substitution cipher implementation

Reads in a json file that has a map of letters to letters

main.go

@@ -15,13 +15,15 @@ func init() {
 }
 
 func main() {
+	psyfer.ReadConfig()
+	psyfer.Substitution("hello")
 	var input string
 	var cipher string
 	var cipType string
 	var key string
 
 	var encrypt = &cobra.Command{
-		Use:   "encrypt [cipher] [key] [input]",
+		Use:   "encrypt -c [cipher] -k [key] -i [input]",
 		Short: "encrypt string",
 		Long:  `encrypt given string`,
 		Run: func(cmd *cobra.Command, args []string) {
@@ -52,7 +54,7 @@ func main() {
 	}
 
 	var decrypt = &cobra.Command{
-		Use:   "decrypt [cipher] [key] [input]",
+		Use:   "decrypt -c [cipher] -k [key] -i [input]",
 		Short: "decrypt string",
 		Long:  `decrypt given string`,
 		Run: func(cmd *cobra.Command, args []string) {

psyfer/substitution.go

@@ -1,4 +1,36 @@
 package psyfer
 
-func ReadConfig() {
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+)
+
+type KeyJSON struct {
+	Key map[string]string `json:"key"`
+}
+
+var k = KeyJSON{}
+
+func ReadConfig() {
+	dat, err := ioutil.ReadFile("key.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+	json.Unmarshal([]byte(dat), &k)
+	fmt.Println(k.Key["a"])
+}
+
+func Substitution(input string) string {
+	inputSlice := []string{}
+	output := ""
+	for _, char := range input {
+		inputSlice = append(inputSlice, string(char))
+	}
+	for i := range inputSlice {
+		output += k.Key[inputSlice[i]]
+	}
+	fmt.Println(output)
+	return output
 }