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hacker · 10-01-2004, 11:22 AM

If you have a one-way hash, it absolutely cannot be used as a "decryption key" in any way, period. That is why it is called one-way. It cannot be turned around, or reversed, decrypted, or decoded to get the original key back out.

The hash itself, is stored (of course), and any entered "registration" value is hashed using the same method as the first hash, and compared to the stored value. If the two values match, the registration is assumed to be the same as the one that was used to "register" the book in the first place. If they do not match, then it is assumed to be different.

You cannot use a one-way hash as a key to decrypt anything. Hashes are encoded, not encrypted. They cannot be "reversed" back into anything. See this informative page for more details with great flowcharts and diagrams. There is also a nice write up on SHA-0 and SHA-1 on Wikipedia.

It is computationally infeasible to find any original data with that hash; in fact you can't determine any usable information about the original data with that hash, not even a single bit. For some one-way hash functions it's also computationally impossible to determine two different pieces of data which produce the same hash.

10-01-2004, 11:22 AM	#2
hacker Technology Mercenary Posts: 617 Karma: 2561 Join Date: Feb 2003 Location: East Lyme, CT Device: Direct Neural Implant	If you have a one-way hash, it *absolutely cannot be* used as a "decryption key" in any way, period. That is why it is called one-way. It cannot be turned around, or reversed, decrypted, or decoded to get the original key back out. The hash itself, is stored (of course), and any entered "registration" value is hashed using the same method as the first hash, and compared to the stored value. If the two values match, the registration is assumed to be the same as the one that was used to "register" the book in the first place. If they do not match, then it is assumed to be different. You *cannot* use a one-way hash as a key to decrypt anything. Hashes are encoded, not encrypted. They cannot be "reversed" back into anything. See this informative page for more details with great flowcharts and diagrams. There is also a nice write up on SHA-0 and SHA-1 on Wikipedia. It is computationally infeasible to find any original data with that hash; in fact you can't determine any usable information about the original data with that hash, *not even a single bit*. For some one-way hash functions it's also computationally impossible to determine two different pieces of data which produce the same hash.