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import hashlib
import secrets
import struct
from enum import Enum, IntEnum
from typing import Any, Dict, Optional, Tuple, Union, cast
from pypdf._crypt_providers import (
CryptAES,
CryptBase,
CryptIdentity,
CryptRC4,
aes_cbc_decrypt,
aes_cbc_encrypt,
aes_ecb_decrypt,
aes_ecb_encrypt,
rc4_decrypt,
rc4_encrypt,
)
from ._utils import b_, logger_warning
from .generic import (
ArrayObject,
ByteStringObject,
DictionaryObject,
NameObject,
NumberObject,
PdfObject,
StreamObject,
TextStringObject,
create_string_object,
)
class CryptFilter:
def __init__(
self,
stm_crypt: CryptBase,
str_crypt: CryptBase,
ef_crypt: CryptBase,
) -> None:
self.stm_crypt = stm_crypt
self.str_crypt = str_crypt
self.ef_crypt = ef_crypt
def encrypt_object(self, obj: PdfObject) -> PdfObject:
if isinstance(obj, ByteStringObject):
data = self.str_crypt.encrypt(obj.original_bytes)
obj = ByteStringObject(data)
if isinstance(obj, TextStringObject):
data = self.str_crypt.encrypt(obj.get_encoded_bytes())
obj = ByteStringObject(data)
elif isinstance(obj, StreamObject):
obj2 = StreamObject()
obj2.update(obj)
obj2.set_data(self.stm_crypt.encrypt(b_(obj._data)))
for key, value in obj.items(): # Dont forget the Stream dict.
obj2[key] = self.encrypt_object(value)
obj = obj2
elif isinstance(obj, DictionaryObject):
obj2 = DictionaryObject() # type: ignore
for key, value in obj.items():
obj2[key] = self.encrypt_object(value)
obj = obj2
elif isinstance(obj, ArrayObject):
obj = ArrayObject(self.encrypt_object(x) for x in obj)
return obj
def decrypt_object(self, obj: PdfObject) -> PdfObject:
if isinstance(obj, (ByteStringObject, TextStringObject)):
data = self.str_crypt.decrypt(obj.original_bytes)
obj = create_string_object(data)
elif isinstance(obj, StreamObject):
obj._data = self.stm_crypt.decrypt(b_(obj._data))
for key, value in obj.items(): # Dont forget the Stream dict.
obj[key] = self.decrypt_object(value)
elif isinstance(obj, DictionaryObject):
for key, value in obj.items():
obj[key] = self.decrypt_object(value)
elif isinstance(obj, ArrayObject):
for i in range(len(obj)):
obj[i] = self.decrypt_object(obj[i])
return obj
_PADDING = (
b"\x28\xbf\x4e\x5e\x4e\x75\x8a\x41\x64\x00\x4e\x56\xff\xfa\x01\x08"
b"\x2e\x2e\x00\xb6\xd0\x68\x3e\x80\x2f\x0c\xa9\xfe\x64\x53\x69\x7a"
)
def _padding(data: bytes) -> bytes:
return (data + _PADDING)[:32]
class AlgV4:
@staticmethod
def compute_key(
password: bytes,
rev: int,
key_size: int,
o_entry: bytes,
P: int,
id1_entry: bytes,
metadata_encrypted: bool,
) -> bytes:
"""
Algorithm 2: Computing an encryption key.
a) Pad or truncate the password string to exactly 32 bytes. If the
password string is more than 32 bytes long,
use only its first 32 bytes; if it is less than 32 bytes long, pad it
by appending the required number of
additional bytes from the beginning of the following padding string:
< 28 BF 4E 5E 4E 75 8A 41 64 00 4E 56 FF FA 01 08
2E 2E 00 B6 D0 68 3E 80 2F 0C A9 FE 64 53 69 7A >
That is, if the password string is n bytes long, append
the first 32 - n bytes of the padding string to the end
of the password string. If the password string is empty
(zero-length), meaning there is no user password,
substitute the entire padding string in its place.
b) Initialize the MD5 hash function and pass the result of step (a)
as input to this function.
c) Pass the value of the encryption dictionary’s O entry to the
MD5 hash function. ("Algorithm 3: Computing
the encryption dictionary’s O (owner password) value" shows how the
O value is computed.)
d) Convert the integer value of the P entry to a 32-bit unsigned binary
number and pass these bytes to the
MD5 hash function, low-order byte first.
e) Pass the first element of the file’s file identifier array (the value
of the ID entry in the document’s trailer
dictionary; see Table 15) to the MD5 hash function.
f) (Security handlers of revision 4 or greater) If document metadata is
not being encrypted, pass 4 bytes with
the value 0xFFFFFFFF to the MD5 hash function.
g) Finish the hash.
h) (Security handlers of revision 3 or greater) Do the following
50 times: Take the output from the previous
MD5 hash and pass the first n bytes of the output as input into a new
MD5 hash, where n is the number of
bytes of the encryption key as defined by the value of the encryption
dictionary’s Length entry.
i) Set the encryption key to the first n bytes of the output from the
final MD5 hash, where n shall always be 5
for security handlers of revision 2 but, for security handlers of
revision 3 or greater, shall depend on the
value of the encryption dictionary’s Length entry.
