
{
filter.authEvent = AuthEvent::DocOpen;
}
else if (authEventName == "EFOpen")
{
filter.authEvent = AuthEvent::EFOpen;
}
else
{
throw PDFException(PDFTranslationContext::tr("Unsupported authorization event '%1'.").arg(QString::fromLatin1(authEventName)));
}
filter.keyLength = getInt(cryptFilterDictionary, "Length", false, Length / 8);
return filter;
};
const PDFDictionary* cryptFilters = cryptFilterObjects.getDictionary();
for (size_t i = 0, cryptFilterCount = cryptFilters->getCount(); i < cryptFilterCount; ++i)
{
handler.m_cryptFilters[cryptFilters->getKey(i).getString()] = parseCryptFilter(cryptFilters->getValue(i));
}
}
// Now, add standard filters
auto resolveFilter = [&handler](const QByteArray& name)
{
auto it = handler.m_cryptFilters.find(name);
if (it == handler.m_cryptFilters.cend())
{
throw PDFException(PDFTranslationContext::tr("Uknown crypt filter '%1'.").arg(QString::fromLatin1(name)));
}
return it->second;
};
handler.m_filterStreams = resolveFilter(getName(dictionary, "StmF", false, IDENTITY_FILTER_NAME));
handler.m_filterStrings = resolveFilter(getName(dictionary, "StrF", false, IDENTITY_FILTER_NAME));
if (dictionary->hasKey("EFF"))
{
handler.m_filterEmbeddedFiles = resolveFilter(getName(dictionary, "EFF", true));
}
else
{
// According to the PDF specification, if 'EFF' entry is omitted, then filter
// for streams is used.
handler.m_filterEmbeddedFiles = handler.m_filterStreams;
}
}
int R = getInt(dictionary, "R", true);
if (R < 2 || R > 6)
{
throw PDFException(PDFTranslationContext::tr("Revision %1 of standard security handler is not supported.").arg(R));
}
handler.m_R = R;
handler.m_filterDefault.authEvent = AuthEvent::DocOpen;
handler.m_filterDefault.keyLength = Length / 8;
handler.m_filterDefault.type = (R > 4) ? CryptFilterType::AESV3 : CryptFilterType::V2;
auto readByteArray = [dictionary](const char* key, int size)
{
QByteArray result;
const PDFObject& object = dictionary->get(key);
if (object.isString())
{
result = object.getString();
if (result.size() != size)
{
throw PDFException(PDFTranslationContext::tr("Expected %1 characters long string in entry '%2'. Provided length is %3.").arg(size).arg(QString::fromLatin1(key)).arg(result.size()));
}
}
else
{
throw PDFException(PDFTranslationContext::tr("Expected %1 characters long string in entry '%2'.").arg(size).arg(QString::fromLatin1(key)));
}
return result;
};
handler.m_O = readByteArray("O", (R != 6 && R != 5) ? 32 : 48);
handler.m_U = readByteArray("U", (R != 6 && R != 5) ? 32 : 48);
handler.m_permissions = static_cast<uint32_t>(static_cast<int>(getInt(dictionary, "P", true)));
if (R == 6 || R == 5)
{
handler.m_OE = readByteArray("OE", 32);
handler.m_UE = readByteArray("UE", 32);
handler.m_Perms = readByteArray("Perms", 16);
}
const PDFObject& encryptMetadataObject = dictionary->get("EncryptMetadata");
if (encryptMetadataObject.isBool())
{
handler.m_encryptMetadata = encryptMetadataObject.getBool();
}
handler.m_ID = id;
return PDFSecurityHandlerPointer(new PDFStandardSecurityHandler(qMove(handler)));
}
PDFSecurityHandler::AuthorizationResult PDFStandardSecurityHandler::authenticate(const std::function<QString(bool*)>& getPasswordCallback)
{
QByteArray password;
bool passwordObtained = true;
// Clear the authorization data
m_authorizationData = AuthorizationData();
while (passwordObtained)
{
switch (m_R)
{
case 2:
case 3:
case 4:
{
// Try to authorize by owner password
{
QByteArray userPassword = createUserPasswordFromOwnerPassword(password);
