Is there any x for which SHA1(x) equals x?

Is there an x where SHA1(x) == x? I'm looking for a proof o开发者_运维百科r a strong argument against it.

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The same arguments apply here as for the question Is there an MD5 fixed point? I.e. for a randomly chosen function it is about 63%.

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Read about fixed point attack on this wiki entry One-way compression function - Davies-Meyer

Most widely used hash functions, including MD5, SHA-1 and SHA-2
use Merkle-Damgård construction.