Args:
password: The encryption secret as a bytes-string
rev: The encryption revision (see PDF standard)
key_size: The size of the key in bytes
o_entry: The owner entry
P: A set of flags specifying which operations shall be permitted
when the document is opened with user access. If bit 2 is set to 1,
all other bits are ignored and all operations are permitted.
If bit 2 is set to 0, permission for operations are based on the
values of the remaining flags defined in Table 24.
id1_entry:
metadata_encrypted: A boolean indicating if the metadata is encrypted.
Returns:
The u_hash digest of length key_size
"""
a = _padding(password)
u_hash = hashlib.md5(a)
u_hash.update(o_entry)
u_hash.update(struct.pack("<I", P))
u_hash.update(id1_entry)
if rev >= 4 and not metadata_encrypted:
u_hash.update(b"\xff\xff\xff\xff")
u_hash_digest = u_hash.digest()
length = key_size // 8
if rev >= 3:
for _ in range(50):
u_hash_digest = hashlib.md5(u_hash_digest[:length]).digest()
return u_hash_digest[:length]
@staticmethod
def compute_O_value_key(owner_password: bytes, rev: int, key_size: int) -> bytes:
"""
Algorithm 3: Computing the encryption dictionary’s O (owner password) value.
a) Pad or truncate the owner password string as described in step (a)
of "Algorithm 2: Computing an encryption key".
If there is no owner password, use the user password instead.
b) Initialize the MD5 hash function and pass the result of step (a) as
input to this function.
c) (Security handlers of revision 3 or greater) Do the following 50 times:
Take the output from the previous
MD5 hash and pass it as input into a new MD5 hash.
d) Create an RC4 encryption key using the first n bytes of the output
from the final MD5 hash, where n shall
always be 5 for security handlers of revision 2 but, for security
handlers of revision 3 or greater, shall
depend on the value of the encryption dictionary’s Length entry.
e) Pad or truncate the user password string as described in step (a) of
"Algorithm 2: Computing an encryption key".
f) Encrypt the result of step (e), using an RC4 encryption function with
the encryption key obtained in step (d).
g) (Security handlers of revision 3 or greater) Do the following 19 times:
Take the output from the previous
invocation of the RC4 function and pass it as input to a new
invocation of the function; use an encryption
key generated by taking each byte of the encryption key obtained in
step (d) and performing an XOR
(exclusive or) operation between that byte and the single-byte value
of the iteration counter (from 1 to 19).
h) Store the output from the final invocation of the RC4 function as
the value of the O entry in the encryption dictionary.
Args:
owner_password:
rev: The encryption revision (see PDF standard)
key_size: The size of the key in bytes
Returns:
The RC4 key
"""
a = _padding(owner_password)
o_hash_digest = hashlib.md5(a).digest()
if rev >= 3:
for _ in range(50):
o_hash_digest = hashlib.md5(o_hash_digest).digest()
rc4_key = o_hash_digest[: key_size // 8]
return rc4_key
@staticmethod
def compute_O_value(rc4_key: bytes, user_password: bytes, rev: int) -> bytes:
"""
See :func:`compute_O_value_key`.
Args:
rc4_key:
user_password:
rev: The encryption revision (see PDF standard)
Returns:
The RC4 encrypted
"""
a = _padding(user_password)
rc4_enc = rc4_encrypt(rc4_key, a)
if rev >= 3:
for i in range(1, 20):
key = bytes(bytearray(x ^ i for x in rc4_key))
rc4_enc = rc4_encrypt(key, rc4_enc)
return rc4_enc
@staticmethod
def compute_U_value(key: bytes, rev: int, id1_entry: bytes) -> bytes:
"""
Algorithm 4: Computing the encryption dictionary’s U (user password) value.
(Security handlers of revision 2)
a) Create an encryption key based on the user password string, as
described in "Algorithm 2: Computing an encryption key".
b) Encrypt the 32-byte padding string shown in step (a) of
"Algorithm 2: Computing an encryption key", using an RC4 encryption
function with the encryption key from the preceding step.
c) Store the result of step (b) as the value of the U entry in the
encryption dictionary.
Args:
key:
rev: The encryption revision (see PDF standard)
id1_entry:
Returns:
The value
"""
if rev <= 2:
value = rc4_encrypt(key, _PADDING)
return value
"""
Algorithm 5: Computing the encryption dictionary’s U (user password) value.
(Security handlers of revision 3 or greater)
a) Create an encryption key based on the user password string, as
described in "Algorithm 2: Computing an encryption key".
b) Initialize the MD5 hash function and pass the 32-byte padding string
shown in step (a) of "Algorithm 2:
Computing an encryption key" as input to this function.
c) Pass the first element of the file’s file identifier array (the value
of the ID entry in the document’s trailer
dictionary; see Table 15) to the hash function and finish the hash.
d) Encrypt the 16-byte result of the hash, using an RC4 encryption
function with the encryption key from step (a).
e) Do the following 19 times: Take the output from the previous
invocation of the RC4 function and pass it as input to a new
invocation of the function; use an encryption key generated by
taking each byte of the original encryption key obtained in
step (a) and performing an XOR (exclusive or) operation between that
byte and the single-byte value of the iteration counter (from 1 to 19).
f) Append 16 bytes of arbitrary padding to the output from the final
invocation of the RC4 function and store the 32-byte result as the
value of the U entry in the encryption dictionary.
