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Bitcoin Cash (BCH)

Жаңартылды

Abstract

This document describes a proposed address format to be used on Bitcoin Cash. It is a base32 encoded format using BCH[1] codes as checksum and that can be used directly in links or QR codes.

This format reuses the work done for Bech32[2] and is similar in some aspects, but improves on others.

Specification

The address is composed of

  1. A prefix indicating the network on which this address is valid.
  2. A separator, always :
  3. A base32 encoded payload indicating the destination of the address and containing a checksum.

Prefix

The prefix indicates the network on which this addess is valid. It is set to bitcoincash for Bitcoin Cash main net, bchtest for bitcoin cash testnet and bchreg for bitcoin cash regtest.

The prefix is followed by the separator :.

When presented to users, the prefix may be omitted as it is part of the checksum computation. The checksum ensures that addresses on different networks will remain incompatible, even in the absence of an explicit prefix.

Payload

The payload is a base32 encoded stream of data.

  0 1 2 3 4 5 6 7
+0 q p z r y 9 x 8
+8 g f 2 t v d w 0
+16 s 3 j n 5 4 k h
+24 c e 6 m u a 7 l

The payload is composed of 3 elements:

  1. A version byte indicating the type of address.
  2. A hash.
  3. A 40 bits checksum.

Version byte

The version byte's most signficant bit is reserved and must be 0. The 4 next bits indicate the type of address and the 3 least significant bits indicate the size of the hash.

Size bits Hash size in bits
0 160
1 192
2 224
3 256
4 320
5 384
6 448
7 512

Encoding the size of the hash in the version field ensure that it is possible to check that the length of the address is correct.

Type bits Meaning Version byte value
0 P2KH 0
1 P2SH 8

Further types will be added as new features are added.

Hash

The hash part really deserves not much explanation as its meaning is dependent on the version field. It is the hash that represents the data, namely a hash of the public key for P2KH and the hash of the reedemScript for P2SH.

Checksum

The checksum is a 40 bits BCH codes defined over 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 per the code below:


  uint64_t PolyMod(const data &v) {
    uint64_t c = 1;
    for (uint8_t d : v) {
      uint8_t 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;
  }

The checksum is calculated over the following data (list of integers in range 0-31):

  1. The lower 5 bits of each character of the prefix. - e.g. "bit..." becomes 2,9,20,...
  2. A zero for the separator (5 zero bits).
  3. The payload by chunks of 5 bits. If necessary, the payload is padded to the right with zero bits to complete any unfinished chunk at the end.
  4. Eight zeros as a "template" for the checksum.

The 40-bit number returned by PolyMod is split into eight 5-bit numbers (msb first). The payload and the checksum are then encoded according to the base32 character table.

To verify a base32-formatted address, it is split at the colon ":" into prefix and payload. Input data (list of integers) for PolyMod function is assembled from these parts:

  1. The lower 5 bits of each characters of the prefix.
  2. A zero for the separator (5 zero bits).
  3. Each base32 char of the payload mapped to it's respective number. If PolyMod returns non-zero, then the address was broken.

The following adresses can be used as test vector for checksum computation:

  • prefix:x64nx6hz
  • p:gpf8m4h7
  • bitcoincash:qpzry9x8gf2tvdw0s3jn54khce6mua7lcw20ayyn
  • bchtest:testnetaddress4d6njnut
  • bchreg:555555555555555555555555555555555555555555555udxmlmrz

NB: These addresses do not have valid payload on purpose.

Error correction

BCH codes allows for error correction. However, it is strongly advised that error correction is not done in an automatic manner as it may cause funds to be lost irrecoverably if done incorrectly. It may however be used to hint a user at a possible error.

Uppercase/lowercase

Lower case is preferred for cashaddr, but uppercase is accepted. A mixture of lower case and uppercase must be rejected.

Allowing for uppercase ensures that the address can be encoded efficiently in QR codes using the alphanumeric mode[3].

