How to extract public key using OpenSSL?

The following command generates a file which contains both public and private key:

openssl genrsa -des3 -out privkey.pem 2048

Source: http://www.openssl.org/docs/HOWTO/keys.txt">here</a>

With OpenSSL, the private key contains the public key information as well, so a public key doesn't need to be generated separately

How can we extract the public key from the privkey.pem file?

Thanks.

openssl rsa -in privkey.pem -pubout > key.pub

That writes the public key to key.pub

Though, the above technique works for the general case, it didn't work on Amazon Web Services (AWS) PEM files.

I did find in the AWS docs the following command works: ssh-keygen -y

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html

edit Thanks @makenova for the complete line:

ssh-keygen -y -f key.pem > key.pub

For those interested in the details - you can see what's inside the public key file (generated as explained above), by doing this:-

openssl rsa -noout -text -inform PEM -in key.pub -pubin

or for the private key file, this:-

openssl rsa -noout -text -in key.private

which outputs as text on the console the actual components of the key (modulus, exponents, primes, ...)

For AWS importing an existing public key,

1. Export from the .pem doing this... (on linux)

    openssl rsa -in ./AWSGeneratedKey.pem -pubout -out PublicKey.pub
   

This will produce a file which if you open in a text editor looking something like this...

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAn/8y3uYCQxSXZ58OYceG
A4uPdGHZXDYOQR11xcHTrH13jJEzdkYZG8irtyG+m3Jb6f9F8WkmTZxl+4YtkJdN
9WyrKhxq4Vbt42BthadX3Ty/pKkJ81Qn8KjxWoL+SMaCGFzRlfWsFju9Q5C7+aTj
eEKyFujH5bUTGX87nULRfg67tmtxBlT8WWWtFe2O/wedBTGGQxXMpwh4ObjLl3Qh
bfwxlBbh2N4471TyrErv04lbNecGaQqYxGrY8Ot3l2V2fXCzghAQg26Hc4dR2wyA
PPgWq78db+gU3QsePeo2Ki5sonkcyQQQlCkL35Asbv8khvk90gist4kijPnVBCuv
cwIDAQAB
-----END PUBLIC KEY-----

2. However AWS will NOT accept this file.

You have to strip off the `-----BEGIN PUBLIC KEY-----` and `-----END PUBLIC KEY-----` from the file. Save it and import and it should work in AWS.

If your looking how to copy an Amazon AWS .pem keypair into a different region do the following:

openssl rsa -in .ssh/amazon-aws.pem -pubout > .ssh/amazon-aws.pub

Then

aws ec2 import-key-pair --key-name amazon-aws --public-key-material '$(cat .ssh/amazon-aws.pub)' --region us-west-2

use openssl to extract the pub file from the pem file as

openssl x509 -inform pem -in private_key.pem -pubkey -noout > public_key.pub