Amazon EC2 uses public-key cryptography to encrypt and decrypt login information. Public–key cryptography uses a public key to encrypt a piece of data, such as a password, then you use the private key to decrypt the data. The public and private key combination is known as a key pair.
To log on to your instance, you must create a key pair, specify the name of the key pair when you launch the instance, and provide the private key when you connect to the instance. Linux instances have no password, and you use a key pair to log on using SSH.
If you create a key pair in one region, you cannot see or use that key pair in another region. In other words, key pairs cannot be shared between regions. You can create your own key pair that you can use in all regions by using a third-party tool and then importing the key to Amazon EC2.
For more information on key pairs, see Amazon User Guide for Linux Instances.