Double prefix

In some contexts, such as payment URLs or QR codes, the addresses are currently prefixed with bitcoincash:. In these contexts, the address must not be double prefixed.

Examples of address translation

The following addresses are given in the legacy and new format.

Legacy CashAddr
1BpEi6DfDAUFd7GtittLSdBeYJvcoaVggu bitcoincash:qpm2qsznhks23z7629mms6s4cwef74vcwvy22gdx6a
1KXrWXciRDZUpQwQmuM1DbwsKDLYAYsVLR bitcoincash:qr95sy3j9xwd2ap32xkykttr4cvcu7as4y0qverfuy
16w1D5WRVKJuZUsSRzdLp9w3YGcgoxDXb bitcoincash:qqq3728yw0y47sqn6l2na30mcw6zm78dzqre909m2r
3CWFddi6m4ndiGyKqzYvsFYagqDLPVMTzC bitcoincash:ppm2qsznhks23z7629mms6s4cwef74vcwvn0h829pq
3LDsS579y7sruadqu11beEJoTjdFiFCdX4 bitcoincash:pr95sy3j9xwd2ap32xkykttr4cvcu7as4yc93ky28e
31nwvkZwyPdgzjBJZXfDmSWsC4ZLKpYyUw bitcoincash:pqq3728yw0y47sqn6l2na30mcw6zm78dzq5ucqzc37

Larger Test Vectors

This table defines test vectors for various payloads of sizes 160-512 bits with various prefixes. These test vectors aren't given in legacy address format because the legacy format is limited to payloads of 160 bits.

