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Encoding scheme for API identifiers and byte arrays

The Aeternity node uses base58Check encoding for identifiers such as account and contract public keys. Base58c is not well suited for encoding big byte arrays, so for general byte arrays base64 is used.

The base64 encoded data is treated in the same way as the base58Check encoded data, i.e., a checksum is postfixed to the binary data before encoding. The checksum is the first four bytes of the sha256 hash of the sha256 hash of the original byte array.

The following erlang snippet shows how the checksum can be computed, and how it is added to the byte array that is to be encoded.

add_check_bytes(Bin) when is_binary(Bin) ->
  <<Check:4/binary, _/binary>> = sha256(sha256(Binary)),
  <<Bin/binary, Check/binary>>.

Both identifiers and general byte arrays are prefixed with a two letter tag and a separator (_), describing the type of data that is encoded. For example an account pubkey could look as ak_2a1j2Mk9YSmC1gioUq4PWRm3bsv887MbuRVwyv4KaUGoR1eiKi.

The tags are described below, together with the encoding method of the tag.

Prefix Encoding Description
ak base58 Account pubkey
bf base58 Block Proof of Fraud hash
bs base58 Block State hash
bx base58 Block transaction hash
cb base64 Contract byte array
ch base58 Channel
cm base58 Commitment
ct base58 Contract pubkey
kh base58 Key block hash
mh base58 Micro block hash
nm base58 Name
ok base58 Oracle pubkey
oq base58 Oracle query id
or base64 Oracle response
ov base64 Oracle query
pi base64 Proof of Inclusion
pp base58 Peer pubkey
sg base58 Signature
ss base64 State trees
cs base64 Contract calls state tree
ck base64 Contract state key
cv base64 Contract state value
st base64 State
th base58 Transaction hash
tx base64 Transaction