How do I store keypair in s3? - amazon-s3

Question

I referred this stackoverflow answer:
ssh key of newly created ec2 instance using boto
where if the keypair doesn't exist, it creates a new one and saves the private keypair.
However, I wish to save the keypair in s3 or some common place between mac and windows users. I know the directory hierarchy is different for both OS so how do I hard code a value that works for both?
My current code:
# Check to see if specified keypair already exists.
# If we get an InvalidKeyPair.NotFound error back from EC2,
# it means that it doesn't exist and we need to create it.
try:
key = ec2.get_all_key_pairs(keynames=[keypair_name])[0]
except ec2.ResponseError, e:
if e.code == 'InvalidKeyPair.NotFound':
print 'Creating keypair: %s' % keypair_name
# Create an SSH key to use when logging into instances.
key = ec2.create_key_pair(keypair_name)
key.save('https://s3.amazonaws.com/' + bucket_name)
else:
raise
The key.save line makes the url something like "https://s3.amazonaws.com/bucket_name\launch.pem"

Answer 1

The boto.ec2.keypair.KeyPair object's .save function saves the material (the unencrypted PEM encoded RSA private key) of a newly created KeyPair to a local file.
It is invalid syntax to use key.save('https://s3.amazonaws.com/' + bucket_name). Amazon S3 is not a local filesystem.
To store the file on S3, first download it to the local computer, then upload it via the S3 API calls.
It's worth mentioning that EC2 Key Pairs are provided for initial access to EC2 instances. Once you login to an instance, you should implement your own security for the instance, such as creating users and adding your own keypairs, or connecting to an LDAP or Active Directory server.