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qpdf/libqpdf/QPDF_encryption.cc

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// This file implements methods from the QPDF class that involve
// encryption.
#include <qpdf/assert_debug.h>
#include <qpdf/QPDF.hh>
#include <qpdf/QPDFExc.hh>
#include <qpdf/MD5.hh>
#include <qpdf/Pl_AES_PDF.hh>
#include <qpdf/Pl_Buffer.hh>
#include <qpdf/Pl_RC4.hh>
#include <qpdf/Pl_SHA2.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <qpdf/RC4.hh>
#include <algorithm>
#include <cstring>
static unsigned char const padding_string[] = {
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};
static unsigned int const key_bytes = 32;
// V4 key lengths apply to V <= 4
static unsigned int const OU_key_bytes_V4 = sizeof(MD5::Digest);
static unsigned int const OU_key_bytes_V5 = 48;
static unsigned int const OUE_key_bytes_V5 = 32;
static unsigned int const Perms_key_bytes_V5 = 16;
int
QPDF::EncryptionData::getV() const
{
return this->V;
}
int
QPDF::EncryptionData::getR() const
{
return this->R;
}
int
QPDF::EncryptionData::getLengthBytes() const
{
return this->Length_bytes;
}
int
QPDF::EncryptionData::getP() const
{
return this->P;
}
std::string const&
QPDF::EncryptionData::getO() const
{
return this->O;
}
std::string const&
QPDF::EncryptionData::getU() const
{
return this->U;
}
std::string const&
QPDF::EncryptionData::getOE() const
{
return this->OE;
}
std::string const&
QPDF::EncryptionData::getUE() const
{
return this->UE;
}
std::string const&
QPDF::EncryptionData::getPerms() const
{
return this->Perms;
}
std::string const&
QPDF::EncryptionData::getId1() const
{
return this->id1;
}
bool
QPDF::EncryptionData::getEncryptMetadata() const
{
return this->encrypt_metadata;
}
void
QPDF::EncryptionData::setO(std::string const& O)
{
this->O = O;
}
void
QPDF::EncryptionData::setU(std::string const& U)
{
this->U = U;
}
void
QPDF::EncryptionData::setV5EncryptionParameters(
std::string const& O,
std::string const& OE,
std::string const& U,
std::string const& UE,
std::string const& Perms)
{
this->O = O;
this->OE = OE;
this->U = U;
this->UE = UE;
this->Perms = Perms;
}
static void
pad_or_truncate_password_V4(std::string const& password, char k1[key_bytes])
{
size_t password_bytes = std::min(QIntC::to_size(key_bytes), password.length());
size_t pad_bytes = key_bytes - password_bytes;
memcpy(k1, password.c_str(), password_bytes);
memcpy(k1 + password_bytes, padding_string, pad_bytes);
}
void
QPDF::trim_user_password(std::string& user_password)
{
// Although unnecessary, this routine trims the padding string from the end of a user password.
// Its only purpose is for recovery of user passwords which is done in the test suite.
char const* cstr = user_password.c_str();
size_t len = user_password.length();
if (len < key_bytes) {
return;
}
char const* p1 = cstr;
char const* p2 = nullptr;
while ((p2 = strchr(p1, '\x28')) != nullptr) {
size_t idx = toS(p2 - cstr);
if (memcmp(p2, padding_string, len - idx) == 0) {
user_password = user_password.substr(0, idx);
return;
} else {
QTC::TC("qpdf", "QPDF_encryption skip 0x28");
p1 = p2 + 1;
}
}
}
static std::string
pad_or_truncate_password_V4(std::string const& password)
{
char k1[key_bytes];
pad_or_truncate_password_V4(password, k1);
return {k1, key_bytes};
}
static std::string
truncate_password_V5(std::string const& password)
{
return password.substr(0, std::min(static_cast<size_t>(127), password.length()));
}
static void
iterate_md5_digest(MD5& md5, MD5::Digest& digest, int iterations, int key_len)
{
md5.digest(digest);
for (int i = 0; i < iterations; ++i) {
MD5 m;
m.encodeDataIncrementally(reinterpret_cast<char*>(digest), QIntC::to_size(key_len));
m.digest(digest);
}
}
static void
iterate_rc4(
unsigned char* data,
size_t data_len,
unsigned char* okey,
int key_len,
int iterations,
bool reverse)
{
auto key_ph = std::make_unique<unsigned char[]>(QIntC::to_size(key_len));
unsigned char* key = key_ph.get();
for (int i = 0; i < iterations; ++i) {
int const xor_value = (reverse ? iterations - 1 - i : i);
for (int j = 0; j < key_len; ++j) {
key[j] = static_cast<unsigned char>(okey[j] ^ xor_value);
}
RC4 rc4(key, QIntC::to_int(key_len));
rc4.process(data, data_len, data);
}
}
static std::string
process_with_aes(
std::string const& key,
bool encrypt,
std::string const& data,
size_t outlength = 0,
unsigned int repetitions = 1,
unsigned char const* iv = nullptr,
size_t iv_length = 0)
{
Pl_Buffer buffer("buffer");
Pl_AES_PDF aes(
"aes", &buffer, encrypt, QUtil::unsigned_char_pointer(key), QIntC::to_uint(key.length()));
if (iv) {
aes.setIV(iv, iv_length);
} else {
aes.useZeroIV();
}
aes.disablePadding();
for (unsigned int i = 0; i < repetitions; ++i) {
aes.writeString(data);
}
aes.finish();
if (outlength == 0) {
return buffer.getString();
} else {
return buffer.getString().substr(0, outlength);
}
}
static std::string
hash_V5(
std::string const& password,
std::string const& salt,
std::string const& udata,
QPDF::EncryptionData const& data)
{
Pl_SHA2 hash(256);
hash.writeString(password);
hash.writeString(salt);
hash.writeString(udata);
hash.finish();
std::string K = hash.getRawDigest();
std::string result;
if (data.getR() < 6) {
result = K;
} else {
// Algorithm 2.B from ISO 32000-1 chapter 7: Computing a hash
int round_number = 0;
bool done = false;
while (!done) {
// The hash algorithm has us setting K initially to the R5 value and then repeating a
// series of steps 64 times before starting with the termination case testing. The
// wording of the specification is very unclear as to the exact number of times it
// should be run since the wording about whether the initial setup counts as round 0 or
// not is ambiguous. This code counts the initial setup (R5) value as round 0, which
// appears to be correct. This was determined to be correct by increasing or decreasing
// the number of rounds by 1 or 2 from this value and generating 20 test files. In this
// interpretation, all the test files worked with Adobe Reader X. In the other
// configurations, many of the files did not work, and we were accurately able to
// predict which files didn't work by looking at the conditions under which we
// terminated repetition.
