List strings which may appear when a target string is base 64-encoded

improved_single_reverse_base64.py

#!/usr/bin/python
import base64
import sys
input = sys.argv[1]

drop = [0, 2, 3]

def get_combinations(s):
 return [(base64.urlsafe_b64encode('a'*i + s)[drop[i]:]).replace('=', '') for i in range(3)]

for x in [get_combinations(sys.argv[1])]:
 for y in x:
  print(y)

single_reverse_base64.py

#!/usr/bin/python
import base64
import sys
input = sys.argv[1]

def get_combinations(s):
 return [base64.urlsafe_b64encode('a'*i + s)[2*i:-4] for i in range(3)]

for x in [get_combinations(sys.argv[1])]:
 for y in x:
  print(y)

Sample usage:

# Setup: encode "elastic mapreduce" and write it to a file
echo "elastic mapreduce" | base64 > encoded.txt

# search the file for any of a list of strings to which "mapreduce" might be encoded
grep -f <(./single_reverse_base64.py mapreduce) encoded.txt