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import hashlib
import random
import struct
from enum import IntEnum
from typing import Any, Dict, Optional, Tuple, Union, cast
from ._utils import logger_warning
from .errors import DependencyError
from .generic import (
ArrayObject,
ByteStringObject,
DictionaryObject,
PdfObject,
StreamObject,
TextStringObject,
create_string_object,
)
class CryptBase:
def encrypt(self, data: bytes) -> bytes: # pragma: no cover
return data
def decrypt(self, data: bytes) -> bytes: # pragma: no cover
return data
class CryptIdentity(CryptBase):
pass
try:
from Crypto.Cipher import AES, ARC4 # type: ignore[import]
from Crypto.Util.Padding import pad # type: ignore[import]
class CryptRC4(CryptBase):
def __init__(self, key: bytes) -> None:
self.key = key
def encrypt(self, data: bytes) -> bytes:
return ARC4.ARC4Cipher(self.key).encrypt(data)
def decrypt(self, data: bytes) -> bytes:
return ARC4.ARC4Cipher(self.key).decrypt(data)
class CryptAES(CryptBase):
def __init__(self, key: bytes) -> None:
self.key = key
def encrypt(self, data: bytes) -> bytes:
iv = bytes(bytearray(random.randint(0, 255) for _ in range(16)))
p = 16 - len(data) % 16
data += bytes(bytearray(p for _ in range(p)))
aes = AES.new(self.key, AES.MODE_CBC, iv)
return iv + aes.encrypt(data)
def decrypt(self, data: bytes) -> bytes:
iv = data[:16]
data = data[16:]
aes = AES.new(self.key, AES.MODE_CBC, iv)
if len(data) % 16:
data = pad(data, 16)
d = aes.decrypt(data)
if len(d) == 0:
return d
else:
return d[: -d[-1]]
def RC4_encrypt(key: bytes, data: bytes) -> bytes:
return ARC4.ARC4Cipher(key).encrypt(data)
def RC4_decrypt(key: bytes, data: bytes) -> bytes:
return ARC4.ARC4Cipher(key).decrypt(data)
def AES_ECB_encrypt(key: bytes, data: bytes) -> bytes:
return AES.new(key, AES.MODE_ECB).encrypt(data)
def AES_ECB_decrypt(key: bytes, data: bytes) -> bytes:
return AES.new(key, AES.MODE_ECB).decrypt(data)
def AES_CBC_encrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
return AES.new(key, AES.MODE_CBC, iv).encrypt(data)
def AES_CBC_decrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
return AES.new(key, AES.MODE_CBC, iv).decrypt(data)
except ImportError:
class CryptRC4(CryptBase): # type: ignore
def __init__(self, key: bytes) -> None:
self.S = list(range(256))
j = 0
for i in range(256):
j = (j + self.S[i] + key[i % len(key)]) % 256
self.S[i], self.S[j] = self.S[j], self.S[i]
def encrypt(self, data: bytes) -> bytes:
S = list(self.S)
out = list(0 for _ in range(len(data)))
i, j = 0, 0
for k in range(len(data)):
i = (i + 1) % 256
j = (j + S[i]) % 256
S[i], S[j] = S[j], S[i]
x = S[(S[i] + S[j]) % 256]
out[k] = data[k] ^ x
return bytes(bytearray(out))
def decrypt(self, data: bytes) -> bytes:
return self.encrypt(data)
class CryptAES(CryptBase): # type: ignore
def __init__(self, key: bytes) -> None:
pass
def encrypt(self, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
def decrypt(self, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
def RC4_encrypt(key: bytes, data: bytes) -> bytes:
return CryptRC4(key).encrypt(data)
def RC4_decrypt(key: bytes, data: bytes) -> bytes:
return CryptRC4(key).decrypt(data)
def AES_ECB_encrypt(key: bytes, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
def AES_ECB_decrypt(key: bytes, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
def AES_CBC_encrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
def AES_CBC_decrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
raise DependencyError("PyCryptodome is required for AES algorithm")
class CryptFilter:
def __init__(
self, stmCrypt: CryptBase, strCrypt: CryptBase, efCrypt: CryptBase
) -> None:
self.stmCrypt = stmCrypt
self.strCrypt = strCrypt
self.efCrypt = efCrypt
def encrypt_object(self, obj: PdfObject) -> PdfObject:
# TODO
return NotImplemented
def decrypt_object(self, obj: PdfObject) -> PdfObject:
if isinstance(obj, (ByteStringObject, TextStringObject)):
data = self.strCrypt.decrypt(obj.original_bytes)
obj = create_string_object(data)
elif isinstance(obj, StreamObject):
obj._data = self.stmCrypt.decrypt(obj._data)
elif isinstance(obj, DictionaryObject):
for dictkey, value in list(obj.items()):
obj[dictkey] = self.decrypt_object(value)
elif isinstance(obj, ArrayObject):
for i in range(len(obj)):
obj[i] = self.decrypt_object(obj[i])
return obj
_PADDING = bytes(
[
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,
]
)
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.
