Simple Cipher  - Cryptography Challenge 

For this challenge we’re given the following string to decode:

ebg kvvv vf n fvzcyr yrggre fhofgvghgvba pvcure gung
ercynprf n yrggre jvgu gur yrggre kvvv yrggref nsgre vg va gur
nycunorg. ebg kvvvvf narknzcyr bs gur pnrfne pvcure,
qrirybcrq va napvrag ebzr. synt vf synt_fjmtkowfnzdjkknh.
vafreg na haqrefpber vzzrqvngryl nsgre synt.

After some research, it seems that the string is encrypted using Caesar Cipher.

The question now is to know how much is the shift, knowing that there are 26 letters in the alphabet, so I coded a little script that will help me to test all the possibilities.

cipherText = 'ebg kvvv vf n fvzcyr yrggre fhofgvghgvba pvcure gung ercynprf n yrggre jvgu gur yrggre kvvv yrggref nsgre vg va gur nycunorg. ebg kvvvvf narknzcyr bs gur pnrfne pvcure, qrirybcrq va napvrag ebzr. synt vf synt_fjmtkowfnzdjkknh. vafreg na haqrefpber vzzrqvngryl nsgre synt.'

specialCharsList = ['.','_']

for i in range(26):
  results = ''
  for letter in cipherText:
    if letter.isspace() == True: 
      results += letter
    if letter in specialCharsList:
      results += letter
    results += chr((ord(letter) - ord('a') + i) % 26 + ord('a'))
  print('{}: {}\n'.format(i, results))

After running the script, it seems that with a shift of 13 characters I got a readable text. Once the right spaces are put in the right place the flag appear.

flag_lswzgxbjsamqwxxau