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Can SHA 256 be modified to make it vulnerable to length extension attack both by appending text to the front and adding text to the end?

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    $\begingroup$ Without restriction on "modified", the answer is obviously yes. Hint for a surreptitious modification: that's possible with only a change in the 256-bit IV constant, and one of the reason to use a nothing up my sleeves number there. $\endgroup$ – fgrieu Aug 9 '18 at 2:12
  • $\begingroup$ That last part of your question is unclear. Do you need to be able to add "text" to the front in addition to the normal length extension attack that adds text to the end? Or do you need to be able to prepend and append at the same time? $\endgroup$ – Maarten Bodewes Aug 11 '18 at 9:23

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