QByteArray fileEncryptionKey = createFileEncryptionKey(userPassword);
QByteArray U = createEntryValueU_r234(fileEncryptionKey);
if (U == m_U)
{
// We have authorized owner access
m_authorizationData.authorizationResult = AuthorizationResult::OwnerAuthorized;
m_authorizationData.fileEncryptionKey = fileEncryptionKey;
return AuthorizationResult::OwnerAuthorized;
}
}
// Try to authorize user password
QByteArray fileEncryptionKey = createFileEncryptionKey(password);
QByteArray U = createEntryValueU_r234(fileEncryptionKey);
if (U == m_U)
{
// We have authorized owner access
m_authorizationData.authorizationResult = AuthorizationResult::UserAuthorized;
m_authorizationData.fileEncryptionKey = fileEncryptionKey;
return AuthorizationResult::UserAuthorized;
}
break;
}
case 5:
case 6:
{
UserOwnerData_r6 userData = parseParts(m_U);
UserOwnerData_r6 ownerData = parseParts(m_O);
auto createHash_r5 = [](const QByteArray& inputData)
{
QByteArray result(SHA256_DIGEST_LENGTH, char(0));
SHA256(convertByteArrayToUcharPtr(inputData), inputData.size(), convertByteArrayToUcharPtr(result));
return result;
};
auto createHash_r56 = [this, &createHash_r5](const QByteArray& input, const QByteArray& inputPassword, bool useUserKey)
{
return (m_R == 5) ? createHash_r5(input) : createHash_r6(input, inputPassword, useUserKey);
};
// Try to authorize owner password
{
QByteArray inputData = password + ownerData.validationSalt + m_U;
QByteArray hash = createHash_r56(inputData, password, true);
if (hash == ownerData.hash)
{
// We have authorized owner access. Now we must calculate the owner encryption key
QByteArray fileEncryptionKeyInputData = password + ownerData.keySalt + m_U;
QByteArray fileEncryptionDecryptionKey = createHash_r56(fileEncryptionKeyInputData, password, true);
Q_ASSERT(fileEncryptionDecryptionKey.size() == 32);
AES_KEY key = { };
AES_set_decrypt_key(convertByteArrayToUcharPtr(fileEncryptionDecryptionKey), fileEncryptionDecryptionKey.size() * 8, &key);
unsigned char aesInitializationVector[AES_BLOCK_SIZE] = { };
m_authorizationData.fileEncryptionKey.resize(m_OE.size());
AES_cbc_encrypt(convertByteArrayToUcharPtr(m_OE), convertByteArrayToUcharPtr(m_authorizationData.fileEncryptionKey), m_OE.size(), &key, aesInitializationVector, AES_DECRYPT);
m_authorizationData.authorizationResult = AuthorizationResult::OwnerAuthorized;
}
}
// Try to authorize user password
if (!m_authorizationData.isAuthorized())
{
QByteArray inputData = password + userData.validationSalt;
QByteArray hash = createHash_r56(inputData, password, false);
if (hash == userData.hash)
{
QByteArray fileEncryptionKeyInputData = password + userData.keySalt;
QByteArray fileEncryptionDecryptionKey = createHash_r56(fileEncryptionKeyInputData, password, false);
Q_ASSERT(fileEncryptionDecryptionKey.size() == 32);
AES_KEY key = { };
AES_set_decrypt_key(convertByteArrayToUcharPtr(fileEncryptionDecryptionKey), fileEncryptionDecryptionKey.size() * 8, &key);
unsigned char aesInitializationVector[AES_BLOCK_SIZE] = { };
m_authorizationData.fileEncryptionKey.resize(m_UE.size());
AES_cbc_encrypt(convertByteArrayToUcharPtr(m_UE), convertByteArrayToUcharPtr(m_authorizationData.fileEncryptionKey), m_UE.size(), &key, aesInitializationVector, AES_DECRYPT);
// We have authorized owner access
m_authorizationData.authorizationResult = AuthorizationResult::UserAuthorized;
}
}
// Stop, if we authorized the document usage
if (m_authorizationData.isAuthorized())
{
// According the PDF specification, we must also check, if flags are not manipulated.
