PuTTY does not natively support the private key format (.pem) generated by Amazon EC2. If you load the .pem formet private key directly to PuTTY you will get error message: Unable to use key file “***.pem” (OpenSSH SSH-2 private key). PuTTY has a tool called PuTTYgen, which can convert keys to the required PuTTY format (.ppk). You must convert your private key into this format (.ppk) before connecting to your instance using PuTTY.

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