import streamlit as st
import hashlib
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import (
   padding, rsa, utils
)
private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=2048,
)

st.write("""
## Tanda Tangan Digital RSA
""") 
input = st.text_input('Masukkan Teks', 'Niko Irsyad')

prehashed_msg = hashlib.sha256(input.encode()).digest()
signature = private_key.sign(
    prehashed_msg,
    padding.PSS(
        mgf=padding.MGF1(hashes.SHA256()),
        salt_length=padding.PSS.MAX_LENGTH
    ),
    utils.Prehashed(hashes.SHA256())
)

st.write("Tanda tangan digital :", signature)

public_key = private_key.public_key()

try :
    public_key.verify(
        signature,
        prehashed_msg,
        padding.PSS(
            mgf=padding.MGF1(hashes.SHA256()),
            salt_length=padding.PSS.MAX_LENGTH
        ),
        utils.Prehashed(hashes.SHA256())
    )
    st.write('Tanda tangan VALID')
except InvalidSignature:
    st.write('Tanda tangan INVALID')