Q_ASSERT(m_Perms.size() == AES_BLOCK_SIZE);
AES_KEY key = { };
AES_set_decrypt_key(convertByteArrayToUcharPtr(m_authorizationData.fileEncryptionKey), m_authorizationData.fileEncryptionKey.size() * 8, &key);
QByteArray decodedPerms(m_Perms.size(), char(0));
AES_ecb_encrypt(convertByteArrayToUcharPtr(m_Perms), convertByteArrayToUcharPtr(decodedPerms), &key, AES_DECRYPT);
// 1) Checks, if bytes 9, 10, 11 are 'a', 'd', 'b'
if (decodedPerms[9] != 'a' || decodedPerms[10] != 'd' || decodedPerms[11] != 'b')
{
throw PDFException(PDFTranslationContext::tr("Permissions entry in the Encryption dictionary is invalid."));
}
// 2) Verify, that bytes 0-3 are valid permissions entry
const uint32_t permissions = qFromLittleEndian(*reinterpret_cast<const uint32_t*>(decodedPerms.data()));
if (permissions != m_permissions)
{
throw PDFException(PDFTranslationContext::tr("Security permissions are manipulated. Can't open the document."));
}
// 3) Verify, that byte 8 is 'T' or 'F' and is equal to EncryptMetadata entry
if (decodedPerms[8] != 'T' && decodedPerms[8] != 'F')
{
throw PDFException(PDFTranslationContext::tr("Security permissions are manipulated. Can't open the document."));
}
if ((decodedPerms[8] == 'T') != m_encryptMetadata)
{
throw PDFException(PDFTranslationContext::tr("Security permissions are manipulated. Can't open the document."));
}
return m_authorizationData.authorizationResult;
}
break;
}
default:
return AuthorizationResult::Failed;
}
password = adjustPassword(getPasswordCallback(&passwordObtained));
}
return AuthorizationResult::Cancelled;
}
QByteArray PDFStandardSecurityHandler::decryptUsingFilter(const QByteArray& data, CryptFilter filter, PDFObjectReference reference) const
{
QByteArray decryptedData;
Q_ASSERT(m_authorizationData.isAuthorized());
struct AES_data
{
QByteArray initializationVector;
QByteArray paddedData;
};
auto prepareAES_data = [](const QByteArray& data)
{
AES_data result;
result.initializationVector = data.left(AES_BLOCK_SIZE);
// This is an error. But to handle it, we resize the vector
// with arbitrary data.
if (result.initializationVector.size() < AES_BLOCK_SIZE)
{
result.initializationVector.resize(AES_BLOCK_SIZE);
}
result.paddedData = data.mid(AES_BLOCK_SIZE);
// Add padding remainder according to the specification
int size = result.paddedData.size();
int paddingRemainder = AES_BLOCK_SIZE - (size % AES_BLOCK_SIZE);
for (int i = 0; i < paddingRemainder; ++i)
{
result.paddedData.push_back(paddingRemainder);
}
return result;
};
switch (filter.type)
{
case CryptFilterType::None: // The application shall decrypt the data using the security handler
{
// This shouldn't occur, because in case the used filter has None value, then default filter
// is used and default filter can't have this value.
