Cryptography and the Landauer Limit

Sunday, July 5, 2009

http://en.wikipedia.org/wiki/Landauer%27s_principle

In Hollywood, decrypting encrypted data is a simple matter of handing it off to a government lab or wunderkind and coming back in a few hours.

However, even if we were lenient toward Hollywood's fanciful views on computing power, there is another limitation which hackers are unlikely to get the better of: energy.

To bruteforce the decryption to AES-256 encrypted harddrive (commonly available for purchase) would require more energy than exists in the entire solar system. Even if you converted the sun and all the planets into pure energy, you would still come up short.

This is due to Landauer's principle. For a computational operation in which 1 bit of logical information is lost, the amount of entropy generated is at least k ln 2, and so the energy that must eventually be emitted to the environment is E ≥ kT ln 2. (k is the Boltzman constant and T is the temperature of the computer). For AES-256, 2^256 bits must be computed, which is quite a lot!

Possible remedy to this limitation may lie in the future development of reversible computing. If no information is erased, computation may be achieved which is thermodynamically reversible, and require no release of heat. The caveat is that this requires remembering previous states of the system, and must have available the memory necessary to do so.

35 comments

美岑 said...

感謝分享哦~會再來看看的~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

May 2, 2010 at 4:08 AM

加油!充實內函最重要!Beauty is but skin- deep..............................................

May 23, 2010 at 9:08 PM
芸茂 said...

Wise men learn by other mens mistakes; fools by their own. ............................................................

June 15, 2010 at 4:53 PM
許紀廷 said...
許紀廷 said...

人生最可憐的是半途而廢,最可悲的是喪失信心,最遺憾的是浪費時間,最可怕的是沒有恆心。..................................................

July 15, 2010 at 5:16 AM

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July 17, 2010 at 7:53 PM

不會從失敗中找尋教訓的人,成功之路是遙遠的。..................................................

July 20, 2010 at 5:48 AM
韋以韋以 said...

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July 22, 2010 at 10:24 PM

耐心是一株很苦的植物,但果實卻很甜美。..................................................

July 25, 2010 at 7:34 PM

一時的錯誤不算什麼,錯而不改才是一生中永遠且最大的錯誤..................................................

July 28, 2010 at 5:50 PM
怡于名君 said...

心中醒,口中說,紙上作,不從身上習過,皆無用也。.......................................................

August 3, 2010 at 10:24 PM
雅明修任 said...

在你一無所有的時候 是誰在陪伴你 他便是你最重要的人............................................................

August 6, 2010 at 12:33 PM
基韬 said...

Birthdays are good for you. The more you have, the longer you live...................................................................

August 9, 2010 at 3:27 AM
hui hui said...

聰明的人喜歡猜心 雖然每次都猜對了卻失去了自己的心............................................................

August 20, 2010 at 8:08 PM