++round_number;
std::string K1 = password + K + udata;
qpdf_assert_debug(K.length() >= 32);
std::string E = process_with_aes(
K.substr(0, 16),
true,
K1,
0,
64,
QUtil::unsigned_char_pointer(K.substr(16, 16)),
16);
// E_mod_3 is supposed to be mod 3 of the first 16 bytes of E taken as as a (128-bit)
// big-endian number. Since (xy mod n) is equal to ((x mod n) + (y mod n)) mod n and
// since 256 mod n is 1, we can just take the sums of the the mod 3s of each byte to get
// the same result.
int E_mod_3 = 0;
for (unsigned int i = 0; i < 16; ++i) {
E_mod_3 += static_cast<unsigned char>(E.at(i));
}
E_mod_3 %= 3;
int next_hash = ((E_mod_3 == 0) ? 256 : (E_mod_3 == 1) ? 384 : 512);
Pl_SHA2 sha2(next_hash);
sha2.writeString(E);
sha2.finish();
K = sha2.getRawDigest();
if (round_number >= 64) {
unsigned int ch = static_cast<unsigned char>(*(E.rbegin()));
if (ch <= QIntC::to_uint(round_number - 32)) {
done = true;
}
}
}
result = K.substr(0, 32);
}
return result;
}
static void
pad_short_parameter(std::string& param, size_t max_len)
{
if (param.length() < max_len) {
QTC::TC("qpdf", "QPDF_encryption pad short parameter");
param.append(max_len - param.length(), '\0');
}
}
std::string
QPDF::compute_data_key(
std::string const& encryption_key,
int objid,
int generation,
bool use_aes,
int encryption_V,
int encryption_R)
{
// Algorithm 3.1 from the PDF 1.7 Reference Manual
std::string result = encryption_key;
if (encryption_V >= 5) {
// Algorithm 3.1a (PDF 1.7 extension level 3): just use encryption key straight.
return result;
}
// Append low three bytes of object ID and low two bytes of generation
result.append(1, static_cast<char>(objid & 0xff));
result.append(1, static_cast<char>((objid >> 8) & 0xff));
result.append(1, static_cast<char>((objid >> 16) & 0xff));
result.append(1, static_cast<char>(generation & 0xff));
result.append(1, static_cast<char>((generation >> 8) & 0xff));
if (use_aes) {
result += "sAlT";
}
MD5 md5;
md5.encodeDataIncrementally(result.c_str(), result.length());
MD5::Digest digest;
md5.digest(digest);
return {reinterpret_cast<char*>(digest), std::min(result.length(), toS(16))};
}
std::string
QPDF::compute_encryption_key(std::string const& password, EncryptionData const& data)
{
if (data.getV() >= 5) {
// For V >= 5, the encryption key is generated and stored in the file, encrypted separately
// with both user and owner passwords.
return recover_encryption_key_with_password(password, data);
} else {
// For V < 5, the encryption key is derived from the user
// password.
return compute_encryption_key_from_password(password, data);
}
}
std::string
QPDF::compute_encryption_key_from_password(std::string const& password, EncryptionData const& data)
{
// Algorithm 3.2 from the PDF 1.7 Reference Manual
// This code does not properly handle Unicode passwords. Passwords are supposed to be converted
// from OS codepage characters to PDFDocEncoding. Unicode passwords are supposed to be
// converted to OS codepage before converting to PDFDocEncoding. We instead require the
// password to be presented in its final form.