Q_ASSERT(false);
break;
}
case CryptFilterType::V2: // Use file encryption key for RC4 algorithm
{
std::vector<uint8_t> inputKeyData = convertByteArrayToVector(m_authorizationData.fileEncryptionKey);
uint32_t objectNumber = qToLittleEndian(static_cast<uint32_t>(reference.objectNumber));
uint32_t generation = qToLittleEndian(static_cast<uint32_t>(reference.generation));
inputKeyData.insert(inputKeyData.cend(), { uint8_t(objectNumber & 0xFF), uint8_t((objectNumber >> 8) & 0xFF), uint8_t((objectNumber >> 16) & 0xFF), uint8_t(generation & 0xFF), uint8_t((generation >> 8) & 0xFF) });
std::vector<uint8_t> objectEncryptionKey(MD5_DIGEST_LENGTH, uint8_t(0));
MD5(inputKeyData.data(), inputKeyData.size(), objectEncryptionKey.data());
// Use up to (n + 5) bytes, maximally 16, from the digest as object encryption key
size_t objectEncryptionKeySize = qMin(filter.keyLength + 5, MD5_DIGEST_LENGTH);
objectEncryptionKey.resize(objectEncryptionKeySize);
decryptedData.resize(data.size());
RC4_KEY key = { };
RC4_set_key(&key, static_cast<int>(objectEncryptionKey.size()), objectEncryptionKey.data());
RC4(&key, data.size(), convertByteArrayToUcharPtr(data), convertByteArrayToUcharPtr(decryptedData));
break;
}
case CryptFilterType::AESV2: // Use file encryption key for AES algorithm
{
std::vector<uint8_t> inputKeyData = convertByteArrayToVector(m_authorizationData.fileEncryptionKey);
uint32_t objectNumber = qToLittleEndian(static_cast<uint32_t>(reference.objectNumber));
uint32_t generation = qToLittleEndian(static_cast<uint32_t>(reference.generation));
inputKeyData.insert(inputKeyData.cend(), { uint8_t(objectNumber & 0xFF), uint8_t((objectNumber >> 8) & 0xFF), uint8_t((objectNumber >> 16) & 0xFF), uint8_t(generation & 0xFF), uint8_t((generation >> 8) & 0xFF), 0x73, 0x41, 0x6C, 0x54 });
std::vector<uint8_t> objectEncryptionKey(MD5_DIGEST_LENGTH, uint8_t(0));
MD5(inputKeyData.data(), inputKeyData.size(), objectEncryptionKey.data());
// For AES algorithm, always use 16 bytes key (128 bit encryption mode)
AES_KEY key = { };
AES_set_decrypt_key(objectEncryptionKey.data(), static_cast<int>(objectEncryptionKey.size()) * 8, &key);
AES_data aes_data = prepareAES_data(data);
if (!aes_data.paddedData.isEmpty())
{
decryptedData.resize(aes_data.paddedData.size());
AES_cbc_encrypt(convertByteArrayToUcharPtr(aes_data.paddedData), convertByteArrayToUcharPtr(decryptedData), aes_data.paddedData.length(), &key, convertByteArrayToUcharPtr(aes_data.initializationVector), AES_DECRYPT);
decryptedData = decryptedData.left(data.length() - AES_BLOCK_SIZE);
}
break;
}
case CryptFilterType::AESV3: // Use file encryption key for AES 256 bit algorithm
{
Q_ASSERT(m_authorizationData.fileEncryptionKey.size() == 32);
AES_KEY key = { };
AES_set_decrypt_key(convertByteArrayToUcharPtr(m_authorizationData.fileEncryptionKey), static_cast<int>(m_authorizationData.fileEncryptionKey.size()) * 8, &key);
AES_data aes_data = prepareAES_data(data);
if (!aes_data.paddedData.isEmpty())
{
decryptedData.resize(aes_data.paddedData.size());
