Dec 9: Sound Transmission

Challenge

Hear it, find it, brute it

sadly we didnt receive todays code transmission properly and it seems that a part of the information got lost. are you able to recover the missing parts?

all we know is that the lowercase sha1 of the code gives:

B39ECFBC2C64ADBB7C7A9292EEE31794D28FE224

and the sha1 of the case sensitive code should be:

0D353038908AD0FC8C51A5312BB3E2FEE1CDDF83

Solution

In the sound file we hear a voice saying the following letters, question marks indicate letters that were deliberatly left out.

HV?5-G?UJ-1YQ7-?DYC-2WLR-E6?J

That looks like almost a nugget. There are 4 unknown characters, of which we know the first one should be 1 to comply to the nugget format.

That leaves 3 unknowns, and we know what the sha1 hash of the lowercase version of the nugget should be. We can use that to find the 3 missing characters, and then we can try all the different casing of the string until we find the one that fits with the case-sensitive SHA1 hash. This sound like a very reasonable brute-force problem, so we write a small python script to solve it

import itertools
import hashlib

def all_casings(input_string):
    if not input_string:
        yield ""
    else:
        first = input_string[:1]
        if first.lower() == first.upper():
            for sub_casing in all_casings(input_string[1:]):
                yield first + sub_casing
        else:
            for sub_casing in all_casings(input_string[1:]):
                yield first.lower() + sub_casing
                yield first.upper() + sub_casing

target_lc='B39ECFBC2C64ADBB7C7A9292EEE31794D28FE224'.lower()
target_cs='0D353038908AD0FC8C51A5312BB3E2FEE1CDDF83'.lower()

charset='abcdefghijklmnopqrstuvwxyz0123456789'


for i in itertools.product(charset, repeat=3):
    nugget = 'hv15-g'+i[0]+'uj-1yq7-'+i[1]+'dyc-2wlr-e6'+i[2]+'j'
    h = hashlib.sha1()
    h.update(nugget)
    h_hex = h.hexdigest()
    if h_hex == target_lc:
        print 'Found lowercase match!'
        print ' --> nugget: '+ nugget +' (sha1 '+h.hexdigest()+')'
        break

print 'Searching for the correct case..'
for i in all_casings(nugget):
    h = hashlib.sha1()
    h.update(i)
    h_hex = h.hexdigest()
    if h_hex == target_cs:
        print 'Found case-sensitive match!'
        print ' --> nugget: '+ i + ' (sha1 '+h.hexdigest()+')'
        break

This outputs:

Found lowercase match!
 --> nugget: hv15-gnuj-1yq7-vdyc-2wlr-e6xj (sha1 b39ecfbc2c64adbb7c7a9292eee31794d28fe224)
Searching for the correct case..
Found case-sensitive match!
 --> nugget: HV15-GnUj-1YQ7-vdYC-2wlr-E6xj (sha1 0d353038908ad0fc8c51a5312bb3e2fee1cddf83)

Dec 9: Sound Transmission

Challenge

Solution

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