"""
u_hash = hashlib.md5(_PADDING)
u_hash.update(id1_entry)
rc4_enc = rc4_encrypt(key, u_hash.digest())
for i in range(1, 20):
rc4_key = bytes(bytearray(x ^ i for x in key))
rc4_enc = rc4_encrypt(rc4_key, rc4_enc)
return _padding(rc4_enc)
@staticmethod
def verify_user_password(
user_password: bytes,
rev: int,
key_size: int,
o_entry: bytes,
u_entry: bytes,
P: int,
id1_entry: bytes,
metadata_encrypted: bool,
) -> bytes:
"""
Algorithm 6: Authenticating the user password.
a) Perform all but the last step of "Algorithm 4: Computing the
encryption dictionary’s U (user password) value (Security handlers of
revision 2)" or "Algorithm 5: Computing the encryption dictionary’s U
(user password) value (Security handlers of revision 3 or greater)"
using the supplied password string.
b) If the result of step (a) is equal to the value of the encryption
dictionary’s U entry (comparing on the first 16 bytes in the case of
security handlers of revision 3 or greater), the password supplied is
the correct user password. The key obtained in step (a) (that is, in
the first step of "Algorithm 4: Computing the encryption
dictionary’s U (user password) value
(Security handlers of revision 2)" or
"Algorithm 5: Computing the encryption dictionary’s U (user password)
value (Security handlers of revision 3 or greater)") shall be used
to decrypt the document.
Args:
user_password: The user password as a bytes stream
rev: The encryption revision (see PDF standard)
key_size: The size of the key in bytes
o_entry: The owner entry
u_entry: The user entry
P: A set of flags specifying which operations shall be permitted
when the document is opened with user access. If bit 2 is set to 1,
all other bits are ignored and all operations are permitted.
If bit 2 is set to 0, permission for operations are based on the
values of the remaining flags defined in Table 24.
id1_entry:
metadata_encrypted: A boolean indicating if the metadata is encrypted.
Returns:
The key
"""
key = AlgV4.compute_key(
user_password, rev, key_size, o_entry, P, id1_entry, metadata_encrypted
)
u_value = AlgV4.compute_U_value(key, rev, id1_entry)
if rev >= 3:
u_value = u_value[:16]
u_entry = u_entry[:16]
if u_value != u_entry:
key = b""
return key
@staticmethod
def verify_owner_password(
owner_password: bytes,
rev: int,
key_size: int,
o_entry: bytes,
u_entry: bytes,
P: int,
id1_entry: bytes,
metadata_encrypted: bool,
) -> bytes:
"""
Algorithm 7: Authenticating the owner password.
a) Compute an encryption key from the supplied password string, as
described in steps (a) to (d) of
"Algorithm 3: Computing the encryption dictionary’s O (owner password)
value".
b) (Security handlers of revision 2 only) Decrypt the value of the
encryption dictionary’s O entry, using an RC4
encryption function with the encryption key computed in step (a).
(Security handlers of revision 3 or greater) Do the following 20 times:
Decrypt the value of the encryption dictionary’s O entry (first iteration)
or the output from the previous iteration (all subsequent iterations),
using an RC4 encryption function with a different encryption key at
each iteration. The key shall be generated by taking the original key
(obtained in step (a)) and performing an XOR (exclusive or) operation
between each byte of the key and the single-byte value of the
iteration counter (from 19 to 0).
c) The result of step (b) purports to be the user password.
Authenticate this user password using
"Algorithm 6: Authenticating the user password".
If it is correct, the password supplied is the correct owner password.
Args:
owner_password:
rev: The encryption revision (see PDF standard)
key_size: The size of the key in bytes
o_entry: The owner entry
u_entry: The user entry
P: A set of flags specifying which operations shall be permitted
when the document is opened with user access. If bit 2 is set to 1,
all other bits are ignored and all operations are permitted.
If bit 2 is set to 0, permission for operations are based on the
values of the remaining flags defined in Table 24.
id1_entry:
metadata_encrypted: A boolean indicating if the metadata is encrypted.
Returns:
bytes
"""
rc4_key = AlgV4.compute_O_value_key(owner_password, rev, key_size)
if rev <= 2:
user_password = rc4_decrypt(rc4_key, o_entry)
else:
user_password = o_entry
for i in range(19, -1, -1):
key = bytes(bytearray(x ^ i for x in rc4_key))
user_password = rc4_decrypt(key, user_password)
return AlgV4.verify_user_password(
user_password,
rev,
key_size,
o_entry,
u_entry,
P,
id1_entry,
metadata_encrypted,
)
class AlgV5:
@staticmethod
def verify_owner_password(
R: int, password: bytes, o_value: bytes, oe_value: bytes, u_value: bytes
) -> bytes:
"""
Algorithm 3.2a Computing an encryption key.
