I hate PoW on CTF

pass_pow.go

package main

import (
    "fmt"
    "os"
    "hash"
    "strings"
    "crypto/MD5"
    "crypto/SHA1"
    "crypto/SHA256"
    "crypto/SHA512"
)

var (
    chars string = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
)

func Usage() {
    fmt.Println("Usage PoW")
    fmt.Println("$ ./Pow TARGET HASH-FUNCTION")
    fmt.Println("")
    fmt.Println("Hash Funcionts:")
    fmt.Println("MD5, SHA1, SHA224, SHA256, SHA384, SHA512")
    fmt.Println("")
    fmt.Println("Example:")
    fmt.Println("\t$ ./PoW 0da3 md5\n")
}

func GetHash(val, algorithm string) []byte {
    var hashData []byte
    var hasher hash.Hash

    switch algorithm {
    case "md5", "MD5":
        hasher = md5.New()
    case "sha1", "SHA1":
        hasher = sha1.New()
    case "sha224", "SHA224":
        hasher = sha256.New224()
    case "sha256", "SHA256":
        hasher = sha256.New()
    case "sha384", "SHA384":
        hasher = sha512.New384()
    case "sha512", "SHA512":
        hasher = sha512.New()
    default:
        hasher = sha256.New()
    }

    hasher.Write([]byte(val))
    hashData = hasher.Sum(nil)
    return hashData
}

func PoW(target, algorthm string) string {
    var str, hashString string
    for _, ch1  := range(chars) {
        for _, ch2  := range(chars) {
            for _, ch3  := range(chars) {
                for _, ch4  := range(chars) {
                    str = fmt.Sprintf("%s%s%s%s",
                        string(ch1), string(ch2), string(ch3), string(ch4))
                    hashString = fmt.Sprintf("%x", GetHash(str, algorthm))
                    tmp := hashString[len(hashString)-len(target):]
                    if strings.Compare(tmp, target) == 0 {
                        return str
                    }
                }
            }
        }
    }
    return ""
}

func main() {
    if len(os.Args) < 3 {
        Usage()
        os.Exit(1)
    }
    fmt.Println(PoW(os.Args[1], os.Args[2]))
}