AES_cbc_encrypt(convertByteArrayToUcharPtr(aes_data.paddedData), convertByteArrayToUcharPtr(decryptedData), aes_data.paddedData.length(), &key, convertByteArrayToUcharPtr(aes_data.initializationVector), AES_DECRYPT);
decryptedData = decryptedData.left(data.length() - AES_BLOCK_SIZE);
}
break;
}
case CryptFilterType::Identity: // Don't decrypt anything, use identity function
{
decryptedData = data;
break;
}
}
return decryptedData;
}
QByteArray PDFStandardSecurityHandler::decrypt(const QByteArray& data, PDFObjectReference reference, PDFSecurityHandler::EncryptionScope encryptionScope) const
{
CryptFilter filter = m_filterDefault;
switch (encryptionScope)
{
case EncryptionScope::String:
{
if (m_filterStrings.type != CryptFilterType::None)
{
filter = m_filterStrings;
}
break;
}
case EncryptionScope::Stream:
{
if (m_filterStreams.type != CryptFilterType::None)
{
filter = m_filterStreams;
}
break;
}
case EncryptionScope::EmbeddedFile:
{
if (m_filterEmbeddedFiles.type != CryptFilterType::None)
{
filter = m_filterEmbeddedFiles;
}
break;
}
}
return decryptUsingFilter(data, filter, reference);
}
QByteArray PDFStandardSecurityHandler::decryptByFilter(const QByteArray& data, const QByteArray& filterName, PDFObjectReference reference) const
{
auto it = m_cryptFilters.find(filterName);
if (it == m_cryptFilters.cend())
{
throw PDFException(PDFTranslationContext::tr("Crypt filter '%1' not found.").arg(QString::fromLatin1(filterName)));
}
return decryptUsingFilter(data, it->second, reference);
}
QByteArray PDFStandardSecurityHandler::createFileEncryptionKey(const QByteArray& password) const
{
QByteArray result;
switch (m_R)
{
case 2:
case 3:
case 4:
{
std::array<uint8_t, 32> paddedPassword = createPaddedPassword32(password);
uint32_t transformedPermissions = qToLittleEndian(m_permissions);
MD5_CTX context = { };
MD5_Init(&context);
MD5_Update(&context, paddedPassword.data(), paddedPassword.size());
MD5_Update(&context, m_O.constData(), m_O.size());
MD5_Update(&context, &transformedPermissions, sizeof(transformedPermissions));
MD5_Update(&context, m_ID.constData(), m_ID.size());
if (!m_encryptMetadata)
{
constexpr uint32_t value = 0xFFFFFFFF;
MD5_Update(&context, &value, sizeof(value));
}
std::array<uint8_t, MD5_DIGEST_LENGTH> fileEncryptionKey;
MD5_Final(fileEncryptionKey.data(), &context);
const int keyByteLength = m_keyLength / 8;
if (keyByteLength > MD5_DIGEST_LENGTH)
{
throw PDFException(PDFTranslationContext::tr("Encryption key length (%1) exceeded maximal value of.").arg(keyByteLength).arg(MD5_DIGEST_LENGTH));
}
if (m_R >= 3)
{
for (int i = 0; i < 50; ++i)
{
MD5_Init(&context);
MD5_Update(&context, fileEncryptionKey.data(), keyByteLength);
MD5_Final(fileEncryptionKey.data(), &context);
}
}
result.resize(keyByteLength);
std::copy_n(fileEncryptionKey.cbegin(), keyByteLength, result.begin());
break;
}
case 5:
case 6:
{
// This function must not be called with revision 5/6
Q_ASSERT(false);
break;
}
default:
{
throw PDFException(PDFTranslationContext::tr("Revision %1 of standard security handler is not supported.").arg(m_R));
}
}
return result;
}
QByteArray PDFStandardSecurityHandler::createEntryValueU_r234(const QByteArray& fileEncryptionKey) const
{
QByteArray result;
switch (m_R)
{
case 2:
