CB58 is a format used to represent keys, addresses, and other binary values in web wallets and APIs. CB58 is the concatenation of the data bytes and a checksum. The checksum is created by taking the last four bytes of the SHA256 hash of the data bytes.
This concatenated output is then mapped to a base-58 string. It uses 58 lowercase letters, uppercase letters, and digits so values are easier to read and write. The alphabet for the base-58 conversion is:
Full implementation of the base-58 format can be found in AvalancheJS
CB58 is similar to Base58Check, but uses a different checksum algorithm.