To understand the algorithm below, it is necessary to treat the O and U
strings in the Encrypt dictionary as made up of three sections.
The first 32 bytes are a hash value (explained below). The next 8 bytes
are called the Validation Salt. The final 8 bytes are called the Key Salt.
1. The password string is generated from Unicode input by processing the
input string with the SASLprep (IETF RFC 4013) profile of
stringprep (IETF RFC 3454), and then converting to a UTF-8
representation.
2. Truncate the UTF-8 representation to 127 bytes if it is longer than
127 bytes.
3. Test the password against the owner key by computing the SHA-256 hash
of the UTF-8 password concatenated with the 8 bytes of owner
Validation Salt, concatenated with the 48-byte U string. If the
32-byte result matches the first 32 bytes of the O string, this is
the owner password.
Compute an intermediate owner key by computing the SHA-256 hash of
the UTF-8 password concatenated with the 8 bytes of owner Key Salt,
concatenated with the 48-byte U string. The 32-byte result is the
key used to decrypt the 32-byte OE string using AES-256 in CBC mode
with no padding and an initialization vector of zero.
The 32-byte result is the file encryption key.
4. Test the password against the user key by computing the SHA-256 hash
of the UTF-8 password concatenated with the 8 bytes of user
Validation Salt. If the 32 byte result matches the first 32 bytes of
the U string, this is the user password.
Compute an intermediate user key by computing the SHA-256 hash of the
UTF-8 password concatenated with the 8 bytes of user Key Salt.
The 32-byte result is the key used to decrypt the 32-byte
UE string using AES-256 in CBC mode with no padding and an
initialization vector of zero. The 32-byte result is the file
encryption key.
5. Decrypt the 16-byte Perms string using AES-256 in ECB mode with an
initialization vector of zero and the file encryption key as the key.
Verify that bytes 9-11 of the result are the characters ‘a’, ‘d’, ‘b’.
Bytes 0-3 of the decrypted Perms entry, treated as a little-endian
integer, are the user permissions.
They should match the value in the P key.
Args:
R: A number specifying which revision of the standard security
handler shall be used to interpret this dictionary
password: The owner password
o_value: A 32-byte string, based on both the owner and user passwords,
that shall be used in computing the encryption key and in
determining whether a valid owner password was entered
oe_value:
u_value: A 32-byte string, based on the user password, that shall be
used in determining whether to prompt the user for a password and,
if so, whether a valid user or owner password was entered.
Returns:
The key
"""
password = password[:127]
if (
AlgV5.calculate_hash(R, password, o_value[32:40], u_value[:48])
!= o_value[:32]
):
return b""
iv = bytes(0 for _ in range(16))
tmp_key = AlgV5.calculate_hash(R, password, o_value[40:48], u_value[:48])
key = aes_cbc_decrypt(tmp_key, iv, oe_value)
return key
@staticmethod
def verify_user_password(
R: int, password: bytes, u_value: bytes, ue_value: bytes
) -> bytes:
"""
See :func:`verify_owner_password`.
Args:
R: A number specifying which revision of the standard security
handler shall be used to interpret this dictionary
password: The user password
u_value: A 32-byte string, based on the user password, that shall be
used in determining whether to prompt the user for a password
and, if so, whether a valid user or owner password was entered.
ue_value:
Returns:
bytes
"""
password = password[:127]
if AlgV5.calculate_hash(R, password, u_value[32:40], b"") != u_value[:32]:
return b""
iv = bytes(0 for _ in range(16))
tmp_key = AlgV5.calculate_hash(R, password, u_value[40:48], b"")
return aes_cbc_decrypt(tmp_key, iv, ue_value)
@staticmethod
def calculate_hash(R: int, password: bytes, salt: bytes, udata: bytes) -> bytes:
# from https://github.com/qpdf/qpdf/blob/main/libqpdf/QPDF_encryption.cc
k = hashlib.sha256(password + salt + udata).digest()
if R < 6:
return k
count = 0
while True:
count += 1
k1 = password + k + udata
e = aes_cbc_encrypt(k[:16], k[16:32], k1 * 64)
hash_fn = (
hashlib.sha256,
hashlib.sha384,
hashlib.sha512,
)[sum(e[:16]) % 3]
k = hash_fn(e).digest()
if count >= 64 and e[-1] <= count - 32:
break
return k[:32]
@staticmethod
def verify_perms(
key: bytes, perms: bytes, p: int, metadata_encrypted: bool
) -> bool:
"""
See :func:`verify_owner_password` and :func:`compute_perms_value`.
Args:
key: The owner password
perms:
p: A set of flags specifying which operations shall be permitted
when the document is opened with user access.
If bit 2 is set to 1, all other bits are ignored and all
operations are permitted.
