Tkinter - converting a result - python-3.x

Question

I am converting base64 to a string(complete) and I want to be able to edit the converted string entry and have this show up as the amended base64 i.e. input the #commented string below, click enter and then set "alg" to None in the second box and then have this amendment appear in the top / bottom box.
Note: I added the third box to compare whether the b64 results - it would be easier to change the results in the top box to reflect any amendments
import base64
import binascii
from tkinter import *
#eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
root = Tk()
root.title("Converter")
root.geometry('290x200+250+60')
def b64decode():
s = strentry.get()
try:
return(res1.set(base64.b64decode(s).decode()))
except:
return(res.set("Error"))
def string_to_b64():
data = res1.get()
encodedBytes = base64.b64encode(data.encode("utf-8"))
encodedStr = str(encodedBytes, "utf-8")
return(res3.set(encodedStr))
strentry= StringVar()
res = StringVar()
res1 = StringVar()
res3 = StringVar()
Enter_Value_Entry = Entry(root, text="", textvariable = strentry)
Enter_Value_Entry.pack()
Enter_Value_Entry2 = Entry(root, textvariable = res1)
Enter_Value_Entry2.pack()
Enter_Value_Entry2 = Entry(root, textvariable = res3)
Enter_Value_Entry2.pack()
Error = Label(root,textvariable=res)
Error.pack()
root.bind("<Return>", lambda event: b64decode()==string_to_b64())
root.mainloop()

Answer 1

It is not advisable to try to edit Base64 unless you handle every bite by 8 & 6's
You say you want to just target a chunk so here it is laid out what the needful change must consider.
text as txt {"alg" :"HS25 6","ty p":"JW T"}
text as b64 eyJhbGci OiJIUzI1 NiIsInR5 cCI6IkpX VCJ9
change bytes of {"alg" to {"nul" no problem only first block is changed
text as txt {"nul" :"HS25 6","ty p":"JW T"}
text as b64 eyJudWwi OiJIUzI1 NiIsInR5 cCI6IkpX VCJ9
change bytes of {"alg" = {None BIG PROBLEM everything needs changing as 1bit was altered
text as txt {None: "HS256 ","typ ":"JWT "}
text as b64 e05vbmU6 IkhTMjU2 IiwidHlw IjoiSldU In0=
you MUST only change a block of 6x8 chars between boundary divisions for a new block of 8x6 chars between the same boundaries.
To make changes its best done in the related application thus for images use decode base64 to binary then use image editor and re encode back to base64. If you dont have the native fast base64 app as used on mac or linux then for poor window mans drag and drop (or commandline add filename) base64.cmd you can adapt:-
IF /I %~x1==.b64 goto Decode
rem todo IF /I %~x1==.hex goto HexDecode
FOR %%X in (.jpg .pdf .png) do IF /I %~x1==%%X goto Encode
:Help
echo Format unexpected, accepts .b64 .jpg .pdf OR .png
pause&exit /b
:Encode an accepted file to Base64 and trim off both -----BEGIN / END CERTIFICATE-----
Rem NOTE:- WILL overwrite, also previous .ext will be changed to lower case and .b64 appended
certutil -encode "%~pdn1%~x1" %temp%\tmp.b64 && findstr /v /c:-- %temp%\tmp.b64 > "%~pdn1%~x1.b64" && del %temp%\tmp.b64
Rem EXIT since we must not / cannot over-write the source
pause&exit /b
:Decode a .Base64 file to binary removing the appended .b64 NOTE:- will NOT allow overwite, thus error.
certutil -decode "%~pdn1.b64" "%~pdn1"
pause&exit /b