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One Time Pad

Tinker tailor tourist spy › Forums › Bureau of Security and Signals Intelligence Forum › One Time Pad

Viewing 15 posts - 1 through 15 (of 23 total)
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  • 12th January 2021 at 3:29 pm #52887
    67105112104101114
    Participant

    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

    15th January 2021 at 12:03 pm #52985
    Kford-academy
    Participant

    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

    16th January 2021 at 4:41 pm #53001
    67105112104101114
    Participant

    Congrats @Kford-academy on cracking the cipher

    16th January 2021 at 7:19 pm #53003
    Madness
    Participant

    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

    19th January 2021 at 12:47 pm #53034
    F6exb
    Participant

    #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?

    19th January 2021 at 2:05 pm #53035
    67105112104101114
    Participant

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

    19th January 2021 at 2:32 pm #53040
    F6exb
    Participant

    Tnx I got it 😉

    PLAINTEXTF6EXB: 6adacd6e9a4fde728f1bf8a5cfda3a7b

    20th January 2021 at 9:39 am #53051
    Mattyrat2027
    Participant

    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.

    20th January 2021 at 2:45 pm #53061
    The-letter-wriggler
    Participant

    A little late getting around to doing this one!

    PLAINTEXT+TLW MD: 51360e5d5ef835f98d83e50d0616dd70

    20th January 2021 at 3:41 pm #53062
    Mattyrat2027
    Participant

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

    20th January 2021 at 10:42 pm #53066
    Pandarran
    Participant

    Thanks for the challenge!

    MD5 of PLAINTEXTPANDARRAN is 20a84a1f92e9725c669b7560ed7661d4

    21st January 2021 at 1:23 pm #53086
    Philthy
    Participant

    Thanks, @67105112104101114
    md5 of PLAINTEXTPHILTHY is bef78092d5e5c1baa41392bde6229bbc


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

    21st January 2021 at 2:14 pm #53087
    Madness
    Participant

    @Philthy, guesswork?

    21st January 2021 at 7:06 pm #53090
    Tsyzygy
    Participant

    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!

    21st January 2021 at 7:07 pm #53082
    Mattyrat2027
    Participant

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

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