AES-256-CBC-CTS ENCRYPTION TOOL

Other Crypto Algorithms

AES-128-CBC AES-128-CBC-CTS AES-128-CBC-HMAC-SHA1 AES-128-CBC-HMAC-SHA256 AES-128-CCM AES-128-CFB AES-128-CFB1 AES-128-CFB8 AES-128-CTR AES-128-ECB AES-128-GCM AES-128-GCM-SIV AES-128-OCB AES-128-OFB AES-128-SIV AES-128-WRAP AES-128-WRAP-INV AES-128-WRAP-PAD AES-128-WRAP-PAD-INV AES-128-XTS AES-192-CBC AES-192-CBC-CTS AES-192-CCM AES-192-CFB AES-192-CFB1 AES-192-CFB8 AES-192-CTR AES-192-ECB AES-192-GCM AES-192-GCM-SIV AES-192-OCB AES-192-OFB AES-192-SIV AES-192-WRAP AES-192-WRAP-INV AES-192-WRAP-PAD AES-192-WRAP-PAD-INV AES-256-CBC AES-256-CBC-CTS AES-256-CBC-HMAC-SHA1 AES-256-CBC-HMAC-SHA256 AES-256-CCM AES-256-CFB AES-256-CFB1 AES-256-CFB8 AES-256-CTR AES-256-ECB AES-256-GCM AES-256-GCM-SIV AES-256-OCB AES-256-OFB AES-256-SIV AES-256-WRAP AES-256-WRAP-INV AES-256-WRAP-PAD AES-256-WRAP-PAD-INV AES-256-XTS ARIA-128-CBC ARIA-128-CCM ARIA-128-CFB ARIA-128-CFB1 ARIA-128-CFB8 ARIA-128-CTR ARIA-128-ECB ARIA-128-GCM ARIA-128-OFB ARIA-192-CBC ARIA-192-CCM ARIA-192-CFB ARIA-192-CFB1 ARIA-192-CFB8 ARIA-192-CTR ARIA-192-ECB ARIA-192-GCM ARIA-192-OFB ARIA-256-CBC ARIA-256-CCM ARIA-256-CFB ARIA-256-CFB1 ARIA-256-CFB8 ARIA-256-CTR ARIA-256-ECB ARIA-256-GCM ARIA-256-OFB CAMELLIA-128-CBC CAMELLIA-128-CBC-CTS CAMELLIA-128-CFB CAMELLIA-128-CFB1 CAMELLIA-128-CFB8 CAMELLIA-128-CTR CAMELLIA-128-ECB CAMELLIA-128-OFB CAMELLIA-192-CBC CAMELLIA-192-CBC-CTS CAMELLIA-192-CFB CAMELLIA-192-CFB1 CAMELLIA-192-CFB8 CAMELLIA-192-CTR CAMELLIA-192-ECB CAMELLIA-192-OFB CAMELLIA-256-CBC CAMELLIA-256-CBC-CTS CAMELLIA-256-CFB CAMELLIA-256-CFB1 CAMELLIA-256-CFB8 CAMELLIA-256-CTR CAMELLIA-256-ECB CAMELLIA-256-OFB CHACHA20 CHACHA20-POLY1305 DES-EDE-CBC DES-EDE-CFB DES-EDE-ECB DES-EDE-OFB DES-EDE3-CBC DES-EDE3-CFB DES-EDE3-CFB1 DES-EDE3-CFB8 DES-EDE3-ECB DES-EDE3-OFB DES3-WRAP

The AES-256-CBC-CTS algorithm is a symmetric key block cipher that combines the Advanced Encryption Standard (AES) with Cipher Block Chaining (CBC) mode and Ciphertext Stealing (CTS) for handling plaintexts that are not a multiple of the block size. AES operates on fixed-size blocks of 128 bits and supports key lengths of 128, 192, and 256 bits. In the AES-256 variant, a key of 256 bits is used to perform 14 rounds of transformations, including SubBytes, ShiftRows, MixColumns, and AddRoundKey operations. Each round transforms the data block using substitutions, permutations, and linear mixing to provide strong diffusion and confusion properties.

CBC Mode

CBC mode introduces dependency between sequential plaintext blocks by XORing each plaintext block with the previous ciphertext block before encryption. This chaining ensures that identical plaintext blocks produce different ciphertext blocks, enhancing security against pattern recognition attacks. An initialization vector (IV) is used for the first block to provide randomness. The IV must be unique for each encryption session and transmitted securely alongside the ciphertext.

Ciphertext Stealing (CTS)

CTS is applied when the plaintext length is not a multiple of the AES block size. Instead of padding the plaintext, CTS allows the last two ciphertext blocks to be adjusted so that the final block can contain fewer bytes while preserving the correct decryption. This technique ensures that the ciphertext length matches the plaintext length and avoids introducing additional padding artifacts.

Encryption Process

During encryption, the plaintext is divided into 128-bit blocks. Each block undergoes CBC processing: it is XORed with the previous ciphertext block or the IV for the first block, then encrypted using AES-256. If the final block is incomplete, CTS rearranges the last two blocks so that the ciphertext corresponds in length to the original plaintext. The output consists of a sequence of ciphertext blocks, including the IV if required.

Decryption Process

For decryption, the ciphertext is divided into blocks, and the last two blocks are adjusted according to CTS rules if needed. AES-256 decryption is applied in reverse, including the inverse round transformations. Each decrypted block is XORed with the previous ciphertext block or the IV to retrieve the original plaintext. CTS ensures that the plaintext is reconstructed accurately without requiring additional padding removal.

Security Considerations

AES-256-CBC-CTS provides strong confidentiality for data at rest and in transit. Proper management of the IV and the 256-bit key is critical. Reusing the IV or key compromises security. CBC mode combined with CTS allows secure handling of arbitrary-length data while maintaining the structural integrity of the plaintext length.

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