"""
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 metadata_encrypted is False:
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.
"""
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`."""
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.
"""
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.
"""
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.
"""
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.
"""
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`."""
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`."""
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(
user_password: bytes,
owner_password: bytes,
key: bytes,
p: int,
metadata_encrypted: bool,
) -> Dict[Any, Any]:
u_value, ue_value = AlgV5.compute_U_value(user_password, key)
o_value, oe_value = AlgV5.compute_O_value(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(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.
"""
random_bytes = bytes(random.randrange(0, 256) for _ in range(16))
val_salt = random_bytes[:8]
key_salt = random_bytes[8:]
u_value = hashlib.sha256(password + val_salt).digest() + val_salt + key_salt
tmp_key = hashlib.sha256(password + key_salt).digest()
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(
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.
"""
random_bytes = bytes(random.randrange(0, 256) for _ in range(16))
val_salt = random_bytes[:8]
key_salt = random_bytes[8:]
o_value = (
hashlib.sha256(password + val_salt + u_value).digest() + val_salt + key_salt
)
tmp_key = hashlib.sha256(password + key_salt + u_value).digest()
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.
"""
b8 = b"T" if metadata_encrypted else b"F"
rr = bytes(random.randrange(0, 256) for _ in range(4))
data = struct.pack("<I", p) + b"\xff\xff\xff\xff" + b8 + b"adb" + rr
perms = AES_ECB_encrypt(key, data)
return perms
class PasswordType(IntEnum):
NOT_DECRYPTED = 0
USER_PASSWORD = 1
OWNER_PASSWORD = 2
class Encryption:
def __init__(
self,
algV: int,
algR: int,
entry: DictionaryObject,
first_id_entry: bytes,
StmF: str,
StrF: str,
EFF: str,
) -> None:
# See TABLE 3.18 Entries common to all encryption dictionaries
self.algV = algV
self.algR = algR
self.entry = entry
self.key_size = entry.get("/Length", 40)
self.id1_entry = first_id_entry
self.StmF = StmF
self.StrF = StrF
self.EFF = EFF
# 1 => owner password
# 2 => user password
self._password_type = PasswordType.NOT_DECRYPTED
self._key: Optional[bytes] = None
def is_decrypted(self) -> bool:
return self._password_type != PasswordType.NOT_DECRYPTED
def decrypt_object(self, obj: PdfObject, idnum: int, generation: int) -> PdfObject:
"""
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.algV == 1 else self.key_size // 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
stmCrypt = self._get_crypt(self.StmF, rc4_key, aes128_key, aes256_key)
StrCrypt = self._get_crypt(self.StrF, rc4_key, aes128_key, aes256_key)
efCrypt = self._get_crypt(self.EFF, rc4_key, aes128_key, aes256_key)
cf = CryptFilter(stmCrypt, StrCrypt, efCrypt)
return cf.decrypt_object(obj)
@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)
def verify(self, password: Union[bytes, str]) -> PasswordType:
if isinstance(password, str):
try:
pwd = password.encode("latin-1")
except Exception: # noqa