MD5 md5;
md5.encodeDataIncrementally(pad_or_truncate_password_V4(password).c_str(), key_bytes);
md5.encodeDataIncrementally(data.getO().c_str(), key_bytes);
char pbytes[4];
int P = data.getP();
pbytes[0] = static_cast<char>(P & 0xff);
pbytes[1] = static_cast<char>((P >> 8) & 0xff);
pbytes[2] = static_cast<char>((P >> 16) & 0xff);
pbytes[3] = static_cast<char>((P >> 24) & 0xff);
md5.encodeDataIncrementally(pbytes, 4);
md5.encodeDataIncrementally(data.getId1().c_str(), data.getId1().length());
if ((data.getR() >= 4) && (!data.getEncryptMetadata())) {
char bytes[4];
memset(bytes, 0xff, 4);
md5.encodeDataIncrementally(bytes, 4);
}
MD5::Digest digest;
int key_len = std::min(toI(sizeof(digest)), data.getLengthBytes());
iterate_md5_digest(md5, digest, ((data.getR() >= 3) ? 50 : 0), key_len);
return {reinterpret_cast<char*>(digest), toS(key_len)};
}
static void
compute_O_rc4_key(
std::string const& user_password,
std::string const& owner_password,
QPDF::EncryptionData const& data,
unsigned char key[OU_key_bytes_V4])
{
if (data.getV() >= 5) {
throw std::logic_error("compute_O_rc4_key called for file with V >= 5");
}
std::string password = owner_password;
if (password.empty()) {
password = user_password;
}
MD5 md5;
md5.encodeDataIncrementally(pad_or_truncate_password_V4(password).c_str(), key_bytes);
MD5::Digest digest;
int key_len = std::min(QIntC::to_int(sizeof(digest)), data.getLengthBytes());
iterate_md5_digest(md5, digest, ((data.getR() >= 3) ? 50 : 0), key_len);
memcpy(key, digest, OU_key_bytes_V4);
}
static std::string
compute_O_value(
std::string const& user_password,
std::string const& owner_password,
QPDF::EncryptionData const& data)
{
// Algorithm 3.3 from the PDF 1.7 Reference Manual
unsigned char O_key[OU_key_bytes_V4];
compute_O_rc4_key(user_password, owner_password, data, O_key);
char upass[key_bytes];
pad_or_truncate_password_V4(user_password, upass);
std::string k1(reinterpret_cast<char*>(O_key), OU_key_bytes_V4);
pad_short_parameter(k1, QIntC::to_size(data.getLengthBytes()));
iterate_rc4(
QUtil::unsigned_char_pointer(upass),
key_bytes,
O_key,
data.getLengthBytes(),
(data.getR() >= 3) ? 20 : 1,
false);
return {upass, key_bytes};
}
static std::string
compute_U_value_R2(std::string const& user_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.4 from the PDF 1.7 Reference Manual
std::string k1 = QPDF::compute_encryption_key(user_password, data);
char udata[key_bytes];
pad_or_truncate_password_V4("", udata);
pad_short_parameter(k1, QIntC::to_size(data.getLengthBytes()));
iterate_rc4(
QUtil::unsigned_char_pointer(udata),
key_bytes,
QUtil::unsigned_char_pointer(k1),
data.getLengthBytes(),
1,
false);
return {udata, key_bytes};
}
static std::string
compute_U_value_R3(std::string const& user_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.5 from the PDF 1.7 Reference Manual
std::string k1 = QPDF::compute_encryption_key(user_password, data);
MD5 md5;
md5.encodeDataIncrementally(pad_or_truncate_password_V4("").c_str(), key_bytes);
md5.encodeDataIncrementally(data.getId1().c_str(), data.getId1().length());
MD5::Digest digest;
md5.digest(digest);
pad_short_parameter(k1, QIntC::to_size(data.getLengthBytes()));
iterate_rc4(
digest,
sizeof(MD5::Digest),
QUtil::unsigned_char_pointer(k1),
data.getLengthBytes(),
20,
false);
char result[key_bytes];
memcpy(result, digest, sizeof(MD5::Digest));
// pad with arbitrary data -- make it consistent for the sake of
// testing
for (unsigned int i = sizeof(MD5::Digest); i < key_bytes; ++i) {
result[i] = static_cast<char>((i * i) % 0xff);
}
return {result, key_bytes};
}
static std::string
compute_U_value(std::string const& user_password, QPDF::EncryptionData const& data)
{
if (data.getR() >= 3) {
return compute_U_value_R3(user_password, data);
}
return compute_U_value_R2(user_password, data);
}
static bool
check_user_password_V4(std::string const& user_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.6 from the PDF 1.7 Reference Manual
std::string u_value = compute_U_value(user_password, data);
size_t to_compare = ((data.getR() >= 3) ? sizeof(MD5::Digest) : key_bytes);
return (memcmp(data.getU().c_str(), u_value.c_str(), to_compare) == 0);
}
static bool
check_user_password_V5(std::string const& user_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.11 from the PDF 1.7 extension level 3
std::string user_data = data.getU().substr(0, 32);
std::string validation_salt = data.getU().substr(32, 8);
std::string password = truncate_password_V5(user_password);
return (hash_V5(password, validation_salt, "", data) == user_data);
}
static bool
check_user_password(std::string const& user_password, QPDF::EncryptionData const& data)
