Step by step guide to go from public key to a Bech32 encoded address

larry_vw_1955

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Quote from: pooya87 on October 29, 2021, 01:00:43 AM

It does. Bech32 encoding was introduced to let users use the new SegWit outputs that is was a "leap forward in technology".

a leap forward in error checking maybe but just saying that if you use this address type then we won't make you pay as many fees doesn't mean any great technological achievement. it's kind of arbitrary. Grin

thanks for the comment about bip38 but i'm not willing to accept a modification to it that would use any of the flagbyte that they have reserved for future possible uses.

pooya87

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Quote from: larry_vw_1955 on October 29, 2021, 12:33:19 AM

I don't really see the benefit of new address types that represent the same old public key.

Addresses have never represented public keys, they always represent a script. When a new address is introduced that means a new standard script was introduced (P2PKH > P2SH > P2WPKH/P2WSH > P2TR).

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they incentived using bech32 but that doesn't mean really that its better. or represents any kind of leap forward in technology.

It does. Bech32 encoding was introduced to let users use the new SegWit outputs that is was a "leap forward in technology".

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but for example you can't do bip38 with bech32 as that is not defined in the bip38 standard. so if you do try and do it then you're not going by any bip you're making something up that no one else might know how you did it or have to follow if they tried to implement the same thing. which is kind of a shame because bip38 was pretty cool. but you definitely can't do that with bech32.

It depends on what you are doing. If it is for personal encryption then you can easily make a tiny modification in BIP38 and use bech32 address. If it is a wallet that people use, again you can add that option and people will both see the algorithm and can always use it to encrypt/decrypt their keys using that wallet.

larry_vw_1955

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That's the inherent property of mnemonics that lack address type indication (and a lot more such as derivation path). Existence of different address types is not a problem here.

I don't really see the benefit of new address types that represent the same old public key. they incentived using bech32 but that doesn't mean really that its better. or represents any kind of leap forward in technology. i'm not worried about error checking because i know how to use a clipboard and qrcode reader/scanner.

but for example you can't do bip38 with bech32 as that is not defined in the bip38 standard. so if you do try and do it then you're not going by any bip you're making something up that no one else might know how you did it or have to follow if they tried to implement the same thing. which is kind of a shame because bip38 was pretty cool. but you definitely can't do that with bech32.

pooya87

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Quote from: PrimeNumber7 on October 28, 2021, 04:43:57 AM

The more address types there are, the greater the chance someone messes something up when trying to create some 3rd party application, or otherwise. If you are a user of this 3rd party application, this will negatively affect you, and if you are a bitcoin user, this has the potential to reflect negatively on bitcoin.

First of all saying "3rd party application" suggests there is a centralized authority that produces bitcoin related applications and anybody else is a third party which doesn't make any sense.
Secondly if a developer is not capable of correct implementation of a simple encoding and by extension address validation, then you have so much more serious things to worry about in all parts of that application than existence of multiple address types and encoding algorithms!

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Also, if you are trying to recover your wallet from their seed, having multiple address types adds complexity to the process, and may make some people erroneously believe there is a problem with their seed when they use their seed backup to generate the wrong address type.

That's the inherent property of mnemonics that lack address type indication (and a lot more such as derivation path). Existence of different address types is not a problem here.

PrimeNumber7

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Quote from: pooya87 on October 28, 2021, 02:19:57 AM

Quote from: larry_vw_1955 on October 28, 2021, 01:35:48 AM

i dont understand why they needed to have bech32m if they already have bech32. the more address types that get created i think the worse that is for bitcoin not better. i dont know if anyone else feel that way or not especially though if the address type that is being changed had some type of issue with it that motivated the creation of a related address typing. but i guess they'll keep going. watch out for bech32P anytime soon.

You don't have to worry about anything, in the end you are just copying a string that if nobody had mentioned you wouldn't even know it is a modified encoding scheme! Your wallet does everything behind the scene for you. If it were necessary we would introduce bech32 a to z.

