How to resolve the algorithm Bitcoin/public point to address step by step in the Tcl programming language

Published on 12 May 2024 09:40 PM
#Tcl

How to resolve the algorithm Bitcoin/public point to address step by step in the Tcl programming language

Table of Contents

Problem Statement

Bitcoin uses a specific encoding format to encode the digest of an elliptic curve public point into a short ASCII string. The purpose of this task is to perform such a conversion. The encoding steps are: The base-58 encoding is based on an alphabet of alphanumeric characters (numbers, upper case and lower case, in that order) but without the four characters 0, O, l and I. Here is an example public point: The corresponding address should be: 16UwLL9Risc3QfPqBUvKofHmBQ7wMtjvM Nb. The leading '1' is not significant as 1 is zero in base-58. It is however often added to the bitcoin address for various reasons. There can actually be several of them. You can ignore this and output an address without the leading 1. Extra credit: add a verification procedure about the public point, making sure it belongs to the secp256k1 elliptic curve

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Bitcoin/public point to address step by step in the Tcl programming language

Source code in the tcl programming language

package require ripemd160
package require sha256

# Exactly the algorithm from https://en.bitcoin.it/wiki/Base58Check_encoding
proc base58encode data {
    set digits "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
    for {set zeroes 0} {[string index $data 0] eq "\x00"} {incr zeroes} {
	set data [string range $data 1 end]
    }
    binary scan $data "H*" hex
    scan $hex "%llx" num
    for {set out ""} {$num > 0} {set num [expr {$num / 58}]} {
	append out [string index $digits [expr {$num % 58}]]
    }
    append out [string repeat [string index $digits 0] $zeroes]
    return [string reverse $out]
}

# Encode a Bitcoin address
proc bitcoin_mkaddr {A B} {
    set A [expr {$A & ((1<<256)-1)}]
    set B [expr {$B & ((1<<256)-1)}]
    set bin [binary format "cH*" 4 [format "%064llx%064llx" $A $B]]
    set md [ripemd::ripemd160 [sha2::sha256 -bin $bin]]
    set addr [binary format "ca*" 0 $md]
    set hash [sha2::sha256 -bin [sha2::sha256 -bin $addr]]
    append addr [binary format "a4" [string range $hash 0 3]]
    return [base58encode $addr]
}


puts [bitcoin_mkaddr \
	0x50863AD64A87AE8A2FE83C1AF1A8403CB53F53E486D8511DAD8A04887E5B2352 \
	0x2CD470243453A299FA9E77237716103ABC11A1DF38855ED6F2EE187E9C582BA6]

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