{
RC4_KEY key = { };
RC4_set_key(&key, fileEncryptionKey.size(), convertByteArrayToUcharPtr(fileEncryptionKey));
result.resize(static_cast<int>(PDFPasswordPadding.size()));
RC4(&key, PDFPasswordPadding.size(), PDFPasswordPadding.data(), convertByteArrayToUcharPtr(result));
break;
}
case 3:
case 4:
{
std::array<uint8_t, MD5_DIGEST_LENGTH> hash;
MD5_CTX context = { };
MD5_Init(&context);
MD5_Update(&context, PDFPasswordPadding.data(), PDFPasswordPadding.size());
MD5_Update(&context, m_ID.data(), m_ID.size());
MD5_Final(hash.data(), &context);
RC4_KEY key = { };
RC4_set_key(&key, fileEncryptionKey.size(), convertByteArrayToUcharPtr(fileEncryptionKey));
std::array<uint8_t, MD5_DIGEST_LENGTH> encryptedHash;
RC4(&key, hash.size(), hash.data(), encryptedHash.data());
QByteArray transformedKey = fileEncryptionKey;
for (int i = 1; i <= 19; ++i)
{
for (int j = 0, keySize = fileEncryptionKey.size(); j < keySize; ++j)
{
transformedKey[j] = static_cast<uint8_t>(fileEncryptionKey[j]) ^ static_cast<uint8_t>(i);
}
RC4_set_key(&key, transformedKey.size(), convertByteArrayToUcharPtr(transformedKey));
RC4(&key, encryptedHash.size(), encryptedHash.data(), encryptedHash.data());
}
// We do a hack here. In the PDF's specification, it is written, that arbitrary 16 bytes
// are appended to the 16 bytes result. We use the last 16 bytes of the U entry, because we
// want to compare byte arrays entirely (otherwise we must compare only 16 bytes to authenticate
// user password).
result = m_U;
std::copy_n(encryptedHash.begin(), encryptedHash.size(), result.begin());
break;
}
default:
{
throw PDFException(PDFTranslationContext::tr("Revision %1 of standard security handler is not supported.").arg(m_R));
}
}
return result;
}
QByteArray PDFStandardSecurityHandler::createUserPasswordFromOwnerPassword(const QByteArray& password) const
{
QByteArray result;
std::array<uint8_t, 32> paddedPassword = createPaddedPassword32(password);
std::array<uint8_t, MD5_DIGEST_LENGTH> hash;
MD5_CTX context = { };
MD5_Init(&context);
MD5_Update(&context, paddedPassword.data(), paddedPassword.size());
MD5_Final(hash.data(), &context);
const int keyByteLength = m_keyLength / 8;
if (keyByteLength > MD5_DIGEST_LENGTH)
{
throw PDFException(PDFTranslationContext::tr("Encryption key length (%1) exceeded maximal value of.").arg(keyByteLength).arg(MD5_DIGEST_LENGTH));
}
if (m_R >= 3)
{
for (int i = 0; i < 50; ++i)
{
MD5_Init(&context);
MD5_Update(&context, hash.data(), keyByteLength);
MD5_Final(hash.data(), &context);
}
}
switch (m_R)
{
case 2:
{
RC4_KEY key = { };
RC4_set_key(&key, keyByteLength, hash.data());
result.resize(m_O.size());
RC4(&key, m_O.size(), convertByteArrayToUcharPtr(m_O), convertByteArrayToUcharPtr(result));
break;
}
case 3:
case 4:
{
QByteArray buffer = m_O;
QByteArray transformedKey;
transformedKey.resize(keyByteLength);
std::copy_n(hash.data(), keyByteLength, transformedKey.data());
for (int i = 19; i >= 0; --i)
{
for (int j = 0, keySize = transformedKey.size(); j < keySize; ++j)
{
transformedKey[j] = static_cast<uint8_t>(hash[j]) ^ static_cast<uint8_t>(i);
}
RC4_KEY key = { };
