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I'm reading “Identity-Based Broadcast Encryption with Constant Size Ciphertexts and Private Keys” by Cécile Delerablée.

On page 207, the encryption process needs $\gamma$ which is part of the master key. This does not make sense to me.

I want to know whether I read this thesis wrongly or not. Can anybody give me a opinion?

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That value can be computed with the data you have in the public key. You just need to use the fact: $$ h^{\gamma} \times h^{H(ID)} = h^{\gamma + H(ID)}. $$

Note that in the public key you have all the $h^{\gamma^i}$ you need for the computation.

The notation used in the paper is there to keep the notation easy and clear.

If you want to compute the correct value you could compute the product: $$\pi = \prod_{i=1}^s (\gamma + H(ID_i))$$ considering $\gamma$ as unknown and later compute $h^\pi$ making the needed substitutions.

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