Bitcoin/address validation

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Task
Bitcoin/address validation
You are encouraged to solve this task according to the task description, using any language you may know.

Write a program that takes a bitcoin address as argument, and checks whether or not this address is valid.

A bitcoin address uses a base58 encoding, which uses an alphabet of the characters 0 .. 9, A ..Z, a .. z, but without the four characters 0, O, I and l.

With this encoding, a bitcoin address encodes 25 bytes:

  • the first byte is the version number, which will be zero for this task ;
  • the next twenty bytes are a RIPEMD-160 digest, but you don't have to know that for this task: you can consider them a pure arbitrary data ;
  • the last four bytes are a checksum check. They are the first four bytes of a double SHA-256 digest of the previous 21 bytes.

To check the bitcoin address, you must read the first twenty-one bytes, compute the checksum, and check that it corresponds to the last four bytes.

The program can either return a boolean value or throw an exception when not valid.

You can use a digest library for SHA-256.

Here is an example of a bitcoin address:

1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i

It does not belong to anyone. It is part of the test suite of the bitcoin software. You can change a few characters in this string and check that it will fail the test.

extra credit: allow your code to deal with compressed keys


Contents

[edit] Ada

with Ada.Exceptions, Interfaces;
with Ada.Streams;
use Ada.Exceptions, Interfaces;
use Ada.Streams;
 
package Bitcoin is
subtype BT_Raw_Addr is Stream_Element_Array(1..25);
subtype BT_Checksum is Stream_Element_Array(1..4);
subtype BT_Addr is String(1..34);
subtype Sha256String is String(1..64);
Invalid_Address_Error : Exception;
 
function Double_Sha256(S : Stream_Element_Array) return BT_Checksum;
function Is_Valid(A : BT_Raw_Addr) return Boolean;
procedure Base58_Decode(S : BT_Addr; A : out BT_Raw_Addr) ;
private
Base58 : constant String := "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
function Hex_Val (C, C2 : Character) return Stream_Element;
end Bitcoin;
 
 
with GNAT.SHA256, Ada.Strings.Fixed;
use GNAT.SHA256, Ada.Strings.Fixed;
 
package body Bitcoin is
 
function Hex_Val (C, C2 : Character) return Stream_Element is
subtype Nibble is Integer range 0..15;
HEX : array (0..255) of Nibble := (
48=>0, 49=>1, 50=>2, 51=>3, 52=>4, 53=>5, 54=>6, 55=>7, 56=>8, 57=>9
, 65=>10, 66=>11, 67=>12, 68 =>13, 69 =>14, 70 =>15
, 97=>10, 98=>11, 99=>12, 100=>13, 101=>14, 102=>15
, Others=>0
);
begin
return Stream_Element(HEX(Character'Pos(C)) * 16 + HEX(Character'Pos(C2)));
end Hex_Val;
 
function Double_Sha256(S : Stream_Element_Array) return BT_Checksum is
Ctx  : Context := Initial_Context;
D : Message_Digest;
S2 : Stream_Element_Array(1..32);
Ctx2 : Context := Initial_Context;
C : BT_Checksum;
begin
Update(Ctx, S);
D := Digest(Ctx);
for I in S2'Range loop
S2(I) := Hex_Val(D(Integer(I)*2-1), D(Integer(I)*2));
end loop;
Update(Ctx2, S2);
D := Digest(Ctx2);
for I in C'Range loop
C(I) := Hex_Val(D(Integer(I)*2-1), D(Integer(I)*2));
end loop;
return C;
 
end Double_Sha256;
 