RC4_set_key(&key, transformedKey.size(), convertByteArrayToUcharPtr(transformedKey));
RC4(&key, buffer.size(), convertByteArrayToUcharPtr(buffer), convertByteArrayToUcharPtr(buffer));
}
result = buffer;
break;
}
default:
{
throw PDFException(PDFTranslationContext::tr("Revision %1 of standard security handler is not supported.").arg(m_R));
}
}
return result;
}
std::array<uint8_t, 32> PDFStandardSecurityHandler::createPaddedPassword32(const QByteArray& password) const
{
std::array<uint8_t, 32> result = { };
int copiedBytes = qMin<int>(static_cast<int>(result.size()), password.size());
auto it = result.begin();
for (int i = 0; i < copiedBytes; ++i)
{
*it++ = static_cast<uint8_t>(password[i]);
}
auto itPadding = PDFPasswordPadding.cbegin();
for (; it != result.cend();)
{
Q_ASSERT(itPadding != PDFPasswordPadding.cend());
*it++ = *itPadding++;
}
return result;
}
QByteArray PDFStandardSecurityHandler::createHash_r6(const QByteArray& input, const QByteArray& inputPassword, bool useUserKey) const
{
QByteArray result;
// First compute sha-256 digest of the input
std::array<uint8_t, SHA256_DIGEST_LENGTH> inputDigest = { };
SHA256(convertByteArrayToUcharPtr(input), input.size(), inputDigest.data());
std::vector<uint8_t> K(inputDigest.cbegin(), inputDigest.cend());
// Fill the user key, if we use it
std::vector<uint8_t> userKey;
if (useUserKey)
{
userKey.resize(m_U.size());
std::copy_n(m_U.constData(), m_U.size(), userKey.begin());
}
const size_t userKeySize = userKey.size();
// Fill the input password
std::vector<uint8_t> password(inputPassword.constData(), inputPassword.constData() + inputPassword.size());
const size_t passwordSize = password.size();
std::vector<uint8_t> K1;
std::vector<uint8_t> E;
int round = 0;
while (round < 64 || round < E.back() + 32)
{
const size_t blockCount = 64;
const size_t KSize = K.size();
const size_t sequenceSize = passwordSize + KSize + userKeySize;
const size_t totalSize = blockCount * sequenceSize;
// Resize the arrays
K1.resize(totalSize);
E.resize(totalSize);
// a) fill the input array K1 with data
auto it = K1.begin();
for (size_t i = 0; i < blockCount; ++i)
{
std::copy_n(password.cbegin(), passwordSize, it);
std::advance(it, passwordSize);
std::copy_n(K.cbegin(), KSize, it);
std::advance(it, KSize);
std::copy_n(userKey.cbegin(), userKeySize, it);
std::advance(it, userKeySize);
}
Q_ASSERT(it == K1.cend());
Q_ASSERT(K.size() >= 32);
// b) encrypt K1 with AES-128 in CBC mode, first 16 bytes of K is key,
// second 16 bytes in K is initialization vector for AES algorithm.
AES_KEY key = { };
AES_set_encrypt_key(K.data(), 128, &key);
AES_cbc_encrypt(K1.data(), E.data(), K1.size(), &key, K.data() + 16, AES_ENCRYPT);
// c) we take first 16 bytes from E as unsigned 128 bit big-endian integer and compute
// remainder modulo 3. Then we decide which SHA function we will use.
// We can't directly modulo 128 bit unsigned number, because we do not have 128 bit arithmetic (yet).
// We will use following trick from https://math.stackexchange.com/questions/2727954/bit-representation-and-divisibility-by-3
//
// 2^n mod 3 = 2 for n = 1, 3, 5, 7, 9, ...
// 2^n mod 3 = 1 for n = 0, 2, 4, 6, 8, ...
