CashAddr encoding

CashAddr encoding is an address format used in Bitcoin Cash. This is a Base32 encoding format that prevents confusion with Base58Check legacy address encoding also used by Bitcoin-BTC. The goal of the encoding is to make it easier to copy and to share information, by using a QR code for instance.

A Cash Address consists of:

• A prefix which is human-readable.
• A separator (:).
• A Base32 payload which contains a version byte and the data (or hash).
• A Base32 checksum.

This format reuses the work done for Bech32 (see BIP173) and is similar in some aspects, but improves on others. See the original specification for more details.

Prefix

The prefix is a human-readable part of the address which indicates the network on which the addess is valid, or the metaprotocol used. It can only contain ASCII characters.

There are 3 prefixes used in Bitcoin Cash to indicate the network:

The prefix can also indicate for which metaprotocol the addres must be used. For instance, Simple Ledger Protocol (SLP) addresses are required to begin with simpleledger in order to avoid sending SLP tokens to a non-SLP wallet.

The prefix is always followed by the separator :.

When presented to users, the prefix and the separator may be omitted as it is part of the checksum computation.

Base32

CashAddr uses Base32 to encode information. The symbols used in CashAddr Base32 are the lowercase alphanumeric characters excluding 1, b, i, and o. Uppercase characters are also valid to enable efficient QR code encoding (see spec). However, any mixture of lowercase and uppercase characters must be rejected.

Base32 alphabet:

qpzry9x8gf2tvdw0s3jn54khce6mua7l

Base32 symbol chart:

Version bytes

The version byte is divided into 3 parts:

• The most significant bit is reserved and must be 0.

• The 4 next bits indicate the type of address: 0b000 for P2PKH, and 0b001 for P2SH.

• The last 3 bits indicate the size of the data. This ensures that it is possible to check that the length of the address is correct. The size options are:

  Size bits	Data size (bytes)
  0b000	20
  0b001	24
  0b010	28
  0b011	32
  0b100	40
  0b101	48
  0b110	56
  0b111	64

For a legacy 20-byte (160-bit) hash, the follwoing version bytes are currently allowed:

Note that further types will be added as new features are added.

Checksum

The checksum is a 40 bits BCH code defined over the finite field GF(2^5). It ensures the detection of up to 6 errors in the address and 8 in a row. Combined with the length check, this provides very strong guarantee against errors.

The checksum is computed by the following polymod function (written in Python):

def polymod(values):
        c = 1
        for d in values:
            c0 = c >> 35
            c = ((c & 0x07ffffffff) << 5) ^ d
            if (c0 & 0x01):
                c ^= 0x98f2bc8e61
            if (c0 & 0x02):
                c ^= 0x79b76d99e2
            if (c0 & 0x04):
                c ^= 0xf33e5fb3c4
            if (c0 & 0x08):
                c ^= 0xae2eabe2a8
            if (c0 & 0x10):
                c ^= 0x1e4f43e470
        return c ^ 1

where & is the bitwise AND operator, ^ is the bitwise XOR operator, and >> is the bitwise right shift.

Encoding a Bitcoin Cash address

To encode an address with CashAddr, follow the steps described below:

1. Take the address data, which is usually the hash of a public key (P2PKH) or a redeem script (P2SH), and compute the corresponding version byte.

2. Concatenate the version byte and the data bytes together (bytewise):

   payload = version || data
   

3. Divide the payload into chunks of 5 bits. The payload is padded to the right with zero bits to complete any unfinished chunk at the end.

4. Compute the checksum by applying polymod to the following values:

   a. The lower 5 bits of each character of the prefix. For letters, this corresponds to their position in the alphabet.

   b. A zero for the separator (5 zero bits).

   c. The payload.

   d. Eight zeros as a template for the checksum.

5. Encode each chunk of the payload and each chunk of the checksum with Base32.

Example

The steps to encode a P2PKH address which is valid on the Bitcoin Cash main network are:

1. Take the address data, i.e., the 20-byte hash of the public key:

   211b74ca4686f81efda5641767fc84ef16dafe0b
   

2. Concatenate the version byte (here 0x00) and the data bytes together to get the payload:

   00211b74ca4686f81efda5641767fc84ef16dafe0b
   

3. Divide the payload into chunks of 5 bits. In this example, the payload is 168-bit long; therefore, it is padded to the right with 2 zero bits to complete the last chunk. The resulting chunks are:

   [ 0, 0, 16, 17, 22, 29, 6, 10, 8, 26, 3, 15, 16, 7, 23, 29, 20, 21, 18, 1, 14, 25, 31, 28, 16, 19, 23, 17, 13, 22, 23, 30, 1, 12 ]
   

4. Compute the checksum by applying polymod to the concatenation of:

   a. The lower 5 bits of each character of the prefix bitcoincash:

   [ 2, 9, 20, 3, 15, 9, 14, 3, 1, 19, 8 ]
   

   b. A zero for the separator:

   [ 0 ]
   

   c. The payload chunks:

   [ 0, 0, 16, 17, 22, 29, 6, 10, 8, 26, 3, 15, 16, 7, 23, 29, 20, 21, 18, 1, 14, 25, 31, 28, 16, 19, 23, 17, 13, 22, 23, 30, 1, 12 ]
   

   d. The template of the checksum:

   [ 0, 0, 0, 0, 0, 0, 0, 0 ]
   

   The checksum is:

   [ 28, 10, 17, 3, 2, 3, 3, 28 ]
   

5. Encoded with Base32, the payload and the checksum are, respectively, qqs3kax2g6r0s8ha54jpwelusnh3dkh7pv and u23rzrru. The resulting address is:

   bitcoincash:qqs3kax2g6r0s8ha54jpwelusnh3dkh7pvu23rzrru