How can I convert my private key from bitaddress.org to WIF without putting the key into a website or a programme?
bitaddress.org already provides your private key in Wallet Import Format, which is encoded in base58check format.
In the example screenshot below, the base58check-encoded WIF private key is KzNKqwBPaVehsA2F94n9UJ5mrkM9NazBjqBBwsb2U9pAGLdc4md3
To address your &quot;rule 1&quot;, the most secure way to handle this data is load Electrum onto an airgapped machine, enter the private key into that secure computer, and then use it to sign a transaction you build with an &quot;online&quot; machine that has access to the UTXO set and your wallet address.

Warning: Do not use the key or address in this example for any reason at all besides looking at it and learning! Pasting private keys on websites is always a terrible idea.