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    Cryptography Private Key Extraction from Qualcomm Hardware-backed Keystores

    April 25, 2019

    Cryptography Private Key Extraction from Qualcomm Hardware-backed Keystores

    Private Key Extraction from Qualcomm Hardware-backed Keystores

    Posted: 24 Apr 2019 06:31 PM PDT

    A Crash Course in Everything Cryptographic

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    Posted: 25 Apr 2019 01:43 AM PDT

    iShook on Twitter

    Posted: 25 Apr 2019 01:43 AM PDT

    Crypto CTF woes

    Posted: 24 Apr 2019 04:46 PM PDT

    Hello,

    I recently tried a crypto CTF challenge, and I am stuck and it is boggling my mind!

    To win the challenge you need to retrieve a flag. To do that you have access to

    • An RSA encryption oracle. This oracle is needed because the modulus and the public exponent are not known. For this oracle you provide value x, and you get xe mod n back.
    • an oracle that you give a value i and you get i % φ(n) back.
    • The value of (e*f)e mod n, where f is the flag value

    Now i was able to retrieve n and φ(n). I could also factor n with this information. But then I am stuck. I can't think of a way to find e. My though process:

    • If e is a random number, then finding it would be solving the discrete log problem.
    • I tried values for e of the form 2m + 1 but they didnt work.
    • I tried just bruteforcing e in case it was small enough.
    • I tried bruteforcing d instead.

    One last thing: the value of n was about 1024 bits long if this makes a difference. I don't think this is bruteforcable in general, is it?

    Can anybody think of something? bonus points if you just give me a hint instead of the solution. Thanks!

    submitted by /u/catragore
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