ElGamal scheme may have some (not all) properties described On Sat, Nov 01, 2008 at 05:01:20PM -0700, yzt wrote: > > Hi, > > In my work, I need a cryptographic primitive (a cipher, to be more > specific) with the following attribute: > If we define the the encryption function as "E(k,p)" where "k" is the > key and "p" is the plain text, I need the cipher to have the property > that "E(k2, E(k1, p)) = E(k3, p)". In other words, I need the result > of the double encryption of any given plaintext with two different > keys, be equal to a single encryption with another key. > Obviously, I also need the "k3" above to be computable given "k1" and > "k2", but (ideally) neither "k1" nor "k2" should be retrievable given > the other two keys. > > Now, I don't have a strong theoretical background in cryptography, so > I don't even know what this property is called, or even whether it has > a specific name (that's why I had to choose such a non-descriptive > subject,) but as I understand it, this is generally an undesirable > property in a cipher. > Can such a property be implemented using conventional cryptographic > primitives? I would prefer the use of a block cipher, but public key- > based solutions wouldn't be too problematic either. Does anyone have > any advice as how should I go about implementing this? Does Crypto++ > have any features to help me here? > > I'm not even sure whether this mailing list is the proper place to ask > such questions. If so, I'd appreciate to be directed to the proper > place to ask this. I apologize if I'm violating any rules or > conventions. > > Any information, pointers, help or even RTFMs (with mention of the M > in point!) is greatly appreciated. I'd even appreciate it if someone > could tell me what this property is called, so I can do an informed > web search! > > -yzt >
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