what is the best software based solution to secure the private key in Bitcoin Would you mind telling me what is the best introduced approach to secure the private key in the wallet and a transaction which is done using Bitcoin? I do not want to use a separate hardware, I am seeking for the best software based approach to protect the private key. 

Thanks in advance

Best Regards
Hm. Rather strange question you ask.

First of all: it depends mostly on the infrastructure you use for your bitcoin-client.

If your OperatingSystem is compromised, you probably can't guarantee security of your privateKey at all. 

The Bitcoinclient supports a very strong encryption of the wallet (and ofc the private Key) since like 2 years natively. 

I guess if you are paranoid and want extra security, use a VirtualMachine, install some hardened Linux-OS (DebianStable?), there make a TrueCrypt-Container with a hard password and install your Bitcoinclient there.

Ofcourse, as mentioned earlier, you can't be more secure than making an offline-wallet. Remebering your key instead of writing it down could also serve as the absolute security feature. - but i guess you don't want to go that far? :)

i saved my keys in a TrueCryp-container encrypted with sha512 and used a strong password - after this, backup copies of this container wherever you want, so you don't lose it. sha512 is not even crackable for the NSA.