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- Encryption has been part

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of signals intelligence
for quite some time.

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Caesar cipher,

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Vigenère cipher, ROT-13, et cetera.

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If there's a secret you want protected,

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encrypt it.

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One-way hashing is not encryption

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but it is used to protect passwords.

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While not reversible, hashing algorithms

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were designed to be computed quickly.

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So you can compute many
hashes from a dynamic source

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like a word list or
permutations, brute force

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and compare the results to find a match.

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Let's take a look at how hashing works.

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We first start with
cleartext like pearson.

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We send it through a hash function,

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in this case, we're using MD5.

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As the hash function applies

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a one-way hashing algorithm,

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the output of the function is a string

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of characters that is unique

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to that specific cleartext that we input.

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Now this string can be used

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in different ways to verify the integrity

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of cleartext that was provided.

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For instance,

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if a cleartext email is sent through

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a hash function

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by the sender

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and the hash was provided to the recipient

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they can use it to verify

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that the email was not changed in transit.

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So in this demo, I want to
just show you a really quick

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and easy way to generate
a hash of cleartext

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just like we did in the previous slides.

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Of course, we're not gonna use MD5

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because today

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we have better algorithms for hashing,

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like SHA-256.

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So what I'm gonna show you here is

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how to do this from the
colleague command line.

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What you would do is type echo,

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then type in your cleartext

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and simply pipe it over to
the SHA-256 sum command.

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And we can see here,

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it spits out a long set of characters.

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That's our hash of the
cleartext word pearson.

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If we run it again, we
see it's the same hash.

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This is the way that a
hashing algorithm works.

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It should always be the
same unless it was modified.

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So if we were to say,

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add a one to pearson,
run it through again,

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the hash should change.

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As you can imagine, this
is how hashing can be used

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for things like email
integrity validation.