The more address types there are, the greater the chance someone messes something up when trying to create some 3rd party application, or otherwise. If you are a user of this 3rd party application, this will negatively affect you, and if you are a bitcoin user, this has the potential to reflect negatively on bitcoin.

Also, if you are trying to recover your wallet from their seed, having multiple address types adds complexity to the process, and may make some people erroneously believe there is a problem with their seed when they use their seed backup to generate the wrong address type.

ABCbits

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Quote from: Coding Enthusiast on October 27, 2021, 10:48:14 AM

The actual checksum used in encoding is the result of "polymod" XORed with a constant. This constant is 0x01 for Bech32 (BIP-173) encoding just flipping the least significant bit and is 0x2bc830a3 for Bech32m (BIP-350) encoding. The former is used for witness version 0 addresses and the later for 1+. This is basically the only difference that was introduced in BIP-350.

Thanks for the explanation, it's simpler than i think. Guess i missed it because BIP 173 never use word "constant" when they mention 0x01.

Quote from: larry_vw_1955 on October 28, 2021, 01:35:48 AM

Quote from: ?? on ??

@Coding Enthusiast do you have any plan to create Bech32m version of this guide since the BIP already created and few wallet already implement it?

i dont understand why they needed to have bech32m if they already have bech32. the more address types that get created i think the worse that is for bitcoin not better. i dont know if anyone else feel that way or not especially though if the address type that is being changed had some type of issue with it that motivated the creation of a related address typing. but i guess they'll keep going. watch out for bech32P anytime soon. Angry

Here's why. On a side note, most people won't be able to tell difference between Bech32 and Bech32m. At least unless they know Bech32m is used since witness version 1 which indicated by Bech32 address with prefix bc1p.

Quote from: https://github.com/bitcoin/bips/blob/master/bip-0350.mediawiki

Motivation

BIP173 defined a generic checksummed base 32 encoded format called Bech32. It is in use for segregated witness outputs of version 0 (P2WPKH and P2WSH, see BIP141), and other applications.

Bech32 has an unexpected weakness: whenever the final character is a 'p', inserting or deleting any number of 'q' characters immediately preceding it does not invalidate the checksum. This does not affect existing uses of witness version 0 BIP173 addresses due to their restriction to two specific lengths, but may affect future uses and/or other applications using the Bech32 encoding.

This document addresses that by specifying Bech32m, a variant of Bech32 that mitigates this insertion weakness and related issues.

NotATether

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Quote from: larry_vw_1955 on October 28, 2021, 01:35:48 AM

The more address types that get created i think the worse that is for bitcoin not better.

It only really matters to developers. Normal users who are just sending and receiving bitcoin will not care much about the address as long as it is accepted at the places they need to pay (so could be a problem in the early months of deployment but as time passes it should largely become a non-issue).

pooya87

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Quote from: larry_vw_1955 on October 28, 2021, 01:35:48 AM

i dont understand why they needed to have bech32m if they already have bech32. the more address types that get created i think the worse that is for bitcoin not better. i dont know if anyone else feel that way or not especially though if the address type that is being changed had some type of issue with it that motivated the creation of a related address typing. but i guess they'll keep going. watch out for bech32P anytime soon.

You don't have to worry about anything, in the end you are just copying a string that if nobody had mentioned you wouldn't even know it is a modified encoding scheme! Your wallet does everything behind the scene for you. If it were necessary we would introduce bech32 a to z.

larry_vw_1955

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Quote from: ?? on ??

@Coding Enthusiast do you have any plan to create Bech32m version of this guide since the BIP already created and few wallet already implement it?

i dont understand why they needed to have bech32m if they already have bech32. the more address types that get created i think the worse that is for bitcoin not better. i dont know if anyone else feel that way or not especially though if the address type that is being changed had some type of issue with it that motivated the creation of a related address typing. but i guess they'll keep going. watch out for bech32P anytime soon. Angry

MixMAx123

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Quote from: oosinoots on October 25, 2021, 07:57:28 AM

How do I compute the checksum? The bip 173 page has the code in python which I do not understand. Can you explain the process so I could code in Java/Kotlin?

