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The mode of operation used by VeraCrypt for encrypted partitions, drives, and virtual volumes is XTS.

XTS mode is in fact XEX mode [12], which was designed by Phillip Rogaway in 2003, with a minor modification (XEX mode uses a single key for two different purposes, whereas XTS mode uses two independent keys).

In 2010, XTS mode was approved by NIST for protecting the confidentiality of data on storage devices [24]. In 2007, it was also approved by the IEEE for cryptographic protection of data on block-oriented storage devices (IEEE 1619).

Where:

^{ } |
denotes multiplication of two polynomials over the binary field GF(2) modulo
x^{128}+x^{7}+x^{2}+x+1 |

K1 |
is the encryption key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish) |

K2 |
is the secondary key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish) |

i |
is the cipher block index within a data unit; for the first cipher block within a data unit, i = 0 |

n |
is the data unit index within the scope of K1; for the first data unit,
n = 0 |

a |
is a primitive element of Galois Field (2 ^{128}) that corresponds to polynomial
x (i.e., 2) |

Note: The remaining symbols are defined in the section Notation. |

The size of each data unit is always 512 bytes (regardless of the sector size).