{
if (data.getV() < 5) {
return check_user_password_V4(user_password, data);
} else {
return check_user_password_V5(user_password, data);
}
}
static bool
check_owner_password_V4(
std::string& user_password, std::string const& owner_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.7 from the PDF 1.7 Reference Manual
unsigned char key[OU_key_bytes_V4];
compute_O_rc4_key(user_password, owner_password, data, key);
unsigned char O_data[key_bytes];
memcpy(O_data, QUtil::unsigned_char_pointer(data.getO()), key_bytes);
std::string k1(reinterpret_cast<char*>(key), OU_key_bytes_V4);
pad_short_parameter(k1, QIntC::to_size(data.getLengthBytes()));
iterate_rc4(
O_data,
key_bytes,
QUtil::unsigned_char_pointer(k1),
data.getLengthBytes(),
(data.getR() >= 3) ? 20 : 1,
true);
std::string new_user_password = std::string(reinterpret_cast<char*>(O_data), key_bytes);
bool result = false;
if (check_user_password(new_user_password, data)) {
result = true;
user_password = new_user_password;
}
return result;
}
static bool
check_owner_password_V5(std::string const& owner_password, QPDF::EncryptionData const& data)
{
// Algorithm 3.12 from the PDF 1.7 extension level 3
std::string user_data = data.getU().substr(0, 48);
std::string owner_data = data.getO().substr(0, 32);
std::string validation_salt = data.getO().substr(32, 8);
std::string password = truncate_password_V5(owner_password);
return (hash_V5(password, validation_salt, user_data, data) == owner_data);
}
static bool
check_owner_password(
std::string& user_password, std::string const& owner_password, QPDF::EncryptionData const& data)
{
if (data.getV() < 5) {
return check_owner_password_V4(user_password, owner_password, data);
} else {
return check_owner_password_V5(owner_password, data);
}
}
std::string
QPDF::recover_encryption_key_with_password(std::string const& password, EncryptionData const& data)
{
// Disregard whether Perms is valid.
bool disregard;
return recover_encryption_key_with_password(password, data, disregard);
}
static void
compute_U_UE_value_V5(
std::string const& user_password,
std::string const& encryption_key,
QPDF::EncryptionData const& data,
std::string& U,
std::string& UE)
{
// Algorithm 3.8 from the PDF 1.7 extension level 3
char k[16];
QUtil::initializeWithRandomBytes(reinterpret_cast<unsigned char*>(k), sizeof(k));
std::string validation_salt(k, 8);
std::string key_salt(k + 8, 8);
U = hash_V5(user_password, validation_salt, "", data) + validation_salt + key_salt;
std::string intermediate_key = hash_V5(user_password, key_salt, "", data);
UE = process_with_aes(intermediate_key, true, encryption_key);
}
static void
compute_O_OE_value_V5(
std::string const& owner_password,
std::string const& encryption_key,
QPDF::EncryptionData const& data,
std::string const& U,
std::string& O,
std::string& OE)
{
// Algorithm 3.9 from the PDF 1.7 extension level 3
char k[16];
QUtil::initializeWithRandomBytes(reinterpret_cast<unsigned char*>(k), sizeof(k));
std::string validation_salt(k, 8);
std::string key_salt(k + 8, 8);
O = hash_V5(owner_password, validation_salt, U, data) + validation_salt + key_salt;
std::string intermediate_key = hash_V5(owner_password, key_salt, U, data);
OE = process_with_aes(intermediate_key, true, encryption_key);
}
void
compute_Perms_value_V5_clear(
std::string const& encryption_key, QPDF::EncryptionData const& data, unsigned char k[16])
{
// From algorithm 3.10 from the PDF 1.7 extension level 3
unsigned long long extended_perms =
0xffffffff00000000LL | static_cast<unsigned long long>(data.getP());
for (int i = 0; i < 8; ++i) {
k[i] = static_cast<unsigned char>(extended_perms & 0xff);
extended_perms >>= 8;
}
k[8] = data.getEncryptMetadata() ? 'T' : 'F';
k[9] = 'a';
k[10] = 'd';
k[11] = 'b';
QUtil::initializeWithRandomBytes(k + 12, 4);
}
static std::string
compute_Perms_value_V5(std::string const& encryption_key, QPDF::EncryptionData const& data)
{
// Algorithm 3.10 from the PDF 1.7 extension level 3
unsigned char k[16];
compute_Perms_value_V5_clear(encryption_key, data, k);
return process_with_aes(
encryption_key, true, std::string(reinterpret_cast<char*>(k), sizeof(k)));
}
std::string
QPDF::recover_encryption_key_with_password(
std::string const& password, EncryptionData const& data, bool& perms_valid)
{
// Algorithm 3.2a from the PDF 1.7 extension level 3
// This code does not handle Unicode passwords correctly. Empirical evidence suggests that most
// viewers don't. We are supposed to process the input string with the SASLprep (RFC 4013)
// profile of stringprep (RFC 3454) and then convert the result to UTF-8.