 
--------------------------------------------------------------------------------
-- Summary of Base58: --
-- We decode S into a 200 bit unsigned integer. --
-- We could use a BigNum library, but choose to go without. --
--------------------------------------------------------------------------------
procedure Base58_Decode(S : BT_Addr; A : out BT_Raw_Addr) is
begin
A := (Others => 0);
for I in S'Range loop
declare
P : Natural := Index(Base58, String(S(I..I)));
C : Natural;
begin
if P = 0 then
raise Invalid_Address_Error;
end if;
C := P - 1;
for J in reverse A'Range loop
C  := C + Natural(A(J)) * 58;
A(J) := Stream_Element(Unsigned_32(C) and 255); -- 0x00FF
C  := Natural(Shift_Right(Unsigned_32(C),8) and 255); -- 0xFF00
end loop;
if C /= 0 then
raise Invalid_Address_Error;
end if;
end;
end loop;
end Base58_Decode;
 
 
function Is_Valid(A : BT_Raw_Addr) return Boolean is
begin
return A(1) = 0 and A(22..25) = Double_Sha256(A(1..21));
end Is_Valid;
 
 
end Bitcoin;
 
with Ada.Text_IO, Bitcoin;
use Ada.Text_IO, Bitcoin;
 
procedure Bitcoin_Addr_Validate is
begin
declare
BTs : array (positive range <>) of BT_Addr := (
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i" -- VALID
, "1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9" -- VALID
, "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62X" -- checksum changed, original data.
, "1ANNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i" -- data changed, original checksum.
, "1A Na15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i" -- invalid chars
);
begin
for I in Bts'Range loop
declare
A : BT_Raw_Addr;
Valid : Boolean;
begin
Put(BTs(I) & " validity: ");
Base58_Decode(BTs(I), A);
Valid := Is_Valid(A);
Put_Line(Boolean'Image(Valid));
exception
when E : Invalid_Address_Error =>
Put_Line ("*** Error: Invalid BT address.");
end;
end loop;
end;
end Bitcoin_Addr_Validate;
 

Output:

1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i validity: TRUE
1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9 validity: TRUE
1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62X validity: FALSE
1ANNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i validity: FALSE
1A Na15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i validity: *** Error: Invalid BT address.

[edit] C

#include <stdio.h>
#include <string.h>
#include <openssl/sha.h>
 
const char *coin_err;
#define bail(s) { coin_err = s; return 0; }
 
int unbase58(const char *s, unsigned char *out) {
static const char *tmpl = "123456789"
"ABCDEFGHJKLMNPQRSTUVWXYZ"
"abcdefghijkmnopqrstuvwxyz";
int i, j, c;
const char *p;
 
memset(out, 0, 25);
for (i = 0; s[i]; i++) {
if (!(p = strchr(tmpl, s[i])))
bail("bad char");
 
c = p - tmpl;
for (j = 25; j--; ) {
c += 58 * out[j];
out[j] = c % 256;
c /= 256;
}
 
if (c) bail("address too long");
}
 
return 1;
}
 
int valid(const char *s) {
unsigned char dec[32], d1[SHA256_DIGEST_LENGTH], d2[SHA256_DIGEST_LENGTH];
 
coin_err = "";
if (!unbase58(s, dec)) return 0;
 
SHA256(SHA256(dec, 21, d1), SHA256_DIGEST_LENGTH, d2);
 
if (memcmp(dec + 21, d2, 4))
bail("bad digest");
 
return 1;
}
 
int main (void) {
const char *s[] = {
"1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i",
"1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nJ9",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62I",
0 };
int i;
for (i = 0; s[i]; i++) {
int status = valid(s[i]);
printf("%s: %s\n", s[i], status ? "Ok" : coin_err);
}
 
return 0;
}

[edit] D

This requires the D module from the SHA-256 Task.

Translation of: Go
import std.stdio, std.algorithm, std.array, std.string, sha_256;
 
struct A25 {
// Type for a 25 ubyte (not base58 encoded) bitcoin address.
ubyte[25] enc;
 
ubyte bitcoinVersion() const pure nothrow {
return enc[0];
}
 
ubyte[4] embeddedChecksum() const pure nothrow {
return enc[$ - 4 .. $];
}
 
/** Computes a double sha256 hash of the first 21 bytes of
the address. Returns the full 32 ubyte sha256 hash. */

ubyte[32] doubleSHA256() const pure nothrow {
return SHA256.digest(SHA256.digest(enc[0 .. 21]));
}
 
