A tough nut
Over here, the bold letters when entered into a ROT13 cipher give the key that that is used for decrypting the vigenere cipher encrypted with that key.
A python script to do the job.
#!/usr/bin/python3
from string import ascii_letters
def vigenere_decode(key, encryption):
decrypt = ""
key = key.lower()
encryption = encryption.lower()
for i in range(len(encryption)):
if encryption[i] in ascii_letters:
decrypt += chr(
(ord(encryption[i]) - ord(key[i % len(key)])) % 26 + ord("a")
)
else:
decrypt += encryption[i]
return decrypt
print(vigenere_decode("lemon", "LXFOPVEFRNHR"))