Here it is in Java
https://github.com/MrMaxweII/Bitcoin-Address-Generator/blob/master/src/BTClib3001/Bech32Address.java

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Quote from: oosinoots on October 25, 2021, 07:57:28 AM

How do I compute the checksum? The bip 173 page has the code in python which I do not understand. Can you explain the process so I could code in Java/Kotlin?

I haven't seen a Java/Kotlic implementation but apart from the C implementation there is JavaScript and my own C# implementations that are similar languages.

The process is:
"Expand HRP" by converting its N base-256 (8-bit) representation to 2N+1 base-32 (5-bit).
For example bc which is 0x6263 or 0b01100010_01100011 becomes 0x0303000203
In this process for each octet the highest 3 bits are placed in first half of the result and the remaining (low) 5 bits in second half. In the example above:
b=0x62=0b01100010 -> 0x0303000203 and
c=0x63=0b01100011 -> 0x0303000203
The two halves are separated with a zero (the value at the middle is always 0) -> 0x0303000203

Now we can compute checksum of [expanded HRP] | [base32 data] | [6x zeros] (note that "|" is concatenation).
The process is best explained by code

Code:

private static uint Polymod(byte[] data)
{
    uint chk = 1;
    foreach (byte b in data)
    {
        uint temp = chk >> 25;
        chk = ((chk & 0x1ffffff) << 5) ^ b;
        for (int i = 0; i < 5; i++)
        {
            if (((temp >> i) & 1) == 1)
            {
                chk ^= generator[i];
            }
        }
    }
    return chk;
}

The actual checksum used in encoding is the result of "polymod" XORed with a constant. This constant is 0x01 for Bech32 (BIP-173) encoding just flipping the least significant bit and is 0x2bc830a3 for Bech32m (BIP-350) encoding. The former is used for witness version 0 addresses and the later for 1+. This is basically the only difference that was introduced in BIP-350.

odolvlobo

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Quote from: oosinoots on October 25, 2021, 07:57:28 AM

How do I compute the checksum? The bip 173 page has the code in python which I do not understand. Can you explain the process so I could code in Java/Kotlin?

The BIP also links to a C version if that helps: https://github.com/sipa/bech32/tree/master/ref/c

oosinoots

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How do I compute the checksum? The bip 173 page has the code in python which I do not understand. Can you explain the process so I could code in Java/Kotlin?

Headphones

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Thank you for this! It's now working Cheesy

Quote from: Coding Enthusiast on July 03, 2020, 01:14:19 AM

Quote from: Headphones on July 02, 2020, 03:34:13 PM

I'm trying to decode a bech32 address tb1qwm3dqje4wc7cs2u9sv39yh2as8ae0ntzqkjunw into the h160 of the public key

Same process steps in reverse:
Map each character to its index in Bech-32 charset after removing hrp (q=0; w=14,...):

Code:

0 14 27 17 13 0 18...

The result is in base-32 (5-bits group) and has to be converted back to base-256 (8-bits or 1 octet/byte group).
Also since this is an address, the first item is the witness version that has to be dropped and evaluated separately.

Code:

Select 8-bits at a time:

Code:

01110110 11100010 11010000 01001011 ...
118      226      208      75 ...

which is 0x76e2d0... in hex and the same result that the site you linked gives.

PS. The additional steps to expand H.R.P and compute and verify checksum are skipped for simplicity but are mandatory.

Quote from: Headphones on July 02, 2020, 03:34:13 PM

How do I go from the array of numbers into the hex version of the h160 which according to https://slowli.github.io/bech32-buffer/ should be: 751e76e8199196d454941c45d1b3a323f1433bd6

Try again, when decoding Bech32=tb1qwm3dqje4wc7cs2u9sv39yh2as8ae0ntzqkjunw it returns 0x76e2d04b35763d882b858322525d5d81fb97cd62 as data (hexadecimal).