/** Returns a four ubyte checksum computed from the first 21
bytes of the address. */

ubyte[4] computeChecksum() const pure nothrow {
return doubleSHA256[0 .. 4];
}
 
/** Takes a base58 encoded address and decodes it into the
receiver. Errors are returned if the argument is not valid base58
or if the decoded value does not fit in the 25 ubyte address.
The address is not otherwise checked for validity. */

string set58(in ubyte[] s) pure nothrow {
static immutable digits =
"123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
.representation;
static assert(digits.length == 58);
 
foreach (immutable char s1; s) {
immutable c = digits.countUntil(s1);
if (c < 0)
return "found a bad char in the Bitcoin address.";
 
// Currently the D type system can't see c as nonegative.
uint uc = (c < 0) ? 0 : c;
 
foreach_reverse (ref aj; enc) {
uc += digits.length * aj;
aj = uc % 256;
uc /= 256;
}
if (uc > 0)
return "too long Bitcoin address.";
}
 
return null;
}
}
 
/** Validates a base58 encoded bitcoin address. An address is valid
if it can be decoded into a 25 ubyte address, the Version number is 0,
and the checksum validates. Return value ok will be true for valid
addresses. If ok is false, the address is invalid and the error value
may indicate why. */

string isValidA58(in ubyte[] a58) pure nothrow {
A25 a;
immutable err = a.set58(a58);
if (!err.empty)
return err;
if (a.bitcoinVersion != 0)
return "not Bitcoin version 0.";
return (a.embeddedChecksum == a.computeChecksum) ? null :
"checksums don't match.";
}
 
void main() {
immutable tests = ["1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62j",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62!",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62iz",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62izz"];
 
foreach (immutable test; tests) {
immutable err = test.representation.isValidA58;
writefln(`"%s": %s`, test, err.empty ? "OK." : err);
}
}
Output:
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i": OK.
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62j": checksums don't match.
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62!": found a bad char in the Bitcoin address.
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62iz": not Bitcoin version 0.
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62izz": too long Bitcoin address.

[edit] Erlang

Using base58 module from http://github.com/titan098/erl-base58.git.

 
-module( bitcoin_address ).
 
-export( [task/0, validate/1] ).
 
task() ->
io:fwrite( "Validate ~p~n", ["1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i"] ),
io:fwrite( "~p~n", [validate("1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i")] ),
io:fwrite( "Validate ~p~n", ["1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW622"] ),
io:fwrite( "~p~n", [validate("1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW622")] ).
 
validate( String ) ->
{length_25, <<Address:21/binary, Checksum:4/binary>>} = {length_25, base58:base58_to_binary( String )},
<<Version:1/binary, _/binary>> = Address,
{version_0, <<0>>} = {version_0, Version},
<<Four_bytes:4/binary, _T/binary>> = crypto:hash( sha256, crypto:hash(sha256, Address) ),
{checksum, Checksum} = {checksum, Four_bytes},
ok.
 
Output:
17>  bitcoin_address:task().
Validate "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i"
ok
Validate "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW622"
** exception error: no match of right hand side value {checksum,<<"ÀF²ÿ">>}
     in function  bitcoin_address:validate/1 (src/bitcoin_address.erl, line 16)
     in call from bitcoin_address:task/0 (src/bitcoin_address.erl, line 9)

[edit] Go

Translation of: C
package main
 
import (
"bytes"
"crypto/sha256"
"errors"
"os"
)
 
// With at least one other bitcoin RC task, this source is styled more like
// a package to show how functions of the two tasks might be combined into
// a single package. It turns out there's not really that much shared code,
// just the A25 type and doubleSHA256 method, but it's enough to suggest how
// the code might be organized. Types, methods, and functions are capitalized
// where they might be exported from a package.
 