perms_valid = false;
std::string key_password = truncate_password_V5(password);
std::string key_salt;
std::string user_data;
std::string encrypted_file_key;
if (check_owner_password_V5(key_password, data)) {
key_salt = data.getO().substr(40, 8);
user_data = data.getU().substr(0, 48);
encrypted_file_key = data.getOE().substr(0, 32);
} else if (check_user_password_V5(key_password, data)) {
key_salt = data.getU().substr(40, 8);
encrypted_file_key = data.getUE().substr(0, 32);
}
std::string intermediate_key = hash_V5(key_password, key_salt, user_data, data);
std::string file_key = process_with_aes(intermediate_key, false, encrypted_file_key);
// Decrypt Perms and check against expected value
std::string perms_check = process_with_aes(file_key, false, data.getPerms(), 12);
unsigned char k[16];
compute_Perms_value_V5_clear(file_key, data, k);
perms_valid = (memcmp(perms_check.c_str(), k, 12) == 0);
return file_key;
}
QPDF::encryption_method_e
QPDF::interpretCF(std::shared_ptr<EncryptionParameters> encp, QPDFObjectHandle cf)
{
if (cf.isName()) {
std::string filter = cf.getName();
if (encp->crypt_filters.count(filter) != 0) {
return encp->crypt_filters[filter];
} else if (filter == "/Identity") {
return e_none;
} else {
return e_unknown;
}
} else {
// Default: /Identity
return e_none;
}
}
void
QPDF::initializeEncryption()
{
if (m->encp->encryption_initialized) {
return;
}
m->encp->encryption_initialized = true;
// After we initialize encryption parameters, we must use stored key information and never look
// at /Encrypt again. Otherwise, things could go wrong if someone mutates the encryption
// dictionary.
if (!m->trailer.hasKey("/Encrypt")) {
return;
}
// Go ahead and set m->encrypted here. That way, isEncrypted will return true even if there
// were errors reading the encryption dictionary.
m->encp->encrypted = true;
std::string id1;
QPDFObjectHandle id_obj = m->trailer.getKey("/ID");
if ((id_obj.isArray() && (id_obj.getArrayNItems() == 2) && id_obj.getArrayItem(0).isString())) {
id1 = id_obj.getArrayItem(0).getStringValue();
} else {
// Treating a missing ID as the empty string enables qpdf to decrypt some invalid encrypted
// files with no /ID that poppler can read but Adobe Reader can't.
warn(damagedPDF("trailer", "invalid /ID in trailer dictionary"));
}
QPDFObjectHandle encryption_dict = m->trailer.getKey("/Encrypt");
if (!encryption_dict.isDictionary()) {
throw damagedPDF("/Encrypt in trailer dictionary is not a dictionary");
}
if (!(encryption_dict.getKey("/Filter").isName() &&
(encryption_dict.getKey("/Filter").getName() == "/Standard"))) {
throw QPDFExc(
qpdf_e_unsupported,
m->file->getName(),
"encryption dictionary",
m->file->getLastOffset(),
"unsupported encryption filter");
}
if (!encryption_dict.getKey("/SubFilter").isNull()) {
warn(
qpdf_e_unsupported,
"encryption dictionary",
m->file->getLastOffset(),
"file uses encryption SubFilters, which qpdf does not support");
}
if (!(encryption_dict.getKey("/V").isInteger() && encryption_dict.getKey("/R").isInteger() &&
encryption_dict.getKey("/O").isString() && encryption_dict.getKey("/U").isString() &&
encryption_dict.getKey("/P").isInteger())) {
throw damagedPDF(
"encryption dictionary",
"some encryption dictionary parameters are missing or the wrong "
"type");
}
int V = encryption_dict.getKey("/V").getIntValueAsInt();
int R = encryption_dict.getKey("/R").getIntValueAsInt();
std::string O = encryption_dict.getKey("/O").getStringValue();
std::string U = encryption_dict.getKey("/U").getStringValue();
int P = static_cast<int>(encryption_dict.getKey("/P").getIntValue());
// If supporting new encryption R/V values, remember to update error message inside this if
// statement.
if (!(((R >= 2) && (R <= 6)) && ((V == 1) || (V == 2) || (V == 4) || (V == 5)))) {
throw QPDFExc(
qpdf_e_unsupported,
m->file->getName(),
"encryption dictionary",
m->file->getLastOffset(),
"Unsupported /R or /V in encryption dictionary; R = " + std::to_string(R) +
" (max 6), V = " + std::to_string(V) + " (max 5)");
}
m->encp->encryption_V = V;
m->encp->encryption_R = R;
// OE, UE, and Perms are only present if V >= 5.
std::string OE;
std::string UE;
std::string Perms;
if (V < 5) {
// These must be exactly the right number of bytes.
pad_short_parameter(O, key_bytes);
pad_short_parameter(U, key_bytes);
if (!((O.length() == key_bytes) && (U.length() == key_bytes))) {
throw damagedPDF(
"encryption dictionary",
"incorrect length for /O and/or /U in encryption dictionary");
}
} else {
if (!(encryption_dict.getKey("/OE").isString() &&
encryption_dict.getKey("/UE").isString() &&
encryption_dict.getKey("/Perms").isString())) {
throw damagedPDF(
"encryption dictionary",
"some V=5 encryption dictionary parameters are missing or the "
"wrong type");
}
OE = encryption_dict.getKey("/OE").getStringValue();
UE = encryption_dict.getKey("/UE").getStringValue();
Perms = encryption_dict.getKey("/Perms").getStringValue();
// These may be longer than the minimum number of bytes.
pad_short_parameter(O, OU_key_bytes_V5);
pad_short_parameter(U, OU_key_bytes_V5);
pad_short_parameter(OE, OUE_key_bytes_V5);
pad_short_parameter(UE, OUE_key_bytes_V5);
pad_short_parameter(Perms, Perms_key_bytes_V5);
}
int Length = 0;
if (V <= 1) {
Length = 40;
} else if (V == 4) {
Length = 128;
} else if (V == 5) {
Length = 256;
} else {
if (encryption_dict.getKey("/Length").isInteger()) {
Length = encryption_dict.getKey("/Length").getIntValueAsInt();
if ((Length % 8) || (Length < 40) || (Length > 128)) {
Length = 0;
}
}
}
if (Length == 0) {
// Still no Length? Just take a guess.
