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TrueCrypt supports encrypting a system partition while operating system is running.

From the docs:

Note that TrueCrypt can encrypt an existing unencrypted system partition/drive in-place while the operating system is running (while the system is being encrypted, you can use your computer as usual without any restrictions). Likewise, a TrueCrypt-encrypted system partition/drive can be decrypted in-place while the operating system is running. You can interrupt the process of encryption or decryption anytime, leave the partition/drive partially unencrypted, restart or shut down the computer, and then resume the process, which will continue from the point it was stopped.

The question is. How is it implemented? How does TrueCrypt keep one part of the partition encrypted and the other non-encrypted? And how does it provide access to both parts while constantly encrypting the unencrypted one? What happens if the systems tries to access the data (or even write it) which is being encrypted at the moment (transferred from non-encrypted section of the partition into encrypted)?

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This question isn't really related to cryptography, so unfortunately it's off-topic here. – CodesInChaos Oct 12 '12 at 11:50
2  
Live encryption doesn't sound that hard. You just need to keep track of which part of the harddisk you already encryption. The pass operations on these hard-disk parts though the encryption/decryption function, and have the operations on other parts of the disk bypass the encryption. – CodesInChaos Oct 12 '12 at 11:51
Yup - as far as I can remember from a talk on this, that is exactly what is done. Along with some extra journalling etc to avoid problems in case of halting mid job and so on. – Rory Alsop Oct 12 '12 at 13:07

closed as off topic by CodesInChaos, Antony Vennard, mikeazo♦ Oct 12 '12 at 13:29

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