BUIP045: Unified addresses format for BUIP037
Proposer: Amaury SÉCHET
Submitted: 2017-01-12
Status: draft

This is mostly an adaptation of Rusty Russel’s
work for
BUIP037.

The address is composed of the following elements:

1. Prefix for type, followed by colon. Currently “btc:” or “testnet:”.
2. The version field, encoded using
   z-base32
3. The hash field, encoded using
   z-base32
4. At least 35 bits for crc64-ecma, up to a multiple of 5 to reach a
   letter boundary. This covers the prefix (as ascii), the version and the
   hash.
5. The final letter is the Damm
   algorithm check digit of
   the entire previous string, using the 32 way quasigroup formed by
   GF(2^5) and x^5 + x^2 + 1 as base polynomial and n = 2*x + y as
   generator.

Step 4 and 5 add 8 characters to the address, 7 for CRC and 1 for Damm,
and ensure this

This has various advantages:

• A unified address format for all current addresses and futures
  features to come.
• Nicer looking than base58 - subjective but base58 addresses tends to
  be intimidating for newcomers.
• Protected against errors via a CRC64.
• Protected against any single character change via Damm.
• As long as the number of version is kept under 64, the first letter
  indicate the type of address as it is the 5 most significant digit of
  the version.
• Addresses are compact enough, 42 digit for 20B hash, 61 for 32B.

Example (I did not run CRC or Damm on them, just filled with random
digits):
btc:yybul3unspd4bn2aji33natie5sd2iqsikrfgm8ejk (42 digits for a P2KH,
20B hash).
btc:b1ee6ceodhmo2d0rmr7utt31u0163kdoakirgoigsd112d5batlt2a (61 digits
for a P2SH, 32B hash).