// A25 is a type for a 25 byte (not base58 encoded) bitcoin address.
type A25 [25]byte
 
func (a *A25) Version() byte {
return a[0]
}
 
func (a *A25) EmbeddedChecksum() (c [4]byte) {
copy(c[:], a[21:])
return
}
 
// DoubleSHA256 computes a double sha256 hash of the first 21 bytes of the
// address. This is the one function shared with the other bitcoin RC task.
// Returned is the full 32 byte sha256 hash. (The bitcoin checksum will be
// the first four bytes of the slice.)
func (a *A25) doubleSHA256() []byte {
h := sha256.New()
h.Write(a[:21])
d := h.Sum([]byte{})
h = sha256.New()
h.Write(d)
return h.Sum(d[:0])
}
 
// ComputeChecksum returns a four byte checksum computed from the first 21
// bytes of the address. The embedded checksum is not updated.
func (a *A25) ComputeChecksum() (c [4]byte) {
copy(c[:], a.doubleSHA256())
return
}/* {{header|Go}} */
 
// Tmpl and Set58 are adapted from the C solution.
// Go has big integers but this techinique seems better.
var tmpl = []byte("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")
 
// Set58 takes a base58 encoded address and decodes it into the receiver.
// Errors are returned if the argument is not valid base58 or if the decoded
// value does not fit in the 25 byte address. The address is not otherwise
// checked for validity.
func (a *A25) Set58(s []byte) error {
for _, s1 := range s {
c := bytes.IndexByte(tmpl, s1)
if c < 0 {
return errors.New("bad char")
}
for j := 24; j >= 0; j-- {
c += 58 * int(a[j])
a[j] = byte(c % 256)
c /= 256
}
if c > 0 {
return errors.New("too long")
}
}
return nil
}
 
// ValidA58 validates a base58 encoded bitcoin address. An address is valid
// if it can be decoded into a 25 byte address, the version number is 0,
// and the checksum validates. Return value ok will be true for valid
// addresses. If ok is false, the address is invalid and the error value
// may indicate why.
func ValidA58(a58 []byte) (ok bool, err error) {
var a A25
if err := a.Set58(a58); err != nil {
return false, err
}
if a.Version() != 0 {
return false, errors.New("not version 0")
}
return a.EmbeddedChecksum() == a.ComputeChecksum(), nil
}
 
// Program returns exit code 0 with valid address and produces no output.
// Otherwise exit code is 1 and a message is written to stderr.
func main() {
if len(os.Args) != 2 {
errorExit("Usage: valid <base58 address>")
}
switch ok, err := ValidA58([]byte(os.Args[1])); {
case ok:
case err == nil:
errorExit("Invalid")
default:
errorExit(err.Error())
}
}
 
func errorExit(m string) {
os.Stderr.WriteString(m + "\n")
os.Exit(1)
}
Output:

Command line usage examples showing program exit status.

> valid ; echo $status
Usage: valid <base58 address>
1
> valid 1 1 ; echo $status
Usage: valid <base58 address>
1
> valid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i ; echo $status
0
> valid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62j ; echo $status
Invalid
1
> valid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62! ; echo $status
bad char
1
> valid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62iz ; echo $status
not version 0
1
> valid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62izz ; echo $status
too long
1


[edit] Perl

Translation of: C
my @b58 = qw{
1 2 3 4 5 6 7 8 9
A B C D E F G H J K L M N P Q R S T U V W X Y Z
a b c d e f g h i j k m n o p q r s t u v w x y z
};
my %b58 = map { $b58[$_] => $_ } 0 .. 57;
 
sub unbase58 {
use integer;
my @out;
for my $c ( map { $b58{$_} } shift =~ /./g ) {
for (my $j = 25; $j--; ) {
$c += 58 * ($out[$j] // 0);
$out[$j] = $c % 256;
$c /= 256;
}
}
return @out;
}
 
sub check_bitcoin_address {
# does nothing if the address is valid
# dies otherwise
use Digest::SHA qw(sha256);
my @byte = unbase58 shift;
die "wrong checksum" unless
join('', map { chr } @byte[21..24]) eq
substr sha256(sha256 pack 'C*', @byte[0..20]), 0, 4;
}

