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There is a related question, but the differences are still not clear. These five types are mentioned in the Michelson whitedoc with the following definitions:

  • address: An untyped address (implicit account or smart contract).
  • contract 'param: A contract, with the type of its code, contract unit for implicit accounts.
  • key: A public cryptographic key.
  • key_hash: The hash of a public cryptographic key.
  • signature: A cryptographic signature.

    1. What is the difference between key_hash and address? It seems like for both I can do PUSH address "tz1..." and PUSH key_hash "tz1..." using the same string literal. I remember seeing something about reveal. What does reveal mean?

    2. Why can I convert between address and contract. But not between address and key_hash?

    3. What is the difference between key and key_hash? When would I have a key, but not a key_hash?

    4. What is a cryptographic signature and what are some of the use cases in Michelson?

    5. Any other important details about these data types.

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  1. key_hash is blake2b hash of a public key, in the base58 encoded form it can start only with tz, but address is more general, it can also hold KT accounts;
  2. There are no instructions for that, probably because it's a rare and arguable case; EDIT: as pointed out by Raphaël, you can convert key_hash to contract and then to address using IMPLICIT_ACCOUNT ; ADDRESS
  3. As was mentioned, key_hash is blake2b hash of key. You would need a key for checking a signature for instance;
  4. Allow me to link wikipedia https://ru.wikipedia.org/wiki/EdDSA. A bright example is a multisig contract;
  5. Check out the new Michelson documentation https://michelson.nomadic-labs.com/

To sum up:

  • key represents a public key (a point on the elliptic curve)
  • key_hash is blake2b hash of key
  • address is a general representation of Tezos accounts, including both - tz and KT addresses
  • signature is a result of signing a message with a private key using the elliptic curve digital signature scheme.
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Why can I convert between address and contract. But not between address and key_hash?

There is the (IMPLICIT_ACCOUNT) instruction to go from key_hash to address. For the other direction, there was (a feature request) but it was closed because no use case has been presented to motivate it.

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