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I am learning Hash Algorithms and in a presentation (PDF) about these algorithms I read that:

Length of $h(m)$ much shorter then length of $m$.

Now my question is:
What if we talk about an empty string, is it true that hash length is shorter than the length of message?

I searched the internet and found that:

The MD5 Hash of an empty string is:d41d8cd98f00b204e9800998ecf8427e

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up vote 6 down vote accepted

The presentation probably went along with a more verbose lecture.

I would assume there was some discussion about message lengths there, since that statement is obviously incorrect. In most applications, the "message" length is longer than the digest, and the average message length is also most likely longer. Think file verification, or processing of an actually message, instead of of a password.

In that statement, substitute "much shorter" to "usually much shorter"

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Thanks for your fast answer, it helped me a lot :) – Ultimo_m Jun 26 '14 at 19:06

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