//
// Also, it doesn't matter the endianity of the numbers, becase for example, when we change endianity of 16 bit
// numbers, then bits 0-7 became 8-15, so even/odd bits become also even/odd.
int remainderAccumulator = 0;
for (size_t i = 0; i < 16; ++i)
{
uint8_t byte = E[i];
int currentRemainder = 1;
for (uint8_t i = 0; i < 8; ++i)
{
if ((byte >> i) & 1)
{
remainderAccumulator += currentRemainder;
}
// We alternate the remainder 1, 2, 1, 2, 1, 2, ...
currentRemainder = 3 - currentRemainder;
}
}
remainderAccumulator = remainderAccumulator % 3;
// d) according to the remainder, decide, which function we will use
switch (remainderAccumulator)
{
case 0:
{
K.resize(SHA256_DIGEST_LENGTH);
SHA256(E.data(), E.size(), K.data());
break;
}
case 1:
{
K.resize(SHA384_DIGEST_LENGTH);
SHA384(E.data(), E.size(), K.data());
break;
}
case 2:
{
K.resize(SHA512_DIGEST_LENGTH);
SHA512(E.data(), E.size(), K.data());
break;
}
default:
{
// Invalid value, can't occur
Q_ASSERT(false);
break;
}
}
++round;
}
Q_ASSERT(K.size() >= 32);
// Clamp result to 32 bytes
result.resize(32);
std::copy_n(K.data(), 32, result.data());
return result;
}
PDFStandardSecurityHandler::UserOwnerData_r6 PDFStandardSecurityHandler::parseParts(const QByteArray& data) const
{
UserOwnerData_r6 result;
Q_ASSERT(data.size() == 48);
result.hash = data.left(32);
result.validationSalt = data.mid(32, 8);
result.keySalt = data.mid(40, 8);
return result;
}
QByteArray PDFStandardSecurityHandler::adjustPassword(const QString& password)
{
QByteArray result;
switch (m_R)
{
case 2:
case 3:
case 4:
{
// According to the PDF specification, convert string to PDFDocEncoding encoding
result = PDFEncoding::convertToEncoding(password, PDFEncoding::Encoding::PDFDoc);
break;
}
case 5:
case 6:
{
// According to the PDF specification, use SASLprep profile for stringprep RFC 4013, please see these websites:
// - RFC 4013: https://tools.ietf.org/html/rfc4013 (SASLprep profile for stringprep algorithm)
// - RFC 3454: https://tools.ietf.org/html/rfc3454 (stringprep algorithm - preparation of internationalized strings)
//
// Note: we don't do checks according the RFC 4013, just use the mapping and normalize string in KC
QString preparedPassword;
preparedPassword.reserve(password.size());
// RFC 4013 Section 2.1, use mapping
for (const QChar character : password)
{
if (isUnicodeMappedToNothing(character.unicode()))
{
// Mapped to nothing
continue;
}
if (isUnicodeNonAsciiSpaceCharacter(character.unicode()))
{
// Map to space character
preparedPassword += QChar(QChar::Space);
}
else
{
preparedPassword += character;
}
}
// RFC 4013, Section 2.2, normalization to KC
preparedPassword = preparedPassword.normalized(QString::NormalizationForm_KC);
// We don't do other checks. We will transform password to the UTF-8 encoding
// and according the PDF specification, we take only first 127 characters.
result = preparedPassword.toUtf8().left(127);
}
default:
break;
}
return result;
}
bool PDFStandardSecurityHandler::isUnicodeNonAsciiSpaceCharacter(ushort unicode)
{
switch (unicode)
{
case 0x00A0:
case 0x1680:
case 0x2000:
case 0x2001:
case 0x2002:
case 0x2003:
case 0x2004:
case 0x2005:
case 0x2006:
case 0x2007:
case 0x2008:
case 0x2009:
case 0x200A:
case 0x200B:
case 0x202F:
case 0x205F:
case 0x3000:
return true;
default:
return false;
}
}
bool PDFStandardSecurityHandler::isUnicodeMappedToNothing(ushort unicode)
{
switch (unicode)
{
case 0x00AD:
case 0x034F:
case 0x1806:
case 0x180B:
case 0x180C:
case 0x180D:
case 0x200B:
case 0x200C:
case 0x200D:
return true;
default:
return false;
}
}
} // namespace pdf
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