[edit] Perl 6

Translation of: C
enum B58 <
1 2 3 4 5 6 7 8 9
A B C D E F G H J K L M N P Q R S T U V W X Y Z
a b c d e f g h i j k m n o p q r s t u v w x y z
>;
 
sub unbase58(Str $str) {
my @out = 0 xx 25;
for B58.enums.hash{$str.comb} {
my $c = $_;
for reverse ^25 {
$c += 58 * @out[$_];
@out[$_] = $c % 256;
$c div= 256;
}
}
return @out;
}
 
sub check-bitcoin-address($addr) {
use Digest::SHA;
my @byte = unbase58 $addr;
!!! 'wrong checksum' unless @byte[21..24] ~~
sha256(sha256 Buf.new: @byte[0..20]).subbuf(0, 4).list;
}

[edit] PicoLisp

(setq *Alphabet 
(chop "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"))
 
# if returns NIL then adress is already invalid
(de base58 (Str)
(let N 0
(for L (chop Str)
(setq N
(+
(* N 58)
(index L *Alphabet)
-1 ) ) )
 
N )
)
 
(de sha256 (Lst)
(native "libcrypto.so" "SHA256"
'(B . 32)
(cons
NIL
(32)
(native "libcrypto.so" "SHA256" '(B . 32)
(cons NIL (32) Lst) (length Lst) '(NIL (32))) )
32
'(NIL (32)) ) )
 
(de bytes25 (N)
(flip
(make
(do 25
(link (% N 256))
(setq N (/ N 256)) ) ) ) )
 
(de valid (Str)
(and
(base58 Str)
(bytes25 @)
(=
(head 4 (sha256 (head 21 @)))
(tail 4 @) ) ) )
 
(bye)

[edit] Python

from hashlib import sha256
 
digits58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
 
def decode_base58(bc, length):
n = 0
for char in bc:
n = n * 58 + digits58.index(char)
return n.to_bytes(length, 'big')
 
def check_bc(bc):
bcbytes = decode_base58(bc, 25)
return bcbytes[-4:] == sha256(sha256(bcbytes[:-4]).digest()).digest()[:4]
 
if __name__ == '__main__':
bc = '1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i'
assert check_bc(bc)
assert not check_bc( bc.replace('N', 'P', 1) )
assert check_bc('1111111111111111111114oLvT2')
assert check_bc("17NdbrSGoUotzeGCcMMCqnFkEvLymoou9j")
Output:

No output signifying success.

Help
For those looking at examples here to try and work out what is required, the n.to_bytes() call is equivalent to this code which converts a (long) integer into individual bytes of a byte array in a particular order:
>>> n = 2491969579123783355964723219455906992268673266682165637887
>>> length = 25
>>> list( reversed(range(length)) )
[24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> assert n.to_bytes(length, 'big') == bytes( (n >> i*8) & 0xff for i in reversed(range(length)))
>>>

[edit] Racket

 
#lang racket/base
 
;; Same sha-256 interface as the same-named task
(require ffi/unsafe ffi/unsafe/define openssl/libcrypto)
(define-ffi-definer defcrypto libcrypto)
(defcrypto SHA256_Init (_fun _pointer -> _int))
(defcrypto SHA256_Update (_fun _pointer _pointer _long -> _int))
(defcrypto SHA256_Final (_fun _pointer _pointer -> _int))
(define (sha256 bytes)
(define ctx (malloc 128))
(define result (make-bytes 32))
(SHA256_Init ctx)
(SHA256_Update ctx bytes (bytes-length bytes))
(SHA256_Final result ctx)
result)
 
;; base58 decoding
(define base58-digits
(let ([v (make-vector 128 #f)])
(for ([i (in-naturals)]
[c "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"])
(vector-set! v (char->integer c) i))
v))
(define (base58->integer str)
(for/fold ([n 0]) ([c str])
(+ (* n 58) (vector-ref base58-digits (char->integer c)))))
 
(define (int->bytes n digits)
(list->bytes (let loop ([n n] [digits digits] [acc '()])
(if (zero? digits) acc
(let-values ([(q r) (quotient/remainder n 256)])
(loop q (sub1 digits) (cons r acc)))))))
 
(define (validate-bitcoin-address str)
(define bs (int->bytes (base58->integer str) 25))
(equal? (subbytes (sha256 (sha256 (subbytes bs 0 21))) 0 4)
(subbytes bs 21)))
 
