# this is part of the einar project.
#
# Copyright ©  2024 - 2025 Juan Bindez  <juanbindez780@gmail.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.


import einar.exceptions as exception
import binascii

class AES:
    """Implementation of the AES (Advanced Encryption Standard) algorithm.
    
    This class provides AES-128 encryption and decryption functionality
    using ECB (Electronic Codebook) mode.

    """
    # Pre-calculated S-Box and Rcon tables for AES
    _s_box = (
        0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
        0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
        0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
        0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
        0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
        0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
        0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
        0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
        0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
        0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
        0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
        0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
        0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
        0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
        0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
        0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16,
    )

    _inv_s_box = (
        0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
        0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
        0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
        0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
        0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
        0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
        0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
        0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
        0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
        0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
        0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
        0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
        0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
        0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
        0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
        0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D,
    )

    _r_con = (
        0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40,
        0x80, 0x1B, 0x36, 0x6C, 0xD8, 0xAB, 0x4D, 0x9A,
        0x2F, 0x5E, 0xBC, 0x63, 0xC6, 0x97, 0x35, 0x6A,
        0xD4, 0xB3, 0x7D, 0xFA, 0xEF, 0xC5, 0x91, 0x39,
    )

    def __init__(self, key):
        """Initialize the AES cipher with a given key.
        
        Args:
            key (bytes): The encryption key (must be 16 bytes for AES-128)
            
        Raises:
            ValueError: If key length is not 16 bytes
        """

        if len(key) != 16:
            raise ValueError("AES-128 requires a 16-byte (128-bit) key")
        self._key = key
        self._expanded_key = self._expand_key(key)

    @classmethod
    def _sub_bytes(cls, s):
        """Substitute bytes in state matrix using AES S-Box."""
        for i in range(4):
            for j in range(4):
                s[i][j] = cls._s_box[s[i][j]]

    @classmethod
    def _inv_sub_bytes(cls, s):
        """Inverse substitute bytes in state matrix using inverse AES S-Box."""
        for i in range(4):
            for j in range(4):
                s[i][j] = cls._inv_s_box[s[i][j]]

    @staticmethod
    def _shift_rows(s):
        """Shift rows of the state matrix according to AES specification."""
        s[0][1], s[1][1], s[2][1], s[3][1] = s[1][1], s[2][1], s[3][1], s[0][1]
        s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
        s[0][3], s[1][3], s[2][3], s[3][3] = s[3][3], s[0][3], s[1][3], s[2][3]

    @staticmethod
    def _inv_shift_rows(s):
        """Inverse shift rows of the state matrix."""
        s[0][1], s[1][1], s[2][1], s[3][1] = s[3][1], s[0][1], s[1][1], s[2][1]
        s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
        s[0][3], s[1][3], s[2][3], s[3][3] = s[1][3], s[2][3], s[3][3], s[0][3]

    @staticmethod
    def _add_round_key(s, k):
        """Add (XOR) round key to the state matrix."""
        for i in range(4):
            for j in range(4):
                s[i][j] ^= k[i][j]

    @staticmethod
    def _xtime(a):
        """AES xtime operation (Galois Field multiplication by 2)."""
        return (((a << 1) ^ 0x1B) & 0xFF) if (a & 0x80) else (a << 1)

    @classmethod
    def _mix_single_column(cls, a):
        """Mix one column of the state matrix."""
        t = a[0] ^ a[1] ^ a[2] ^ a[3]
        u = a[0]
        a[0] ^= t ^ cls._xtime(a[0] ^ a[1])
        a[1] ^= t ^ cls._xtime(a[1] ^ a[2])
        a[2] ^= t ^ cls._xtime(a[2] ^ a[3])
        a[3] ^= t ^ cls._xtime(a[3] ^ u)

    @classmethod
    def _mix_columns(cls, s):
        """Mix all columns of the state matrix."""
        for i in range(4):
            cls._mix_single_column(s[i])

    @classmethod
    def _inv_mix_columns(cls, s):
        """Inverse mix all columns of the state matrix."""
        for i in range(4):
            u = cls._xtime(cls._xtime(s[i][0] ^ s[i][2]))
            v = cls._xtime(cls._xtime(s[i][1] ^ s[i][3]))
            s[i][0] ^= u
            s[i][1] ^= v
            s[i][2] ^= u
            s[i][3] ^= v
        cls._mix_columns(s)

