The prime-generation method does not affect compatibility: a key generated with any of these methods will still work with all the same SSH servers. (The other key types don’t require generating prime numbers at all.) On the Key menu, you can also optionally change the method for generating the prime numbers used in the generated key. (256 is also accepted for backward compatibility, but the effect is the same as 255.) For EdDSA, the only valid sizes are 255 bits (these keys are also known as Ed25519 and are commonly used) and 448 bits (Ed448, which is much less common at the time of writing).(ECDSA offers equivalent security to RSA with smaller key sizes.) For ECDSA, only 256, 384, and 521 bits are supported.For RSA and DSA, 2048 bits should currently be sufficient for most purposes.
The Number of bits input box allows you to choose the strength of the key PuTTYgen will generate. But SSH-1 is no longer supported by WinSCP. PuTTYgen can also generate an RSA key suitable for use with the deprecated SSH-1 protocol (which only supports RSA).
Then press the Generate button, to actually generate the key.First, you need to select which type of key you want to generate, and also select the strength of the key.The following sections describe the process in more detail. This is a general outline of the procedure for generating a new key pair. When you run PuTTYgen you will see a window where you have two main choices: Generate, to generate a new public/private key pair, or Load to load in an existing private key. To start PuTTYgen, go to Tools > PuTTYgen on Login dialog. It does not matter if you use PuTTYgen from WinSCP or the PuTTY installation package, they are identical. PuTTYgen originates from PuTTY and is also part of the PuTTY installation package.