co-Computational Diffie-Hellman

The CDH problem across the two groups of an asymmetric bilinear pairing: given $g_2,g_2^a\in {\mathbb{G}}_2$ and $h\in {\mathbb{G}}_1$, compute $h^a$; it is the assumption under which BLS signatures are EUF-CMA secure in the random oracle model.

TODO: syntax and security definition.

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Builds on co-Computational Diffie-Hellman

• co-CDH ⇒ DS