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< title > VeraCrypt - Free Open source disk encryption with strong security for the Paranoid< / title >
< meta name = "description" content = "VeraCrypt is free open-source disk encryption software for Windows, Mac OS X and Linux. In case an attacker forces you to reveal the password, VeraCrypt provides plausible deniability. In contrast to file encryption, data encryption performed by VeraCrypt is real-time (on-the-fly), automatic, transparent, needs very little memory, and does not involve temporary unencrypted files." / >
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< a href = "Documentation.html" > Documentation< / a >
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< a href = "Technical%20Details.html" > Technical Details< / a >
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< a href = "Modes%20of%20Operation.html" > Modes of Operation< / a >
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< h1 > Modes of Operation< / h1 >
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The mode of operation used by VeraCrypt for encrypted partitions, drives, and virtual volumes is XTS.
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XTS mode is in fact XEX mode < a href = "http://www.cs.ucdavis.edu/%7Erogaway/papers/offsets.pdf" >
[12]< / a > , 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).< br style = "text-align:left" >
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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).< / div >
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< strong style = "text-align:left" > Description of XTS mode< / strong > :< / h2 >
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< em style = "text-align:left" > C< sub style = "text-align:left; font-size:85%" > i< / sub > < / em > =
< em style = "text-align:left" > E< / em > < sub style = "text-align:left; font-size:85%" > < em style = "text-align:left" > K< / em > 1< / sub > (< em style = "text-align:left" > P< sub style = "text-align:left; font-size:85%" > i< / sub > < / em > ^ (< em style = "text-align:left" > E< / em > < sub style = "text-align:left; font-size:85%" > < em style = "text-align:left" > K< / em > 2< / sub > (< em style = "text-align:left" > n< / em > )
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< em style = "text-align:left" > a< sup style = "text-align:left; font-size:85%" > i< / sup > < / em > )) ^ (< em style = "text-align:left" > E< / em > < sub style = "text-align:left; font-size:85%" > < em style = "text-align:left" > K< / em > 2< / sub > (< em style = "text-align:left" > n< / em > )
< img src = "gf2_mul.gif" alt = "" width = "10" height = "10" > < em style = "text-align:left" > a< sup style = "text-align:left; font-size:85%" > i< / sup > < / em > )< / div >
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Where:< / div >
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< sup style = "text-align:left; font-size:85%" > < img src = "gf2_mul.gif" alt = "" width = "10" height = "10" > < / sup > < / td >
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denotes multiplication of two polynomials over the binary field GF(2) modulo < em style = "text-align:left" >
x< / em > < sup style = "text-align:left; font-size:85%" > 128< / sup > + < em style = "text-align:left" > x< / em > < sup style = "text-align:left; font-size:85%" > 7< / sup > + < em style = "text-align:left" > x< / em > < sup style = "text-align:left; font-size:85%" > 2< / sup > + < em style = "text-align:left" > x< / em > + 1< / td >
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< em style = "text-align:left" > K< / em > 1< / td >
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is the encryption key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish)< / td >
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< em style = "text-align:left" > K< / em > 2< / td >
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is the secondary key (256-bit for each supported cipher; i.e, AES, Serpent, and Twofish)< / td >
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< em style = "text-align:left" > i< / em > < / td >
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is the cipher block index within a data unit; for the first cipher block within a data unit,
< em style = "text-align:left" > i< / em > = 0< / td >
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< em style = "text-align:left" > n< / em > < / td >
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is the data unit index within the scope of < em style = "text-align:left" > K< / em > 1; for the first data unit,
< em style = "text-align:left" > n< / em > = 0< / td >
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< em style = "text-align:left" > a< / em > < / td >
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is a primitive element of Galois Field (2< sup style = "text-align:left; font-size:85%" > 128< / sup > ) that corresponds to polynomial
< em style = "text-align:left" > x< / em > (i.e., 2)< / td >
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< span style = "text-align:left; font-size:10px; line-height:12px" > Note: The remaining symbols are defined in the section
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Notation< / a > . < / span > < / td >
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The size of each data unit is always 512 bytes (regardless of the sector size).< / div >
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For further information pertaining to XTS mode, see e.g. < a href = "http://www.cs.ucdavis.edu/%7Erogaway/papers/offsets.pdf" style = "text-align:left; color:#0080c0; text-decoration:none" >
[12]< / a > and < a href = "http://csrc.nist.gov/publications/nistpubs/800-38E/nist-sp-800-38E.pdf" style = "text-align:left; color:#0080c0; text-decoration:none" >
[24]< / a > .< / div >
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