I am trying to access big_map data for a specific key, but I found that I need to provide the hash of the key to retrieve the data. Is there a way to get the hash for a key? Knowing the algorithm used to generate the key should be good enough too.

2 Answers 2


Quick way (using Pytezos library):

>>> from pytezos.michelson.pack import get_key_hash
>>> get_key_hash({"string": "KT1PWx2mnDueood7fEmfbBDKx1D9BAnnXitn"}, {"prim": "address"})

Where first argument is the key (Micheline JSON), and the second one is the expression type (Micheline JSON).

Here is the algorithm and intermediate results (for value/type used above):

  1. Pack key (e.g. using pack_data RPC endpoint)
  2. Take Blake2b hash (digest size = 32)
  3. Prepend "0d2c401b"
  4. Base58 encode with checksum

I ended up using ConseilJS for this. I used the TezosMessageUtils.encodeBigMapKey function in ConseilJS to create the hash key. Here's an example of how to convert the key to the hash :

const packedKey = TezosMessageUtils.encodeBigMapKey(Buffer.from(TezosMessageUtils.writePackedData(secretHash, "bytes"), "hex"));

You need to put the appropriate type of your key in the writePackedData before encoding it.

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