Bitcoin/address validation

You are encouraged to solve this task according to the task description, using any language you may know.


Task

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   zero
   O   uppercase oh
   I   uppercase eye
   l   lowercase ell


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.



Example of a bitcoin address



1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i



It doesn't belong to anyone and is part of the test suite of the bitcoin software.

You can change a few characters in this string and check that it'll fail the test.




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
}