Payload Size (bytes) Type CashAddr Payload (hex)
20 0 bitcoincash:qr6m7j9njldwwzlg9v7v53unlr4jkmx6eylep8ekg2 F5BF48B397DAE70BE82B3CCA4793F8EB2B6CDAC9
20 1 bchtest:pr6m7j9njldwwzlg9v7v53unlr4jkmx6eyvwc0uz5t F5BF48B397DAE70BE82B3CCA4793F8EB2B6CDAC9
20 1 pref:pr6m7j9njldwwzlg9v7v53unlr4jkmx6ey65nvtks5 F5BF48B397DAE70BE82B3CCA4793F8EB2B6CDAC9
20 15 prefix:0r6m7j9njldwwzlg9v7v53unlr4jkmx6ey3qnjwsrf F5BF48B397DAE70BE82B3CCA4793F8EB2B6CDAC9
24 0 bitcoincash:q9adhakpwzztepkpwp5z0dq62m6u5v5xtyj7j3h2ws4mr9g0 7ADBF6C17084BC86C1706827B41A56F5CA32865925E946EA
24 1 bchtest:p9adhakpwzztepkpwp5z0dq62m6u5v5xtyj7j3h2u94tsynr 7ADBF6C17084BC86C1706827B41A56F5CA32865925E946EA
24 1 pref:p9adhakpwzztepkpwp5z0dq62m6u5v5xtyj7j3h2khlwwk5v 7ADBF6C17084BC86C1706827B41A56F5CA32865925E946EA
24 15 prefix:09adhakpwzztepkpwp5z0dq62m6u5v5xtyj7j3h2p29kc2lp 7ADBF6C17084BC86C1706827B41A56F5CA32865925E946EA
28 0 bitcoincash:qgagf7w02x4wnz3mkwnchut2vxphjzccwxgjvvjmlsxqwkcw59jxxuz 3A84F9CF51AAE98A3BB3A78BF16A6183790B18719126325BFC0C075B
28 1 bchtest:pgagf7w02x4wnz3mkwnchut2vxphjzccwxgjvvjmlsxqwkcvs7md7wt 3A84F9CF51AAE98A3BB3A78BF16A6183790B18719126325BFC0C075B
28 1 pref:pgagf7w02x4wnz3mkwnchut2vxphjzccwxgjvvjmlsxqwkcrsr6gzkn 3A84F9CF51AAE98A3BB3A78BF16A6183790B18719126325BFC0C075B
28 15 prefix:0gagf7w02x4wnz3mkwnchut2vxphjzccwxgjvvjmlsxqwkc5djw8s9g 3A84F9CF51AAE98A3BB3A78BF16A6183790B18719126325BFC0C075B
32 0 bitcoincash:qvch8mmxy0rtfrlarg7ucrxxfzds5pamg73h7370aa87d80gyhqxq5nlegake 3173EF6623C6B48FFD1A3DCC0CC6489B0A07BB47A37F47CFEF4FE69DE825C060
32 1 bchtest:pvch8mmxy0rtfrlarg7ucrxxfzds5pamg73h7370aa87d80gyhqxq7fqng6m6 3173EF6623C6B48FFD1A3DCC0CC6489B0A07BB47A37F47CFEF4FE69DE825C060
32 1 pref:pvch8mmxy0rtfrlarg7ucrxxfzds5pamg73h7370aa87d80gyhqxq4k9m7qf9 3173EF6623C6B48FFD1A3DCC0CC6489B0A07BB47A37F47CFEF4FE69DE825C060
32 15 prefix:0vch8mmxy0rtfrlarg7ucrxxfzds5pamg73h7370aa87d80gyhqxqsh6jgp6w 3173EF6623C6B48FFD1A3DCC0CC6489B0A07BB47A37F47CFEF4FE69DE825C060
40 0 bitcoincash:qnq8zwpj8cq05n7pytfmskuk9r4gzzel8qtsvwz79zdskftrzxtar994cgutavfklv39gr3uvz C07138323E00FA4FC122D3B85B9628EA810B3F381706385E289B0B25631197D194B5C238BEB136FB
40 1 bchtest:pnq8zwpj8cq05n7pytfmskuk9r4gzzel8qtsvwz79zdskftrzxtar994cgutavfklvmgm6ynej C07138323E00FA4FC122D3B85B9628EA810B3F381706385E289B0B25631197D194B5C238BEB136FB
40 1 pref:pnq8zwpj8cq05n7pytfmskuk9r4gzzel8qtsvwz79zdskftrzxtar994cgutavfklv0vx5z0w3 C07138323E00FA4FC122D3B85B9628EA810B3F381706385E289B0B25631197D194B5C238BEB136FB
40 15 prefix:0nq8zwpj8cq05n7pytfmskuk9r4gzzel8qtsvwz79zdskftrzxtar994cgutavfklvwsvctzqy C07138323E00FA4FC122D3B85B9628EA810B3F381706385E289B0B25631197D194B5C238BEB136FB
48 0 bitcoincash:qh3krj5607v3qlqh5c3wq3lrw3wnuxw0sp8dv0zugrrt5a3kj6ucysfz8kxwv2k53krr7n933jfsunqex2w82sl E361CA9A7F99107C17A622E047E3745D3E19CF804ED63C5C40C6BA763696B98241223D8CE62AD48D863F4CB18C930E4C
