If I lose wallet.dat can I recover it with the passphrase?

[99Percent]

My apologies if this has been asked before.

This regarding the standard bitcoin-qt client.

I havent lost my wallet file but I am curious to know just how important is it to back it up. I am thinking it might not even be necessary if I can restore it by just remembering the passphrase.

So, is it possible to recreate the private keys with just the passphrase?

[freewil]

If you're asking about the passphrase you used to encrypt your wallet.dat containing your private keys then the answer is no. You will still have lost all your private keys contained in wallet.dat - so it is useless to know the passphrase to decrypt the data which you no longer have.

If you're talking about a passphrase that you use to generate a private key as you would with a "brain wallet" then as long as you can remember the passphrase then you should be able to regenerate the private key.

[99Percent]

Thanks freewill

I am talking about the passphrase the bitcoin-qt clients asks whenever I want to send bitcoins or create a new receiving address.

If this is not the on for generating a "brain wallet", how can I proceed to create one?

[CIYAM]

I am talking about the passphrase the bitcoin-qt clients asks whenever I want to send bitcoins or create a new receiving address.

If this is not the on for generating a "brain wallet", how can I proceed to create one?

The standard client cannot generate a "deterministic wallet" (the term "brain wallet" generally refers to the generation of a single address via SHA256 of a long pass phrase whereas "deterministic wallet" refers to using a seed and pass phrase to generate a series of addresses).

If you are keen to create such a wallet then you should look into using Armory or Electrum.