pwd = password.encode("utf-8")
else:
pwd = password
key, rc = self.verify_v4(pwd) if self.algV <= 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]:
R = cast(int, self.entry["/R"])
P = cast(int, self.entry["/P"])
P = (P + 0x100000000) % 0x100000000 # maybe < 0
# make type(metadata_encrypted) == bool
em = self.entry.get("/EncryptMetadata")
metadata_encrypted = em.value if em else True
o_entry = cast(ByteStringObject, self.entry["/O"].get_object()).original_bytes
u_entry = cast(ByteStringObject, self.entry["/U"].get_object()).original_bytes
# verify owner password first
key = AlgV4.verify_owner_password(
password,
R,
self.key_size,
o_entry,
u_entry,
P,
self.id1_entry,
metadata_encrypted,
)
if key:
return key, PasswordType.OWNER_PASSWORD
key = AlgV4.verify_user_password(
password,
R,
self.key_size,
o_entry,
u_entry,
P,
self.id1_entry,
metadata_encrypted,
)
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
o_entry = cast(ByteStringObject, self.entry["/O"].get_object()).original_bytes
u_entry = cast(ByteStringObject, self.entry["/U"].get_object()).original_bytes
oe_entry = cast(ByteStringObject, self.entry["/OE"].get_object()).original_bytes
ue_entry = cast(ByteStringObject, self.entry["/UE"].get_object()).original_bytes
# verify owner password first
key = AlgV5.verify_owner_password(
self.algR, password, o_entry, oe_entry, u_entry
)
rc = PasswordType.OWNER_PASSWORD
if not key:
key = AlgV5.verify_user_password(self.algR, password, u_entry, ue_entry)
rc = PasswordType.USER_PASSWORD
if not key:
return b"", PasswordType.NOT_DECRYPTED
# verify Perms
perms = cast(ByteStringObject, self.entry["/Perms"].get_object()).original_bytes
P = cast(int, self.entry["/P"])
P = (P + 0x100000000) % 0x100000000 # maybe < 0
metadata_encrypted = self.entry.get("/EncryptMetadata", True)
if not AlgV5.verify_perms(key, perms, P, metadata_encrypted):
logger_warning("ignore '/Perms' verify failed", __name__)
return key, rc
@staticmethod
def read(encryption_entry: DictionaryObject, first_id_entry: bytes) -> "Encryption":
filter = encryption_entry.get("/Filter")
if filter != "/Standard":
raise NotImplementedError(
"only Standard PDF encryption handler is available"
)
if "/SubFilter" in encryption_entry:
raise NotImplementedError("/SubFilter NOT supported")
StmF = "/V2"
StrF = "/V2"
EFF = "/V2"
V = encryption_entry.get("/V", 0)
if V not in (1, 2, 3, 4, 5):
raise NotImplementedError(f"Encryption V={V} NOT supported")
if V >= 4:
filters = encryption_entry["/CF"]
StmF = encryption_entry.get("/StmF", "/Identity")
StrF = encryption_entry.get("/StrF", "/Identity")
EFF = encryption_entry.get("/EFF", StmF)
if StmF != "/Identity":
StmF = filters[StmF]["/CFM"] # type: ignore
if StrF != "/Identity":
StrF = filters[StrF]["/CFM"] # type: ignore
if EFF != "/Identity":
EFF = filters[EFF]["/CFM"] # type: ignore
allowed_methods = ("/Identity", "/V2", "/AESV2", "/AESV3")
if StmF not in allowed_methods:
raise NotImplementedError("StmF Method {StmF} NOT supported!")
if StrF not in allowed_methods:
raise NotImplementedError(f"StrF Method {StrF} NOT supported!")
if EFF not in allowed_methods:
raise NotImplementedError(f"EFF Method {EFF} NOT supported!")
R = cast(int, encryption_entry["/R"])
return Encryption(V, R, encryption_entry, first_id_entry, StmF, StrF, EFF)