If bit 2 is set to 0, permission for operations are based on
the values of the remaining flags defined in Table 24.
metadata_encrypted:
Returns:
A boolean
"""
b8 = b"T" if metadata_encrypted else b"F"
p1 = struct.pack("<I", p) + b"\xff\xff\xff\xff" + b8 + b"adb"
p2 = aes_ecb_decrypt(key, perms)
return p1 == p2[:12]
@staticmethod
def generate_values(
R: int,
user_password: bytes,
owner_password: bytes,
key: bytes,
p: int,
metadata_encrypted: bool,
) -> Dict[Any, Any]:
user_password = user_password[:127]
owner_password = owner_password[:127]
u_value, ue_value = AlgV5.compute_U_value(R, user_password, key)
o_value, oe_value = AlgV5.compute_O_value(R, owner_password, key, u_value)
perms = AlgV5.compute_Perms_value(key, p, metadata_encrypted)
return {
"/U": u_value,
"/UE": ue_value,
"/O": o_value,
"/OE": oe_value,
"/Perms": perms,
}
@staticmethod
def compute_U_value(R: int, password: bytes, key: bytes) -> Tuple[bytes, bytes]:
"""
Algorithm 3.8 Computing the encryption dictionary’s U (user password)
and UE (user encryption key) values.
1. Generate 16 random bytes of data using a strong random number generator.
The first 8 bytes are the User Validation Salt. The second 8 bytes
are the User Key Salt. Compute the 32-byte SHA-256 hash of the
password concatenated with the User Validation Salt. The 48-byte
string consisting of the 32-byte hash followed by the User
Validation Salt followed by the User Key Salt is stored as the U key.
2. Compute the 32-byte SHA-256 hash of the password concatenated with
the User Key Salt. Using this hash as the key, encrypt the file
encryption key using AES-256 in CBC mode with no padding and an
initialization vector of zero. The resulting 32-byte string is stored
as the UE key.
Args:
R:
password:
key:
Returns:
A tuple (u-value, ue value)
"""
random_bytes = secrets.token_bytes(16)
val_salt = random_bytes[:8]
key_salt = random_bytes[8:]
u_value = AlgV5.calculate_hash(R, password, val_salt, b"") + val_salt + key_salt
tmp_key = AlgV5.calculate_hash(R, password, key_salt, b"")
iv = bytes(0 for _ in range(16))
ue_value = aes_cbc_encrypt(tmp_key, iv, key)
return u_value, ue_value
@staticmethod
def compute_O_value(
R: int, password: bytes, key: bytes, u_value: bytes
) -> Tuple[bytes, bytes]:
"""
Algorithm 3.9 Computing the encryption dictionary’s O (owner password)
and OE (owner encryption key) values.
1. Generate 16 random bytes of data using a strong random number
generator. The first 8 bytes are the Owner Validation Salt. The
second 8 bytes are the Owner Key Salt. Compute the 32-byte SHA-256
hash of the password concatenated with the Owner Validation Salt and
then concatenated with the 48-byte U string as generated in
Algorithm 3.8. The 48-byte string consisting of the 32-byte hash
followed by the Owner Validation Salt followed by the Owner Key Salt
is stored as the O key.
2. Compute the 32-byte SHA-256 hash of the password concatenated with
the Owner Key Salt and then concatenated with the 48-byte U string as
generated in Algorithm 3.8. Using this hash as the key,
encrypt the file encryption key using AES-256 in CBC mode with
no padding and an initialization vector of zero.
The resulting 32-byte string is stored as the OE key.
Args:
R:
password:
key:
u_value: A 32-byte string, based on the user password, that shall be
used in determining whether to prompt the user for a password
and, if so, whether a valid user or owner password was entered.
Returns:
A tuple (O value, OE value)
"""
random_bytes = secrets.token_bytes(16)
val_salt = random_bytes[:8]
key_salt = random_bytes[8:]
o_value = (
AlgV5.calculate_hash(R, password, val_salt, u_value) + val_salt + key_salt
)
tmp_key = AlgV5.calculate_hash(R, password, key_salt, u_value[:48])
iv = bytes(0 for _ in range(16))
oe_value = aes_cbc_encrypt(tmp_key, iv, key)
return o_value, oe_value
@staticmethod
def compute_Perms_value(key: bytes, p: int, metadata_encrypted: bool) -> bytes:
"""
Algorithm 3.10 Computing the encryption dictionary’s Perms
(permissions) value.
1. Extend the permissions (contents of the P integer) to 64 bits by
setting the upper 32 bits to all 1’s.
(This allows for future extension without changing the format.)
2. Record the 8 bytes of permission in the bytes 0-7 of the block,
low order byte first.
3. Set byte 8 to the ASCII value ' T ' or ' F ' according to the
EncryptMetadata Boolean.
4. Set bytes 9-11 to the ASCII characters ' a ', ' d ', ' b '.
5. Set bytes 12-15 to 4 bytes of random data, which will be ignored.
6. Encrypt the 16-byte block using AES-256 in ECB mode with an
initialization vector of zero, using the file encryption key as the
key. The result (16 bytes) is stored as the Perms string, and checked
for validity when the file is opened.
Args:
key:
p: A set of flags specifying which operations shall be permitted
when the document is opened with user access. If bit 2 is set to 1,
all other bits are ignored and all operations are permitted.
