One Time Pad

[67105112104101114]

The one-time pad is a cipher which is completely uncrackable due to its use of a key as long as the message that is being transmitted however it has the issue of needing both people to already have the key without it having fallen in enemy hands to work. The challenge is to crack this message which is known to have been encrypted with a OTP:
JSEUNNFCYDTAKRDZNUJHGMWHRWMSJXJSUROHRWEEFVLXDJWWLBIVLUCCTICDJLLAUIPHKYIMPGRESCJYGRS
WBEPQQCSXUKRZHQUFLBSBTKSMERTLKKKAHMHGBGVYSTWCSRCLXKHXYXFCHDXNOCFKBAGRRZWKXDU
However, luckily because this would be impossible without it, we have also intercepted the message sent before it by the same person and got hold of the plaintext used to create that message:
TSQUMOOMSJOZFGDRXRIRXKVWVAKMKQHGXSOXTVQZICYIZKITLSCIGXSCOOJKYGKOYAHDAJUHZWLDRXUSOSO
XGHHFMDMGRWTCHNGPWMIMVVGZCBUKUCPOSIRCMVMLVJILZWPHZSKDNEGLLCXESQMETOJIAHZUOBIIKAMXXO
QOMJQELSRHSOPBZBZQYKWOLEXWHRMOSORAKATURSNBTUHCGUWTFUKMGBTQAVIKZFAGWHUWJCFLXEMWROQUW
PMEOFUWA

THISISOURFIRSTVERYULTRASECRETMESSAGEANDTHEREISABSOLUTELYNOWAYTHATTHISWOULDEVERBELEA
KEDTOTHEENEMYANDASITISNTGOINGTOBELEAKEDTHENITISPERFECTLYSECUREBECAUSEITISAONETIMEPA
DWEWILLFOLLOWTHISMESSAGEWITHTHEULTRAIMPORTANTINFORMATIONCOMINGINANOTHERONETIMEPADCO
MINGSOON
The challenge is to use this information to crack the other message

[Kford-academy]

Thanks, @67105112104101114! Here is my message to you, encrypted with the same key as the second message (the one we were meant to crack):
ALRBGFULRIIFEXPWYWFQSASXEUDWEZASMWGGTFQBRSRAYNGLHVWLQWOXSTLCEBHMSDCUILWLHKVL

[67105112104101114]

Congrats @Kford-academy on cracking the cipher

[Madness]

These two ciphertexts were encrypted with the same key, not two parts of the same key text as in the first
post in this thread. Exactly the same key. Can you now break them? This is why you should never re-use
the key from a one-time pad; two-time pads are insecure.

PPHKLXETAGOTLJGODXRODJBSJQGYGXJLGTKSGPHBTFEJSDXKEESUWLDDPVCVPKPZQMGFAEFTQLUKSBEJLHHHSKZFXNOY
IDGMQOICSMZQQIUFYQBGCEZXVDJTBOGTXDRPWRIDTORXABUGDGIRGGBYHYRIRIJEKTLOMKIMKERZHFGZVCMOORRAMIHI
RERZCPLCYFJKWPQRSHKTQIHBAYZXLBZOUJZRXNYBGIEVWJUXBSTOGWABQHGHPUCRISHTSTHDCCRAWABIZPEOWQVOBJYY
SCNUUPYUFOVBZAOSCSODBKWGWRRVUQQRHDVHTJYSLGZRHWAKWYWTNPITYMPCQSRUKAHSJLKCZYEIDOEDVAHFIQGHNYOD
MLOTWANYAGXIHUVSNMGVLKYHBJTNUSVFFAFNKNMBMZPCN

HRETWPKMQUJEBMKEIMIKXNEEMHOZIETHUNQFKTKWPERUSDTRDTWJIARUGMOSLDCRFTHPMOJTRHWDEIYUKUCQNRFGRJDG
FOABXJCMPNRPBUUPRHMKXOGFCFJEJFWPKGRPMGPGCKHBTFPVUPIIKBQSBFEJQQCENZWDUWIXUOVXSMMVACYCYRWCAQOG
ICTCKWXJGIVPVQQUNYXJBMHDIIXDLYJQRTGECARZHPPCHMFDRCUPJHIXDRXNPRUDQGVRPDQTVEEFBZVNNZEPCURLANGY
FOPVUBLRPVAEUMJZHAUDAKQUBHLKBSFLEGYJCFDSXDCXHUULMIAWDJXESREIEWQCGECWCFLGMMEDTXFCMSFSDWTSZWAX
CIZEJIJANPAWLWTFMCAEBKMZFUUYVPVAPPDCPTLVXOMROVANDAUH

[F6exb]

#52887
Hello,
I have recovered the key with Excel, but can’t decipher the first ciphertext:
I tried to shift the ciphertext along the key one letter after one letter down to the end of the key, tried also with the reversed key.
Any hint please?

[67105112104101114]

The two ciphers could have been encrypted as one block of text, try reading the key @F6exb

[F6exb]

Tnx I got it 😉

PLAINTEXTF6EXB: 6adacd6e9a4fde728f1bf8a5cfda3a7b

[Mattyrat2027]

I don’t know if this will be permitted but I came across a clear weakness when I knew about the key:

If you know the ciphertext and are trying to decrypt it into the plaintext to recover the key (as we did thanks to #52887), then you can type the next letter of the plaintext on the end of the key, and the letter that appears on the decryption will be the letter of the key to decipher the ciphertext correctly.

I hope you understand that, if it is allowed, and you may be able to use it to your advantage.

[The-letter-wriggler]

A little late getting around to doing this one!

PLAINTEXT+TLW MD: 51360e5d5ef835f98d83e50d0616dd70

[Mattyrat2027]

I love the choice of key…um…paragraph? PLAINTEXTMATTYRAT2027 – 4c4eaae87e00d49dcf7a7da91fc67e30
I might have to create one myself!

[Pandarran]

Thanks for the challenge!

MD5 of PLAINTEXTPANDARRAN is 20a84a1f92e9725c669b7560ed7661d4

[Philthy]

Thanks, @67105112104101114
md5 of PLAINTEXTPHILTHY is bef78092d5e5c1baa41392bde6229bbc

@Madness, any clues on how to break your 2 time pad challenge?

[Madness]

@Philthy, guesswork?

[Tsyzygy]

Nice challenge! md5 of PLAINTEXTTSYZYGY (all caps): 53993c9ca9bfa53e5de4264eda5d542e

Now for Madness’ challenge… I’m thinking genetic algorithm but perhaps that’s excessive. Time to find out!

[Mattyrat2027]

@Madness Is the key randomly generated? Might help me because my XOR method isn’t working

[Author]

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