Click on the link and download the puTTY key generator.
https://www.puttygen.com/download-putty#PuTTY_for_windows
Open the downloaded file. Click next.
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Choose the destination folder.
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Click install. Permission will be asked. Click yes.
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After Installation click finish.
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Search puTTYgen in applications. Click Run as administrator.
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Click on Generate. Then move your cursor continuously for 2 seconds.
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The Key will be generated. Type the user-id and give any key passphrase [password]. Then copy the key which is generated.
NB: After key comment and pass phrase only you can copy the key.
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The Key is generated and copied.