script error bash ( error:*** WARNING : deprecated key derivation used)

Question

#!/bin/bash

# Decrypt function
function decrypt {
    MzSaas7k=$(echo $hash | sed 's/988sn1/83unasa/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/4d298d/9999/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/3i8dqos82/873h4d/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/4n9Ls/20X/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/912oijs01/i7gg/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/k32jx0aa/n391s/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/nI72n/YzF1/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/82ns71n/2d49/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/JGcms1a/zIm12/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/MS9/4SIs/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/Ymxj00Ims/Uso18/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/sSi8Lm/Mit/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/9su2n/43n92ka/g')
    Mzns7293sk=$(echo $MzSaas7k | sed 's/ggf3iunds/dn3i8/g')
    MzSaas7k=$(echo $Mzns7293sk | sed 's/uBz/TT0K/g')

    flag=$(echo $MzSaas7k | base64 -d | openssl enc -aes-128-cbc -a -d -salt -pass pass:$salt)
}

# Variables
var="9M"
salt=""
hash="VTJGc2RHVmtYMTl2ZnYyNTdUeERVRnBtQWVGNmFWWVUySG1wTXNmRi9rQT0K"

# Base64 Encoding Example:
#        $ echo "Some Text" | base64

for i in {1..28}

do

    var=$(echo $var | base64)
    
    if [[ $i == 28 ]]
    then
        salt=$(echo $var | wc -c)
    fi    
done

# Check if $salt is empty
if [[ ! -z "$salt" ]]
then
    decrypt
    echo $flag
else
    exit 1
fi

error:*** WARNING : deprecated key derivation used. Using -iter or -pbkdf2 would be better. bad decrypt 140546881238400:error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt:../crypto/evp/evp_enc.c:610:

the exercise: Create a "For" loop that encodes the variable "var" 28 times in "base64". The number of characters in the 28th hash is the value that must be assigned to the "salt" variable. code made by me :

for i in {1..28}

do

    var=$(echo $var | base64)

    if [[ $i == 28 ]]
    then
        salt=$(echo $var | wc -c)
    fi    
done

Answer 1

It should be right, but I had to make a workaround too.

This might do the trick:

salt=$((${#var}+1))
# ${#var} counts the length and you have to add 1 to make the exercise work.

This way it'll still show you the warning, but if you copy the last line, that'll be your answer.