Coding Enthusiast

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Quote from: Headphones on July 02, 2020, 03:34:13 PM

I'm trying to decode a bech32 address tb1qwm3dqje4wc7cs2u9sv39yh2as8ae0ntzqkjunw into the h160 of the public key

Same process steps in reverse:
Map each character to its index in Bech-32 charset after removing hrp (q=0; w=14,...):

Code:

0 14 27 17 13 0 18...

The result is in base-32 (5-bits group) and has to be converted back to base-256 (8-bits or 1 octet/byte group).
Also since this is an address, the first item is the witness version that has to be dropped and evaluated separately.

Code:

Select 8-bits at a time:

Code:

01110110 11100010 11010000 01001011 ...
118      226      208      75 ...

which is 0x76e2d0... in hex and the same result that the site you linked gives.

PS. The additional steps to expand H.R.P and compute and verify checksum are skipped for simplicity but are mandatory.

Quote from: Headphones on July 02, 2020, 03:34:13 PM

How do I go from the array of numbers into the hex version of the h160 which according to https://slowli.github.io/bech32-buffer/ should be: 751e76e8199196d454941c45d1b3a323f1433bd6

Try again, when decoding Bech32=tb1qwm3dqje4wc7cs2u9sv39yh2as8ae0ntzqkjunw it returns 0x76e2d04b35763d882b858322525d5d81fb97cd62 as data (hexadecimal).

Headphones

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Hey, great post! It's really useful.

I'm trying to decode a bech32 address tb1qwm3dqje4wc7cs2u9sv39yh2as8ae0ntzqkjunw into the h160 of the public key, which is step 3 in your guide, using the reference implementation in python.

I end up with an array of integers: [118, 226, 208, 75, 53, 118, 61, 136, 43, 133, 131, 34, 82, 93, 93, 129, 251, 151, 205, 98] which I think corresponds with step 4 of your guide.

How do I go from the array of numbers into the hex version of the h160 which according to https://slowli.github.io/bech32-buffer/ should be: 751e76e8199196d454941c45d1b3a323f1433bd6

Any help would be appreciated!

Coding Enthusiast

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Quote from: MixMAx123 on February 25, 2020, 02:01:57 PM

What am I doing wrong?

The encoding is Bech-32 not Base-58 and there is no SHA256 in this encoding, there is only playing around with bits. Read BIP-173 for details of how you should compute the checksum.

MixMAx123

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I have now successfully reached step 5.
I have: 000e140f070d1a001912060b0d081504140311021d030c1d03040f1814060e1e16

Now I do not come to step 6.
When I calculate: SHA256 (SHA256 (000e140f070d1a001912060b0d081504140311021d030c1d03040f1814060e1e16)) = 103ede5cc41abfd088a368bb40df3d52e5614460521d88daa202917c7f3de88d.

The first 6 bytes are then with me: 10 3e de 5c c4 1a
And this is a different number than yours.
What am I doing wrong?

TsaPaka

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Thank you because I could understand until the last soft fork.
I explain here how a segwit address in P2WSH format is derived so as not to mix the segwit between P2WPKH and P2WSH.
Note that the guide explained above generates in P2WPKH format about 42 characters but P2WSH format about 62 characters.

https://bitcointalksearch.org/topic/step-by-step-guide-to-go-from-public-key-to-a-p2wsh-bech32-encoded-address-5227953

denisdo95

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Quote from: DannyHamilton on November 23, 2019, 11:17:04 PM

Here's a simple way to understand it...

Convert the first value from a hex value to an array of bits where: 0 = 0000, 1=0001, 2=0010, 3-0011, 4=0100, etc
7 5 1 e 7 6 e ...
0111 0101 0001 1110 0111 0110 1110 ...

Change the spacing of the 1's and zeros so that they are grouped 5 in a set instead of 4:
01110 10100 01111 00111 01101 110 ...

Convert each set of 5 into a hex value:
01110 10100 01111 00111 01101 110...
0e 14 0f 07 0d ...

Thank You Man! You best! Cool

Topic: Step by step guide to go from public key to a Bech32 encoded address (Read 1341 times)