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Here are some details:

I was given was a text that was

  1. converted into hexadecimal, then
  2. hashed via MD5, then
  3. hashed via SHA-1.

That’s all I know about it.

Any help is really appreciated. There is a large bet on this. Is it even possible or is it totally impossible?

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  • $\begingroup$ How large is the bet? For $1M USD, I'll find the answer for you :) P.S., if you are trying to reverse the hashes, you are doing it wrong. Instead, you'd have to do a dictionary attack and go the forward direction. If the original text was long enough and has enough entropy, it will be impossible. $\endgroup$ – mikeazo May 22 '17 at 17:18
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Although there already is a successful second pre-image collision attack on SHA-1, it took a lot of time. And there is no known information about successful reversing SHA-1. So you would need years (or decades) to accomplish that mission.

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    $\begingroup$ Assuming current computational power and cryptographic knowledge, your "years (or decades)" are really closer to a few trillion years. $\endgroup$ – yyyyyyy May 21 '17 at 10:19
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    $\begingroup$ Note: This is not a second pre-image attack. What was accomplished is a collision attack. A second pre-image attack would require to find (for a given $x$) an $x'$ such that $x\neq x'$ but $H(x)=H(x')$. This has not been done and it there's no known (?) way to do this with less than $2^{160}$ effort. This means that $x$ is given to you, whereas in a collision attack you are allowed to pick $x$ yourself. $\endgroup$ – SEJPM May 21 '17 at 14:07
  • $\begingroup$ Note also that - since you cannot reverse SHA-1- that you cannot find the output of the MD5 hash. That means that any attacks regarding the reversal of the MD5 hash are unavailable. Not that this would help much, as the much stronger attacks on MD5 still require similar conditions as the SHA-1 attack. So you're left with guessing the input. $\endgroup$ – Maarten - reinstate Monica May 21 '17 at 15:40

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