;; additional tests taken from the other solutions
(validate-bitcoin-address "1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i") ; => #t
(validate-bitcoin-address "1111111111111111111114oLvT2")  ; => #t
(validate-bitcoin-address "17NdbrSGoUotzeGCcMMCqnFkEvLymoou9j") ; => #t
(validate-bitcoin-address "1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9") ; => #t
(validate-bitcoin-address "1badbadbadbadbadbadbadbadbadbadbad") ; => #f
 

[edit] Tcl

Library: Tcllib (Package: sha256)
package require sha256
 
# Generate a large and boring piece of code to do the decoding of
# base58-encoded data.
apply {{} {
set chars "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
set i -1
foreach c [split $chars ""] {
lappend map $c "return -level 0 [incr i]"
}
lappend map default {return -code error "bad character \"$c\""}
proc base58decode str [string map [list @BODY@ [list $map]] {
set num 0
set count [expr {ceil(log(58**[string length $str])/log(256))}]
foreach c [split $str {}] {
set num [expr {$num*58+[switch $c @BODY@]}]
}
for {set i 0} {$i < $count} {incr i} {
append result [binary format c [expr {$num & 255}]]
set num [expr {$num >> 8}]
}
return [string reverse $result]
}]
}}
 
# How to check bitcoin address validity
proc bitcoin_addressValid {address} {
set a [base58decode $address]
set ck [sha2::sha256 -bin [sha2::sha256 -bin [string range $a 0 end-4]]]
if {[string range $a end-3 end] ne [string range $ck 0 3]} {
return -code error "signature does not match"
}
return "$address is ok"
}

Testing if it works

puts [bitcoin_addressValid 1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9]
puts [bitcoin_addressValid 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i]
Output:
1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9 is ok
1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i is ok

[edit] UNIX Shell

Works with: bash
base58=({1..9} {A..H} {J..N} {P..Z} {a..k} {m..z})
bitcoinregex="^[$(printf "%s" "${base58[@]}")]{34}$"
 
decodeBase58() {
local s=$1
for i in {0..57}
do s="${s//${base58[i]}/ $i}"
done
dc <<< "16o0d${s// /+58*}+f"
}
 
checksum() {
xxd -p -r <<<"$1" |
openssl dgst -sha256 -binary |
openssl dgst -sha256 -binary |
xxd -p -c 80 |
head -c 8
}
 
checkBitcoinAddress() {
if [[ "$1" =~ $bitcoinregex ]]
then
h=$(decodeBase58 "$1")
checksum "00${h::${#h}-8}" |
grep -qi "^${h: -8}$"
else return 2
fi
}

[edit] zkl

Uses shared library zklMsgHash.

var MsgHash=Import("zklMsgHash");
const symbols = "123456789" // 58 characters: no cap i,o; ell, zero
"ABCDEFGHJKLMNPQRSTUVWXYZ"
"abcdefghijkmnopqrstuvwxyz";
 
fcn unbase58(str){ // --> Data (byte bucket)
out:=(0).pump(25,Data,0);
str.pump(Void,symbols.index,'wrap(n){
[24..0,-1].reduce('wrap(c,idx){
c+=58*out[idx];
out[idx]=c;
c/256;
},n) : if(_) throw(Exception.ValueError("address too long"));
});
out;
}
 
fcn coinValide(addr){
reg dec; try{ dec=unbase58(addr) }catch{ return(False) }
// hash twice, once each time --> binary hash (instead of hex string)
d1:=MsgHash.SHA256(MsgHash.SHA256(dec[0,21],1,False),1,False);
d1[0,4]==dec[-4,*]; // two byte blobs
}
T("1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i","1Q1pE5vPGEEMqRcVRMbtBK842Y6Pzo6nK9",
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62X", // checksum changed, original data.
"1ANNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i", // data changed, original checksum.
"1A Na15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i", // invalid chars
"1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62izz", // too long
).apply(coinValide).println();
Output:
L(True,True,False,False,False,False)
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