AESXTS128

AESXTS128 is a variant of the XTS mode of operation for the Advanced Encryption Standard (AES) that uses two 128-bit keys. It is used in disk encryption to provide data confidentiality for stored data and to allow random access to encrypted storage.

In XTS, a tweak derived from the disk sector number and the block index is applied to each plaintext block. For each data block P_i in a sector, a tweak T_i is computed, often from the sector identifier. The block is then processed by XORing with T_i, encrypting with AES under the first key K1, and XORing with T_i again to produce the ciphertext C_i. Decryption uses the same process in reverse with the decryption function of AES under K1. The tweak ensures that identical plaintext blocks in different sectors or positions produce different ciphertext blocks, preventing pattern leakage.

Keying and data size: AESXTS128 uses two 128-bit keys, commonly denoted K1 and K2, for a total of 256 bits. It operates on 16-byte blocks and is designed to encrypt data organized into sectors, typically 512 or 4096 bytes in size.

Security and usage: XTS provides confidentiality but not integrity or authenticity. It is intended for storage devices and volume encryption where random access is needed. It is not a general-purpose authenticated encryption mode and should be paired with an independent integrity mechanism if data integrity is required. Correct implementation requires unique keys and proper tweak calculation; reusing tweaks or keys across volumes can compromise security.

Standards and adoption: XTS-AES is described in standards such as IEEE 1619 and NIST SP 800-38E. AESXTS128 is the 128-bit AES variant with two 128-bit keys that is widely supported by hardware and software libraries for disk encryption.