If bit 2 is set to 0, permission for operations are based on the
values of the remaining flags defined in Table 24.
metadata_encrypted: A boolean indicating if the metadata is encrypted.
Returns:
The perms value
"""
b8 = b"T" if metadata_encrypted else b"F"
rr = secrets.token_bytes(4)
data = struct.pack("<I", p) + b"\xff\xff\xff\xff" + b8 + b"adb" + rr
perms = aes_ecb_encrypt(key, data)
return perms
[docs]class PasswordType(IntEnum):
NOT_DECRYPTED = 0
USER_PASSWORD = 1
OWNER_PASSWORD = 2
class EncryptAlgorithm(tuple, Enum): # type: ignore # noqa: SLOT001
# V, R, Length
RC4_40 = (1, 2, 40)
RC4_128 = (2, 3, 128)
AES_128 = (4, 4, 128)
AES_256_R5 = (5, 5, 256)
AES_256 = (5, 6, 256)
class EncryptionValues:
O: bytes # noqa
U: bytes
OE: bytes
UE: bytes
Perms: bytes
class Encryption:
"""
Collects and manages parameters for PDF document encryption and decryption.
Args:
V: A code specifying the algorithm to be used in encrypting and
decrypting the document.
R: The revision of the standard security handler.
Length: The length of the encryption key in bits.
P: A set of flags specifying which operations shall be permitted
when the document is opened with user access
entry: The encryption dictionary object.
EncryptMetadata: Whether to encrypt metadata in the document.
first_id_entry: The first 16 bytes of the file's original ID.
StmF: The name of the crypt filter that shall be used by default
when decrypting streams.
StrF: The name of the crypt filter that shall be used when decrypting
all strings in the document.
EFF: The name of the crypt filter that shall be used when
encrypting embedded file streams that do not have their own
crypt filter specifier.
values: Additional encryption parameters.
"""
def __init__(
self,
V: int,
R: int,
Length: int,
P: int,
entry: DictionaryObject,
EncryptMetadata: bool,
first_id_entry: bytes,
StmF: str,
StrF: str,
EFF: str,
values: Optional[EncryptionValues],
) -> None:
# See TABLE 3.18 Entries common to all encryption dictionaries
# use same name as keys of encryption dictionaries entries
self.V = V
self.R = R
self.Length = Length # key_size
self.P = (P + 0x100000000) % 0x100000000 # maybe P < 0
self.EncryptMetadata = EncryptMetadata
self.id1_entry = first_id_entry
self.StmF = StmF
self.StrF = StrF
self.EFF = EFF
self.values: EncryptionValues = values if values else EncryptionValues()
self._password_type = PasswordType.NOT_DECRYPTED
self._key: Optional[bytes] = None
def is_decrypted(self) -> bool:
return self._password_type != PasswordType.NOT_DECRYPTED
def encrypt_object(self, obj: PdfObject, idnum: int, generation: int) -> PdfObject:
# skip calculate key
if not self._is_encryption_object(obj):
return obj
cf = self._make_crypt_filter(idnum, generation)
return cf.encrypt_object(obj)
def decrypt_object(self, obj: PdfObject, idnum: int, generation: int) -> PdfObject:
# skip calculate key
if not self._is_encryption_object(obj):
return obj
cf = self._make_crypt_filter(idnum, generation)
return cf.decrypt_object(obj)
@staticmethod
def _is_encryption_object(obj: PdfObject) -> bool:
return isinstance(
obj,
(
ByteStringObject,
TextStringObject,
StreamObject,
ArrayObject,
DictionaryObject,
),
)
def _make_crypt_filter(self, idnum: int, generation: int) -> CryptFilter:
"""
Algorithm 1: Encryption of data using the RC4 or AES algorithms.
a) Obtain the object number and generation number from the object
identifier of the string or stream to be encrypted
(see 7.3.10, "Indirect Objects"). If the string is a direct object,
use the identifier of the indirect object containing it.
b) For all strings and streams without crypt filter specifier; treating
the object number and generation number as binary integers, extend
the original n-byte encryption key to n + 5 bytes by appending the
low-order 3 bytes of the object number and the low-order 2 bytes of
the generation number in that order, low-order byte first.
(n is 5 unless the value of V in the encryption dictionary is greater
than 1, in which case n is the value of Length divided by 8.)
If using the AES algorithm, extend the encryption key an additional
4 bytes by adding the value “sAlT”, which corresponds to the
hexadecimal values 0x73, 0x41, 0x6C, 0x54. (This addition is done for
backward compatibility and is not intended to provide additional
security.)
c) Initialize the MD5 hash function and pass the result of step (b) as
input to this function.
d) Use the first (n + 5) bytes, up to a maximum of 16, of the output
from the MD5 hash as the key for the RC4 or AES symmetric key
algorithms, along with the string or stream data to be encrypted.
If using the AES algorithm, the Cipher Block Chaining (CBC) mode,
which requires an initialization vector, is used. The block size
parameter is set to 16 bytes, and the initialization vector is a
16-byte random number that is stored as the first 16 bytes of the
encrypted stream or string.