Length = 128;
}
m->encp->encrypt_metadata = true;
if ((V >= 4) && (encryption_dict.getKey("/EncryptMetadata").isBool())) {
m->encp->encrypt_metadata = encryption_dict.getKey("/EncryptMetadata").getBoolValue();
}
if ((V == 4) || (V == 5)) {
QPDFObjectHandle CF = encryption_dict.getKey("/CF");
for (auto const& filter: CF.getKeys()) {
QPDFObjectHandle cdict = CF.getKey(filter);
if (cdict.isDictionary()) {
encryption_method_e method = e_none;
if (cdict.getKey("/CFM").isName()) {
std::string method_name = cdict.getKey("/CFM").getName();
if (method_name == "/V2") {
QTC::TC("qpdf", "QPDF_encryption CFM V2");
method = e_rc4;
} else if (method_name == "/AESV2") {
QTC::TC("qpdf", "QPDF_encryption CFM AESV2");
method = e_aes;
} else if (method_name == "/AESV3") {
QTC::TC("qpdf", "QPDF_encryption CFM AESV3");
method = e_aesv3;
} else {
// Don't complain now -- maybe we won't need to reference this type.
method = e_unknown;
}
}
m->encp->crypt_filters[filter] = method;
}
}
QPDFObjectHandle StmF = encryption_dict.getKey("/StmF");
QPDFObjectHandle StrF = encryption_dict.getKey("/StrF");
QPDFObjectHandle EFF = encryption_dict.getKey("/EFF");
m->encp->cf_stream = interpretCF(m->encp, StmF);
m->encp->cf_string = interpretCF(m->encp, StrF);
if (EFF.isName()) {
// qpdf does not use this for anything other than informational purposes. This is
// intended to instruct conforming writers on which crypt filter should be used when new
// file attachments are added to a PDF file, but qpdf never generates encrypted files
// with non-default crypt filters. Prior to 10.2, I was under the mistaken impression
// that this was supposed to be used for decrypting attachments, but the code was wrong
// in a way that turns out not to have mattered because no writers were generating files
// the way I was imagining. Still, providing this information could be useful when
// looking at a file generated by something else, such as Acrobat when specifying that
// only attachments should be encrypted.
m->encp->cf_file = interpretCF(m->encp, EFF);
} else {
m->encp->cf_file = m->encp->cf_stream;
}
}
EncryptionData data(V, R, Length / 8, P, O, U, OE, UE, Perms, id1, m->encp->encrypt_metadata);
if (m->provided_password_is_hex_key) {
// ignore passwords in file
} else {
m->encp->owner_password_matched =
check_owner_password(m->encp->user_password, m->encp->provided_password, data);
if (m->encp->owner_password_matched && (V < 5)) {
// password supplied was owner password; user_password has been initialized for V < 5
if (getTrimmedUserPassword() == m->encp->provided_password) {
m->encp->user_password_matched = true;
QTC::TC("qpdf", "QPDF_encryption user matches owner V < 5");
}
} else {
m->encp->user_password_matched = check_user_password(m->encp->provided_password, data);
if (m->encp->user_password_matched) {
m->encp->user_password = m->encp->provided_password;
}
}
if (m->encp->user_password_matched && m->encp->owner_password_matched) {
QTC::TC("qpdf", "QPDF_encryption same password", (V < 5) ? 0 : 1);
}
if (!(m->encp->owner_password_matched || m->encp->user_password_matched)) {
throw QPDFExc(qpdf_e_password, m->file->getName(), "", 0, "invalid password");
}
}
if (m->provided_password_is_hex_key) {
m->encp->encryption_key = QUtil::hex_decode(m->encp->provided_password);
} else if (V < 5) {
// For V < 5, the user password is encrypted with the owner password, and the user password
// is always used for computing the encryption key.
m->encp->encryption_key = compute_encryption_key(m->encp->user_password, data);
} else {
// For V >= 5, either password can be used independently to compute the encryption key, and
// neither password can be used to recover the other.
bool perms_valid;
m->encp->encryption_key =
recover_encryption_key_with_password(m->encp->provided_password, data, perms_valid);
if (!perms_valid) {
warn(damagedPDF(
"encryption dictionary",
"/Perms field in encryption dictionary doesn't match expected "
"value"));
}
}
}
std::string
QPDF::getKeyForObject(
std::shared_ptr<EncryptionParameters> encp, QPDFObjGen const& og, bool use_aes)
{
if (!encp->encrypted) {
throw std::logic_error("request for encryption key in non-encrypted PDF");
}
if (og != encp->cached_key_og) {
encp->cached_object_encryption_key = compute_data_key(
encp->encryption_key,
og.getObj(),
og.getGen(),
use_aes,
encp->encryption_V,
encp->encryption_R);
encp->cached_key_og = og;
}
return encp->cached_object_encryption_key;
}
void
QPDF::decryptString(std::string& str, QPDFObjGen const& og)
{
if (!og.isIndirect()) {
return;
}
bool use_aes = false;
if (m->encp->encryption_V >= 4) {
switch (m->encp->cf_string) {
case e_none:
return;
case e_aes:
use_aes = true;
break;
case e_aesv3:
use_aes = true;
break;
case e_rc4:
break;
default:
warn(damagedPDF("unknown encryption filter for strings (check /StrF in "
"/Encrypt dictionary); strings may be decrypted improperly"));
// To avoid repeated warnings, reset cf_string. Assume we'd want to use AES if V == 4.
