Hash-based cryptography is the generic term for constructions of cryptographic primitives based on the security of hash functions. So far, hash-based cryptography is limited to digital signatures schemes such as the Merkle signature scheme. Hash-based signature schemes combine a one-time signature scheme with a Merkle tree structure. Since a one-time signature scheme key can only sign a single message securely, it is practical to combine many such keys within a single, larger structure. A Merkle tree structure is used to this end. In this hierarchical data structure, a hash function and concatenation are used repeatedly to compute tree nodes. Lamport signatures are an example of a one-time signature scheme that can be combined with a Merkle tree structure. Hash-based cryptography is a type of post-quantum cryptography.
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