    @staticmethod
    def _bytes2matrix(text):
        """Convert 16-byte array into 4x4 state matrix."""
        return [list(text[i:i+4]) for i in range(0, len(text), 4)]

    @staticmethod
    def _matrix2bytes(matrix):
        """Convert 4x4 state matrix into 16-byte array."""
        return bytes(sum(matrix, []))

    @staticmethod
    def _xor_bytes(a, b):
        """XOR two byte arrays together."""
        return bytes(i^j for i, j in zip(a, b))

    @staticmethod
    def _pad(plaintext):
        """Pad plaintext to be multiple of 16 bytes using PKCS#7 padding."""
        padding_len = 16 - (len(plaintext) % 16)
        padding = bytes([padding_len] * padding_len)
        return plaintext + padding

    @staticmethod
    def _unpad(plaintext):
        """Remove PKCS#7 padding from plaintext."""
        padding_len = plaintext[-1]
        assert padding_len > 0
        message, padding = plaintext[:-padding_len], plaintext[-padding_len:]
        assert all(p == padding_len for p in padding)
        return message

    @staticmethod
    def _split_blocks(message, block_size=16):
        """Split message into 16-byte blocks."""
        return [message[i:i+16] for i in range(0, len(message), 16)]

    @classmethod
    def _expand_key(cls, master_key):
        """Expand 16-byte master key into round keys."""
        key_columns = cls._bytes2matrix(master_key)
        iteration_size = len(master_key) // 4
        
        i = 1
        while len(key_columns) < (10 + 1) * 4:
            word = list(key_columns[-1])
            
            if len(key_columns) % iteration_size == 0:
                word.append(word.pop(0))
                word = [cls._s_box[b] for b in word]
                word[0] ^= cls._r_con[i]
                i += 1
            
            word = cls._xor_bytes(word, key_columns[-iteration_size])
            key_columns.append(word)
        
        return [key_columns[4*i : 4*(i+1)] for i in range(len(key_columns) // 4)]

    def _encrypt_block(self, plaintext):
        """Encrypt a single 16-byte block of plaintext."""
        plain_state = self._bytes2matrix(plaintext)
        
        self._add_round_key(plain_state, self._expanded_key[0])
        
        for i in range(1, 10):
            self._sub_bytes(plain_state)
            self._shift_rows(plain_state)
            self._mix_columns(plain_state)
            self._add_round_key(plain_state, self._expanded_key[i])
        
        self._sub_bytes(plain_state)
        self._shift_rows(plain_state)
        self._add_round_key(plain_state, self._expanded_key[-1])
        
        return self._matrix2bytes(plain_state)

    def _decrypt_block(self, ciphertext):
        """Decrypt a single 16-byte block of ciphertext."""
        cipher_state = self._bytes2matrix(ciphertext)
        
        self._add_round_key(cipher_state, self._expanded_key[-1])
        self._inv_shift_rows(cipher_state)
        self._inv_sub_bytes(cipher_state)
        
        for i in range(9, 0, -1):
            self._add_round_key(cipher_state, self._expanded_key[i])
            self._inv_mix_columns(cipher_state)
            self._inv_shift_rows(cipher_state)
            self._inv_sub_bytes(cipher_state)
        
        self._add_round_key(cipher_state, self._expanded_key[0])
        
        return self._matrix2bytes(cipher_state)

    def encrypt_ecb(self, plaintext):
        """Encrypt data in ECB (Electronic Codebook) mode.
        
        Args:
            plaintext (bytes): Data to encrypt
            
        Returns:
            bytes: Encrypted ciphertext
        """

        plaintext = self._pad(plaintext)
        blocks = []
        
        for plaintext_block in self._split_blocks(plaintext):
            block = self._encrypt_block(plaintext_block)
            blocks.append(block)
        
        return b''.join(blocks)

    def decrypt_ecb(self, ciphertext):
        """Decrypt data in ECB (Electronic Codebook) mode.
        
        Args:
            ciphertext (bytes): Data to decrypt
            
        Returns:
            bytes: Decrypted plaintext
        """

        blocks = []
        
        for ciphertext_block in self._split_blocks(ciphertext):
            block = self._decrypt_block(ciphertext_block)
            blocks.append(block)
        
        return self._unpad(b''.join(blocks))