48 1 bchtest:ph3krj5607v3qlqh5c3wq3lrw3wnuxw0sp8dv0zugrrt5a3kj6ucysfz8kxwv2k53krr7n933jfsunqnzf7mt6x E361CA9A7F99107C17A622E047E3745D3E19CF804ED63C5C40C6BA763696B98241223D8CE62AD48D863F4CB18C930E4C
48 1 pref:ph3krj5607v3qlqh5c3wq3lrw3wnuxw0sp8dv0zugrrt5a3kj6ucysfz8kxwv2k53krr7n933jfsunqjntdfcwg E361CA9A7F99107C17A622E047E3745D3E19CF804ED63C5C40C6BA763696B98241223D8CE62AD48D863F4CB18C930E4C
48 15 prefix:0h3krj5607v3qlqh5c3wq3lrw3wnuxw0sp8dv0zugrrt5a3kj6ucysfz8kxwv2k53krr7n933jfsunqakcssnmn E361CA9A7F99107C17A622E047E3745D3E19CF804ED63C5C40C6BA763696B98241223D8CE62AD48D863F4CB18C930E4C
56 0 bitcoincash:qmvl5lzvdm6km38lgga64ek5jhdl7e3aqd9895wu04fvhlnare5937w4ywkq57juxsrhvw8ym5d8qx7sz7zz0zvcypqscw8jd03f D9FA7C4C6EF56DC4FF423BAAE6D495DBFF663D034A72D1DC7D52CBFE7D1E6858F9D523AC0A7A5C34077638E4DD1A701BD017842789982041
56 1 bchtest:pmvl5lzvdm6km38lgga64ek5jhdl7e3aqd9895wu04fvhlnare5937w4ywkq57juxsrhvw8ym5d8qx7sz7zz0zvcypqs6kgdsg2g D9FA7C4C6EF56DC4FF423BAAE6D495DBFF663D034A72D1DC7D52CBFE7D1E6858F9D523AC0A7A5C34077638E4DD1A701BD017842789982041
56 1 pref:pmvl5lzvdm6km38lgga64ek5jhdl7e3aqd9895wu04fvhlnare5937w4ywkq57juxsrhvw8ym5d8qx7sz7zz0zvcypqsammyqffl D9FA7C4C6EF56DC4FF423BAAE6D495DBFF663D034A72D1DC7D52CBFE7D1E6858F9D523AC0A7A5C34077638E4DD1A701BD017842789982041
56 15 prefix:0mvl5lzvdm6km38lgga64ek5jhdl7e3aqd9895wu04fvhlnare5937w4ywkq57juxsrhvw8ym5d8qx7sz7zz0zvcypqsgjrqpnw8 D9FA7C4C6EF56DC4FF423BAAE6D495DBFF663D034A72D1DC7D52CBFE7D1E6858F9D523AC0A7A5C34077638E4DD1A701BD017842789982041
64 0 bitcoincash:qlg0x333p4238k0qrc5ej7rzfw5g8e4a4r6vvzyrcy8j3s5k0en7calvclhw46hudk5flttj6ydvjc0pv3nchp52amk97tqa5zygg96mtky5sv5w D0F346310D5513D9E01E299978624BA883E6BDA8F4C60883C10F28C2967E67EC77ECC7EEEAEAFC6DA89FAD72D11AC961E164678B868AEEEC5F2C1DA08884175B
64 1 bchtest:plg0x333p4238k0qrc5ej7rzfw5g8e4a4r6vvzyrcy8j3s5k0en7calvclhw46hudk5flttj6ydvjc0pv3nchp52amk97tqa5zygg96mc773cwez D0F346310D5513D9E01E299978624BA883E6BDA8F4C60883C10F28C2967E67EC77ECC7EEEAEAFC6DA89FAD72D11AC961E164678B868AEEEC5F2C1DA08884175B
64 1 pref:plg0x333p4238k0qrc5ej7rzfw5g8e4a4r6vvzyrcy8j3s5k0en7calvclhw46hudk5flttj6ydvjc0pv3nchp52amk97tqa5zygg96mg7pj3lh8 D0F346310D5513D9E01E299978624BA883E6BDA8F4C60883C10F28C2967E67EC77ECC7EEEAEAFC6DA89FAD72D11AC961E164678B868AEEEC5F2C1DA08884175B
64 15 prefix:0lg0x333p4238k0qrc5ej7rzfw5g8e4a4r6vvzyrcy8j3s5k0en7calvclhw46hudk5flttj6ydvjc0pv3nchp52amk97tqa5zygg96ms92w6845 D0F346310D5513D9E01E299978624BA883E6BDA8F4C60883C10F28C2967E67EC77ECC7EEEAEAFC6DA89FAD72D11AC961E164678B868AEEEC5F2C1DA08884175B

References

[1] https://en.wikipedia.org/wiki/BCH_code

[2] https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki

[3] http://www.thonky.com/qr-code-tutorial/alphanumeric-mode-encoding

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