pypdf/_crypt_providers/_fallback.py

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from pypdf._crypt_providers._base import CryptBase
from pypdf.errors import DependencyError

_DEPENDENCY_ERROR_STR = "cryptography>=3.1 is required for AES algorithm"


crypt_provider = ("local_crypt_fallback", "0.0.0")


class CryptRC4(CryptBase):
    def __init__(self, key: bytes) -> None:
        self.s = bytearray(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 = bytearray(self.s)
        out = [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(out)

    def decrypt(self, data: bytes) -> bytes:
        return self.encrypt(data)


class CryptAES(CryptBase):
    def __init__(self, key: bytes) -> None:
        pass

    def encrypt(self, data: bytes) -> bytes:
        raise DependencyError(_DEPENDENCY_ERROR_STR)

    def decrypt(self, data: bytes) -> bytes:
        raise DependencyError(_DEPENDENCY_ERROR_STR)


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(_DEPENDENCY_ERROR_STR)


def aes_ecb_decrypt(key: bytes, data: bytes) -> bytes:
    raise DependencyError(_DEPENDENCY_ERROR_STR)


def aes_cbc_encrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
    raise DependencyError(_DEPENDENCY_ERROR_STR)


def aes_cbc_decrypt(key: bytes, iv: bytes, data: bytes) -> bytes:
    raise DependencyError(_DEPENDENCY_ERROR_STR)