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shared secret


Definition: shared secret: The idea that many people share the same password or key. Shared secrets are widely use because they are easy: there is simply one password to give out. On the other hand, the more widely secrets are shared, the more likely it will become compromised. In fact, many people believe that even sharing a secret among two people is extremely risky, where the proper solution is using public keys to distribute a randomly generated key only valid for the particular message. Example: DVD movies are encrypted with a randomly generated key. This key is then is then encrypted multiple times with hundreds of different keys. Every DVD player vendor owns one of these keys and imbeds it in their device, thus allows that player to decrypt the movie. (Presumably, if one of the keys is compromised, future movies can be generated without the offending key, causing players based upon that key to become obsolete). However, there is no good way to protect these keys, even though they are in hardware. In late 1999, students in Europe where able to break one of these keys (the Xing software DVD player), and from there they were able to break the majority of the other keys. (These keys only used 40-bit encryption, so breaking one key in the software player allowed a known-plaintext attack). From Hacking-Lexicon

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