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What exactly is the purpose of the multi-tree variant in hash-based signature schemes? The biggest reason for using a multitree variant is to keep the public key generation time reasonable, even if the upper limit on the number of signatures is huge. With a single Merkle tree, the value of the root is a function of all the Winternitz public keys. That is, ...


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Apparently one can make the signature much shorter, by hashing the above again. Boneh and Shoup define Winternitz signatures in this way No, Bohen and Shoup do not; their Winternitz signature is a concatination of the hashes. This can be seen as the output of their $S(sk, m)$ algorithm on page 591 of version 0.5 of their book - the signature they generate ...


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Is the Lamport-Diffie signature secure in the standard model? Technically, no, the Lamport(-Diffie) one-time signature scheme is not EUF-CMA secure, however, also technically "it depends". Nominally, a signature scheme is typically called "secure" - especially in the public-key world - if for a polynomial number of adverserial ...


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