🔐 AES Full Encryption/Decryption Tool

AES (Advanced Encryption Standard) is a symmetric block cipher standardized by NIST. It operates on 128-bit blocks and uses key sizes of 128, 192, or 256 bits. AES is widely used for secure communications and data protection.

This tool allows you to visualize the complete AES encryption and decryption process, showing the state after each operation in every round.

AES encryption consists of the following steps:

1. Initial Round: AddRoundKey
2. Main Rounds (9, 11, or 13 rounds depending on key size):
   • SubBytes: Each byte is replaced using the S-box
   • ShiftRows: Rows are shifted cyclically
   • MixColumns: Columns are mixed using matrix multiplication in GF(2⁸)
   • AddRoundKey: XOR with the round key
3. Final Round:
   • SubBytes
   • ShiftRows
   • AddRoundKey (no MixColumns)

AES decryption performs the inverse operations in reverse order:

1. Initial Round: AddRoundKey
2. Main Rounds (9, 11, or 13 rounds depending on key size):
   • InvShiftRows: Rows are shifted cyclically in the opposite direction
   • InvSubBytes: Each byte is replaced using the inverse S-box
   • AddRoundKey: XOR with the round key
   • InvMixColumns: Columns are mixed using the inverse matrix multiplication in GF(2⁸)
3. Final Round:
   • InvShiftRows
   • InvSubBytes
   • AddRoundKey (no InvMixColumns)

The AES key expansion algorithm generates round keys from the cipher key. The number of round keys depends on the key size:

• AES-128: 11 round keys (10 rounds + initial)
• AES-192: 13 round keys (12 rounds + initial)
• AES-256: 15 round keys (14 rounds + initial)

The key expansion uses operations like RotWord (rotate word), SubWord (apply S-box), and XOR with round constants (RCON).