m->encp->cf_string = e_aes;
use_aes = true;
break;
}
}
std::string key = getKeyForObject(m->encp, og, use_aes);
try {
if (use_aes) {
QTC::TC("qpdf", "QPDF_encryption aes decode string");
Pl_Buffer bufpl("decrypted string");
Pl_AES_PDF pl(
"aes decrypt string",
&bufpl,
false,
QUtil::unsigned_char_pointer(key),
key.length());
pl.writeString(str);
pl.finish();
str = bufpl.getString();
} else {
QTC::TC("qpdf", "QPDF_encryption rc4 decode string");
size_t vlen = str.length();
// Using std::shared_ptr guarantees that tmp will be freed even if rc4.process throws an
// exception.
auto tmp = QUtil::make_unique_cstr(str);
RC4 rc4(QUtil::unsigned_char_pointer(key), toI(key.length()));
auto data = QUtil::unsigned_char_pointer(tmp.get());
rc4.process(data, vlen, data);
str = std::string(tmp.get(), vlen);
}
} catch (QPDFExc&) {
throw;
} catch (std::runtime_error& e) {
throw damagedPDF("error decrypting string for object " + og.unparse() + ": " + e.what());
}
}
// Prepend a decryption pipeline to 'pipeline'. The decryption pipeline (returned as
// 'decrypt_pipeline' must be owned by the caller to ensure that it stays alive while the pipeline
// is in use.
void
QPDF::decryptStream(
std::shared_ptr<EncryptionParameters> encp,
std::shared_ptr<InputSource> file,
QPDF& qpdf_for_warning,
Pipeline*& pipeline,
QPDFObjGen const& og,
QPDFObjectHandle& stream_dict,
std::unique_ptr<Pipeline>& decrypt_pipeline)
{
std::string type;
if (stream_dict.getKey("/Type").isName()) {
type = stream_dict.getKey("/Type").getName();
}
if (type == "/XRef") {
QTC::TC("qpdf", "QPDF_encryption xref stream from encrypted file");
return;
}
bool use_aes = false;
if (encp->encryption_V >= 4) {
encryption_method_e method = e_unknown;
std::string method_source = "/StmF from /Encrypt dictionary";
if (stream_dict.getKey("/Filter").isOrHasName("/Crypt")) {
if (stream_dict.getKey("/DecodeParms").isDictionary()) {
QPDFObjectHandle decode_parms = stream_dict.getKey("/DecodeParms");
if (decode_parms.isDictionaryOfType("/CryptFilterDecodeParms")) {
QTC::TC("qpdf", "QPDF_encryption stream crypt filter");
method = interpretCF(encp, decode_parms.getKey("/Name"));
method_source = "stream's Crypt decode parameters";
}
} else if (
stream_dict.getKey("/DecodeParms").isArray() &&
stream_dict.getKey("/Filter").isArray()) {
QPDFObjectHandle filter = stream_dict.getKey("/Filter");
QPDFObjectHandle decode = stream_dict.getKey("/DecodeParms");
if (filter.getArrayNItems() == decode.getArrayNItems()) {
for (int i = 0; i < filter.getArrayNItems(); ++i) {
if (filter.getArrayItem(i).isNameAndEquals("/Crypt")) {
QPDFObjectHandle crypt_params = decode.getArrayItem(i);
if (crypt_params.isDictionary() &&
crypt_params.getKey("/Name").isName()) {
QTC::TC("qpdf", "QPDF_encrypt crypt array");
method = interpretCF(encp, crypt_params.getKey("/Name"));
method_source = "stream's Crypt decode parameters (array)";
}
}
}
}
}
}
if (method == e_unknown) {
if ((!encp->encrypt_metadata) && (type == "/Metadata")) {
QTC::TC("qpdf", "QPDF_encryption cleartext metadata");
method = e_none;
} else {
method = encp->cf_stream;
}
}
use_aes = false;
switch (method) {
case e_none:
return;
break;
case e_aes:
use_aes = true;
break;
case e_aesv3:
use_aes = true;
break;
case e_rc4:
break;
default:
// filter local to this stream.
qpdf_for_warning.warn(QPDFExc(
qpdf_e_damaged_pdf,
file->getName(),
"",
file->getLastOffset(),
"unknown encryption filter for streams (check " + method_source +
"); streams may be decrypted improperly"));
// To avoid repeated warnings, reset cf_stream. Assume we'd want to use AES if V == 4.
