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- Now let's talk about key
pairs within Amazon EC2.

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Key pairs, or public private keys

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are the way in which we can authenticate

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into the operating system
of our EC2 instances.

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You remember when we talked earlier

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about authenticating against the AWS API,

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we use a certain set of
access keys for that,

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using IM users and groups.

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What we're talking about here

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is the OS level of authentication.

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Here, in order to get
into the operating system,

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or EC2 instance, we need a key pair.

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Now, these are 2048-bit
SSH-2 RSA key pairs.

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We will create these
within the AWS console,

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and then when we go to
launch an EC2 instance,

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we will choose that key pair at that time.

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Now, when we create the key pair,

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Amazon web services will
keep the public key.

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They will give us the opportunity

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to download the private
key, and then at that point,

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they will not longer keep the private key.

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So you do have one short
window in which to download

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the private key before
Amazon gets rid of it.

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How this works is that when we
launch a Linux EC2 instance,

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Amazon web services will
take that public key

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that they're keeping, and
they will add it to the

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.ssh/authorized_keys files for
your particular admin user.

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Like in the case of Ubuntu,

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they will add it to the Ubunto user.

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In the case of Amazon Linux,
they will add it to the,

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what we call the EC2 user.

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And we will use it, when we go to log in

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our SSH into that Linux machine,

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we will use our private
key that we downloaded

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in order to authenticate
against that operating system.

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In the case of Windows,
the administrator password

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will be encrypted using the public key,

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and we will use our private key to decrypt

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the Windows administrator password.

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So again, key pairs are the way in which

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we authenticate into the operating system

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of Amazon Elastic Compute Cloud instances.