Algorithm 3.1a Encryption of data using the AES algorithm
1. Use the 32-byte file encryption key for the AES-256 symmetric key
algorithm, along with the string or stream data to be encrypted.
Use the AES algorithm in Cipher Block Chaining (CBC) mode, which
requires an initialization vector. The block size parameter is set to
16 bytes, and the initialization vector is a 16-byte random number
that is stored as the first 16 bytes of the encrypted stream or string.
The output is the encrypted data to be stored in the PDF file.
"""
pack1 = struct.pack("<i", idnum)[:3]
pack2 = struct.pack("<i", generation)[:2]
assert self._key
key = self._key
n = 5 if self.V == 1 else self.Length // 8
key_data = key[:n] + pack1 + pack2
key_hash = hashlib.md5(key_data)
rc4_key = key_hash.digest()[: min(n + 5, 16)]
# for AES-128
key_hash.update(b"sAlT")
aes128_key = key_hash.digest()[: min(n + 5, 16)]
# for AES-256
aes256_key = key
stm_crypt = self._get_crypt(self.StmF, rc4_key, aes128_key, aes256_key)
str_crypt = self._get_crypt(self.StrF, rc4_key, aes128_key, aes256_key)
ef_crypt = self._get_crypt(self.EFF, rc4_key, aes128_key, aes256_key)
return CryptFilter(stm_crypt, str_crypt, ef_crypt)
@staticmethod
def _get_crypt(
method: str, rc4_key: bytes, aes128_key: bytes, aes256_key: bytes
) -> CryptBase:
if method == "/AESV3":
return CryptAES(aes256_key)
if method == "/AESV2":
return CryptAES(aes128_key)
elif method == "/Identity":
return CryptIdentity()
else:
return CryptRC4(rc4_key)
@staticmethod
def _encode_password(password: Union[bytes, str]) -> bytes:
if isinstance(password, str):
try:
pwd = password.encode("latin-1")
except Exception:
pwd = password.encode("utf-8")
else:
pwd = password
return pwd
def verify(self, password: Union[bytes, str]) -> PasswordType:
pwd = self._encode_password(password)
key, rc = self.verify_v4(pwd) if self.V <= 4 else self.verify_v5(pwd)
if rc != PasswordType.NOT_DECRYPTED:
self._password_type = rc
self._key = key
return rc
def verify_v4(self, password: bytes) -> Tuple[bytes, PasswordType]:
# verify owner password first
key = AlgV4.verify_owner_password(
password,
self.R,
self.Length,
self.values.O,
self.values.U,
self.P,
self.id1_entry,
self.EncryptMetadata,
)
if key:
return key, PasswordType.OWNER_PASSWORD
key = AlgV4.verify_user_password(
password,
self.R,
self.Length,
self.values.O,
self.values.U,
self.P,
self.id1_entry,
self.EncryptMetadata,
)
if key:
return key, PasswordType.USER_PASSWORD
return b"", PasswordType.NOT_DECRYPTED
def verify_v5(self, password: bytes) -> Tuple[bytes, PasswordType]:
# TODO: use SASLprep process
# verify owner password first
key = AlgV5.verify_owner_password(
self.R, password, self.values.O, self.values.OE, self.values.U
)
rc = PasswordType.OWNER_PASSWORD
if not key:
key = AlgV5.verify_user_password(
self.R, password, self.values.U, self.values.UE
)
rc = PasswordType.USER_PASSWORD
if not key:
return b"", PasswordType.NOT_DECRYPTED
# verify Perms
if not AlgV5.verify_perms(key, self.values.Perms, self.P, self.EncryptMetadata):
logger_warning("ignore '/Perms' verify failed", __name__)
return key, rc
def write_entry(
self, user_password: str, owner_password: Optional[str]
) -> DictionaryObject:
user_pwd = self._encode_password(user_password)
owner_pwd = self._encode_password(owner_password) if owner_password else None
if owner_pwd is None:
owner_pwd = user_pwd
if self.V <= 4:
self.compute_values_v4(user_pwd, owner_pwd)
else:
self._key = secrets.token_bytes(self.Length // 8)
values = AlgV5.generate_values(
self.R, user_pwd, owner_pwd, self._key, self.P, self.EncryptMetadata
)
self.values.O = values["/O"]
self.values.U = values["/U"]
self.values.OE = values["/OE"]
self.values.UE = values["/UE"]
self.values.Perms = values["/Perms"]
dict_obj = DictionaryObject()
dict_obj[NameObject("/V")] = NumberObject(self.V)
dict_obj[NameObject("/R")] = NumberObject(self.R)
dict_obj[NameObject("/Length")] = NumberObject(self.Length)
dict_obj[NameObject("/P")] = NumberObject(self.P)
dict_obj[NameObject("/Filter")] = NameObject("/Standard")
# ignore /EncryptMetadata
dict_obj[NameObject("/O")] = ByteStringObject(self.values.O)
dict_obj[NameObject("/U")] = ByteStringObject(self.values.U)
if self.V >= 4:
# TODO: allow different method
std_cf = DictionaryObject()
std_cf[NameObject("/AuthEvent")] = NameObject("/DocOpen")
std_cf[NameObject("/CFM")] = NameObject(self.StmF)
std_cf[NameObject("/Length")] = NumberObject(self.Length // 8)
cf = DictionaryObject()
cf[NameObject("/StdCF")] = std_cf
dict_obj[NameObject("/CF")] = cf
dict_obj[NameObject("/StmF")] = NameObject("/StdCF")
dict_obj[NameObject("/StrF")] = NameObject("/StdCF")
# ignore EFF
# dict_obj[NameObject("/EFF")] = NameObject("/StdCF")
if self.V >= 5:
dict_obj[NameObject("/OE")] = ByteStringObject(self.values.OE)
dict_obj[NameObject("/UE")] = ByteStringObject(self.values.UE)
dict_obj[NameObject("/Perms")] = ByteStringObject(self.values.Perms)
return dict_obj
def compute_values_v4(self, user_password: bytes, owner_password: bytes) -> None:
rc4_key = AlgV4.compute_O_value_key(owner_password, self.R, self.Length)
o_value = AlgV4.compute_O_value(rc4_key, user_password, self.R)
key = AlgV4.compute_key(
user_password,
self.R,
self.Length,
o_value,
self.P,
self.id1_entry,
self.EncryptMetadata,
)
u_value = AlgV4.compute_U_value(key, self.R, self.id1_entry)
self._key = key
self.values.O = o_value
self.values.U = u_value
@staticmethod
def read(encryption_entry: DictionaryObject, first_id_entry: bytes) -> "Encryption":
if encryption_entry.get("/Filter") != "/Standard":
raise NotImplementedError(
"only Standard PDF encryption handler is available"
)
if "/SubFilter" in encryption_entry:
raise NotImplementedError("/SubFilter NOT supported")
stm_filter = "/V2"
str_filter = "/V2"
ef_filter = "/V2"
alg_ver = encryption_entry.get("/V", 0)
if alg_ver not in (1, 2, 3, 4, 5):
raise NotImplementedError(f"Encryption V={alg_ver} NOT supported")
if alg_ver >= 4:
filters = encryption_entry["/CF"]
stm_filter = encryption_entry.get("/StmF", "/Identity")
str_filter = encryption_entry.get("/StrF", "/Identity")
ef_filter = encryption_entry.get("/EFF", stm_filter)
if stm_filter != "/Identity":
stm_filter = filters[stm_filter]["/CFM"] # type: ignore
if str_filter != "/Identity":
str_filter = filters[str_filter]["/CFM"] # type: ignore
if ef_filter != "/Identity":
ef_filter = filters[ef_filter]["/CFM"] # type: ignore
allowed_methods = ("/Identity", "/V2", "/AESV2", "/AESV3")
if stm_filter not in allowed_methods:
raise NotImplementedError(f"StmF Method {stm_filter} NOT supported!")
if str_filter not in allowed_methods:
raise NotImplementedError(f"StrF Method {str_filter} NOT supported!")
if ef_filter not in allowed_methods:
raise NotImplementedError(f"EFF Method {ef_filter} NOT supported!")
alg_rev = cast(int, encryption_entry["/R"])
perm_flags = cast(int, encryption_entry["/P"])
key_bits = encryption_entry.get("/Length", 40)
encrypt_metadata = encryption_entry.get("/EncryptMetadata")
encrypt_metadata = (
encrypt_metadata.value if encrypt_metadata is not None else True
)
values = EncryptionValues()
values.O = cast(ByteStringObject, encryption_entry["/O"]).original_bytes
values.U = cast(ByteStringObject, encryption_entry["/U"]).original_bytes
values.OE = encryption_entry.get("/OE", ByteStringObject()).original_bytes
values.UE = encryption_entry.get("/UE", ByteStringObject()).original_bytes
values.Perms = encryption_entry.get("/Perms", ByteStringObject()).original_bytes
return Encryption(
V=alg_ver,
R=alg_rev,
Length=key_bits,
P=perm_flags,
EncryptMetadata=encrypt_metadata,
first_id_entry=first_id_entry,
values=values,
StrF=str_filter,
StmF=stm_filter,
EFF=ef_filter,
entry=encryption_entry, # Dummy entry for the moment; will get removed
)
@staticmethod
def make(
alg: EncryptAlgorithm, permissions: int, first_id_entry: bytes
) -> "Encryption":
alg_ver, alg_rev, key_bits = alg
stm_filter, str_filter, ef_filter = "/V2", "/V2", "/V2"
if alg == EncryptAlgorithm.AES_128:
stm_filter, str_filter, ef_filter = "/AESV2", "/AESV2", "/AESV2"
elif alg in (EncryptAlgorithm.AES_256_R5, EncryptAlgorithm.AES_256):
stm_filter, str_filter, ef_filter = "/AESV3", "/AESV3", "/AESV3"
return Encryption(
V=alg_ver,
R=alg_rev,
Length=key_bits,
P=permissions,
EncryptMetadata=True,
first_id_entry=first_id_entry,
values=None,
StrF=str_filter,
StmF=stm_filter,
EFF=ef_filter,
entry=DictionaryObject(), # Dummy entry for the moment; will get removed
)