encp->cf_stream = e_aes;
use_aes = true;
break;
}
}
std::string key = getKeyForObject(encp, og, use_aes);
if (use_aes) {
QTC::TC("qpdf", "QPDF_encryption aes decode stream");
decrypt_pipeline = std::make_unique<Pl_AES_PDF>(
"AES stream decryption",
pipeline,
false,
QUtil::unsigned_char_pointer(key),
key.length());
} else {
QTC::TC("qpdf", "QPDF_encryption rc4 decode stream");
decrypt_pipeline = std::make_unique<Pl_RC4>(
"RC4 stream decryption",
pipeline,
QUtil::unsigned_char_pointer(key),
toI(key.length()));
}
pipeline = decrypt_pipeline.get();
}
void
QPDF::compute_encryption_O_U(
char const* user_password,
char const* owner_password,
int V,
int R,
int key_len,
int P,
bool encrypt_metadata,
std::string const& id1,
std::string& O,
std::string& U)
{
if (V >= 5) {
throw std::logic_error("compute_encryption_O_U called for file with V >= 5");
}
EncryptionData data(V, R, key_len, P, "", "", "", "", "", id1, encrypt_metadata);
data.setO(compute_O_value(user_password, owner_password, data));
O = data.getO();
data.setU(compute_U_value(user_password, data));
U = data.getU();
}
void
QPDF::compute_encryption_parameters_V5(
char const* user_password,
char const* owner_password,
int V,
int R,
int key_len,
int P,
bool encrypt_metadata,
std::string const& id1,
std::string& encryption_key,
std::string& O,
std::string& U,
std::string& OE,
std::string& UE,
std::string& Perms)
{
EncryptionData data(V, R, key_len, P, "", "", "", "", "", id1, encrypt_metadata);
unsigned char k[key_bytes];
QUtil::initializeWithRandomBytes(k, key_bytes);
encryption_key = std::string(reinterpret_cast<char*>(k), key_bytes);
compute_U_UE_value_V5(user_password, encryption_key, data, U, UE);
compute_O_OE_value_V5(owner_password, encryption_key, data, U, O, OE);
Perms = compute_Perms_value_V5(encryption_key, data);
data.setV5EncryptionParameters(O, OE, U, UE, Perms);
}
std::string const&
QPDF::getPaddedUserPassword() const
{
return m->encp->user_password;
}
std::string
QPDF::getTrimmedUserPassword() const
{
std::string result = m->encp->user_password;
trim_user_password(result);
return result;
}
std::string
QPDF::getEncryptionKey() const
{
return m->encp->encryption_key;
}
bool
QPDF::isEncrypted() const
{
return m->encp->encrypted;
}
bool
QPDF::isEncrypted(int& R, int& P)
{
int V;
encryption_method_e stream, string, file;
return isEncrypted(R, P, V, stream, string, file);
}
bool
QPDF::isEncrypted(
int& R,
int& P,
int& V,
encryption_method_e& stream_method,
encryption_method_e& string_method,
encryption_method_e& file_method)
{
if (m->encp->encrypted) {
QPDFObjectHandle trailer = getTrailer();
QPDFObjectHandle encrypt = trailer.getKey("/Encrypt");
QPDFObjectHandle Pkey = encrypt.getKey("/P");
QPDFObjectHandle Rkey = encrypt.getKey("/R");
QPDFObjectHandle Vkey = encrypt.getKey("/V");
P = static_cast<int>(Pkey.getIntValue());
R = Rkey.getIntValueAsInt();
V = Vkey.getIntValueAsInt();
stream_method = m->encp->cf_stream;
string_method = m->encp->cf_string;
file_method = m->encp->cf_file;
return true;
} else {
return false;
}
}
bool
QPDF::ownerPasswordMatched() const
{
return m->encp->owner_password_matched;
}
bool
QPDF::userPasswordMatched() const
{
return m->encp->user_password_matched;
}
static bool
is_bit_set(int P, int bit)
{
// Bits in P are numbered from 1 in the spec
return ((P & (1 << (bit - 1))) != 0);
}
bool
QPDF::allowAccessibility()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
if (R < 3) {
status = is_bit_set(P, 5);
} else {
status = is_bit_set(P, 10);
}
}
return status;
}
bool
QPDF::allowExtractAll()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = is_bit_set(P, 5);
}
return status;
}
bool
QPDF::allowPrintLowRes()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = is_bit_set(P, 3);
}
return status;
}
bool
QPDF::allowPrintHighRes()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = is_bit_set(P, 3);
if ((R >= 3) && (!is_bit_set(P, 12))) {
status = false;
}
}
return status;
}
bool
QPDF::allowModifyAssembly()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
if (R < 3) {
status = is_bit_set(P, 4);
} else {
status = is_bit_set(P, 11);
}
}
return status;
}
bool
QPDF::allowModifyForm()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
if (R < 3) {
status = is_bit_set(P, 6);
} else {
status = is_bit_set(P, 9);
}
}
return status;
}
bool
QPDF::allowModifyAnnotation()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = is_bit_set(P, 6);
}
return status;
}
bool
QPDF::allowModifyOther()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = is_bit_set(P, 4);
}
return status;
}
bool
QPDF::allowModifyAll()
{
int R = 0;
int P = 0;
bool status = true;
if (isEncrypted(R, P)) {
status = (is_bit_set(P, 4) && is_bit_set(P, 6));
if (R >= 3) {
status = status && (is_bit_set(P, 9) && is_bit_set(P, 11));
}
}
return status;
}
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