Show key being used by 'multi_byte_xor'

[vdun]

Sample file: https://github.com/ctfs/write-ups-2017/raw/master/alexctf-2017/cryptography/cr2-many-time-secrets-100/msg

# featherduster /tmp/msg
FeatherDuster> analyze
[+] Analyzing samples...
[+] Messages appear to be ASCII hex encoded, hex decoding and analyzing again.
[+] Messages may be encrypted with a stream cipher or simple XOR.
[!] Individual messages have failed statistical tests for randomness.
[!] This suggests weak crypto is in use.
[!] Consider running single-byte or multi-byte XOR solvers.

[+] Suggested modules:
   alpha_shift          - A brute force attack against an alphabetic shift cipher.
   base_n_solver        - A solver for silly base-N encoding obfuscation.
   single_byte_xor      - A brute force attack against single-byte XOR encrypted ciphertext.
   multi_byte_xor       - A brute force attack against multi-byte XOR encrypted ciphertext.
   many_time_pad        - A statistical attack against keystream reuse in various stream ciphers.
   vigenere             - A module to break vigenere ciphers using index of coincidence for key length detection and frequency analysis.

FeatherDuster> use multi_byte_xor
FeatherDuster> run
[+] Running multi-byte XOR brute force attack...

Best candidate decryptions for )$*c4-+6i',  !...:
----------------------------------------

Trying keysize 26
Processing chunk 26 of 51
Trying keysize 13
Processing chunk 39 of 51
Trying keysize 12
Processing chunk 51 of 51
Dear Friend, This time I understood my mistake and used One time pad encryption scheme, I heard that it is the only encryption method that is mathematically proven to be not cracked ever if the key is kept secure, Let Me know if you agree with me to use this encryption scheme always.
Bfay<Friens0This tgSr.I uhgeyotood zemistakkv`d uufd+Sne tizypad enmLn~tioh#shteme, ^<Jeard tf_c.it op te onln<GncryptgQy.metnld+hhat id<OathemazWtolly&srdjen to7~G not c|_teed cuey<if thr<Iey is e[gz seevrn0 Let Zyknow ihnau aaqen<with zyto use.Jgs eh`rrltion dJeme aly_n}.
Wlao Ww[hes,-Vbic:chmt.I+MjmcosilZi my:oesdwzc {wd<Mqlb1Itfnize<rmh6tnec~tsWl%sunty[! X tkkyr:rean(inmq iyt#Qelh,girxjedit(ayGlfs=rydJ+ed+wcihswvyouogpA3yrrvtkyd7bh"dod:tsareeoaco teyhe qgu ye1mejm o]a|tt*:O[n Ze<ibca1xk7cau:Yewes&f}Je |e<ze+cic-tras:QjardaejQe borlge!{}zgc{"

How to show the key being used?

[unicornsasfuel]

It should be possible to modify cryptanalib.break_multi_byte_xor to show the key used to get some particular result.

If you really need the result now (CTF or some such) you can XOR the ciphertext and the result together with cryptanalib.sxor and you'll get the keystream.