MatthieuLemoine

const id         = '__JUNK__';
// Public key need to be in PKCS8 format
// ssh-keygen -e -m PKCS8 -f id_rsa.pub > id_rsa.pkcs8
const publicKey  = fs.readFileSync(path.join(__dirname, 'id_rsa.pkcs8'), { encoding : 'utf8' });
const privateKey = fs.readFileSync(path.join(__dirname, 'id_rsa'), { encoding : 'utf8' });

// Sign
const signer = crypto.createSign('RSA-SHA512');
signer.update(id);
const signature = signer.sign(privateKey, 'hex');