Is there a software wallet that lets me use a passphrase as a seed extension?

[d5000]

I recently came up with the following thought:

When I use a software HD wallet like Electrum with a passphrase, but a thief finds my seed, then the passphrase of course isn't necessary for him to simply steal my bitcoins. The passphrase only protects a wallet file, not the seed.

When I use the HD wallet with a seed extension instead (e.g. a 13th word) and store the seed and the seed extension separately, or remember the seed extension in my brain like I would do with the passphrase, then the thief can't access the coins just by knowing the "regular" seed. The extension does protect the seed (if I'm not stupidly storing them together, e.g. on the same paper). However, if he gets access to the device where I have the coins stored, then he will be able to move the coins, because the additional word(s) are simply stored in the wallet file and aren't asked when the wallet is opened.

So to avoid both security problems, I would have to set up both a "seed extension" and a passphrase. This are ideally two long and different (!) random passwords to remember or store separately.

However, if I could use the seed extension as the passphrase, I'd have almost the same level of security, but with only one word to remember.

(What I mean with that is that the seed extension is used to encrypt the wallet file, and is asked when I fire up the wallet.)

Does any software wallet software similar to Electrum offer that option? Would be really "nice to have", if there's nothing I'm missing ...


PS: I think I overthought here. If I simply use the seed extension as passphrase, this should in theory work and protect the wallet in the way I thought. For whatever reason I thought this would result in a situation where the security would be actually reduced regarding both using a passphrase and a seed extension ...

Wanted to delete the topic but it's not possible, so I leave this a couple of days to see if my thought in the PS was correct.

[Zaguru12]

PS: I think I overthought here. If I simply use the seed extension as passphrase, this should in theory work and protect the wallet in the way I thought. For whatever reason I thought this would result in a situation where the security would be actually reduced regarding both using a passphrase and a seed extension ...

Not going to lie I was actually thrown overboard my this question most especially since it is coming from you.

I have know a wallet passphrase to be seed extension which is you add extra word to the seed phrase (mnemonic seed) and this doesn’t only protects your file but must  be combine with seed phrase to steal your coin.

I think from what I read you are using the word passphrase here for the most common thing we know it for which is Password and it’s definitely different from passphrase or seed extension except maybe I have been wrong all this while.

So if your intention is to have both password and seed extension (passphrase) same i definitely think it’s possible with even your electrum or sparrow wallet or BlueWallet but I am concerned about the security because you basically have to enter this password any time you open the wallet and this can be revealed so I will say its best to different even if it’s a character

[nc50lc]

PS: I think I overthought here. If I simply use the seed extension as passphrase, this should in theory work and protect the wallet in the way I thought. For whatever reason I thought this would result in a situation where the security would be actually reduced regarding both using a passphrase and a seed extension ...

Are you pertaining to the "wallet encryption passphrase" when you've said "passphrase"?
Based from the context, it appears that you're talking about two different things by separating seed extension and passphrase.

Because most users tend to immediately link it to BIP39 passphrase (same to Electrum's "custom words") when they see that term, it may cause confusion.
Electrum on the other hand, uses the "Password" term for its wallet encryption.

[Charles-Tim]

When discussing about Electrum, what you use for encryption is the password, but if you extend the seed phrase with extra word, we referred to it as passphrase.

What you called the seed extension is called passphrase.

PS: I think I overthought here. If I simply use the seed extension as passphrase, this should in theory work and protect the wallet in the way I thought. For whatever reason I thought this would result in a situation where the security would be actually reduced regarding both using a passphrase and a seed extension

Yes, you are very correct.

I prefer to use a password that I know offhand on Electrum. I will remember the password as I use Electrum often, but if I forget it, I can recover my coins through the seed phrase and passphrase. I do not go for wallet file backup. But even if I go for wallet file backup, I will prefer to use different characters for it that is not the same as my passphrase/seed extension.

But if the same characters are used for both passphrase and for wallet file encryption, I do not think the security of the wallet is reduced at all because only one is needed to have access to your coins. So far the passphrase and the file encryption password is not on the device and protected somewere esle, the wallet security is not reduced.

[ABCbits]

Does any software wallet software similar to Electrum offer that option? Would be really "nice to have", if there's nothing I'm missing ...

Have you checked Wasabi Wallet? Here's the proof if needed.

Select Create a new wallet.

Now follow the next few steps/dialogs:

    Select the Wallet Backup Type.
    Write down the recovery words. (do not share these with anyone!)
    Add a passphrase. (do not forget it and also write it down on a separate place from the recovery words, without your passphrase you cannot open your wallet and send your bitcoin!)

But it's worth to mention the sync time can be long since the wallet use BIP 157/158, even if you run node locally and Wasabi Wallet connect to your node.

[cambio]

Your thought in the PS is spot on. You can simply use the exact same string as both your seed extension (passphrase) and your wallet file encryption password.

Electrum actually supports seed extensions during creation (under Options -> Extend this seed with custom words). Once the wallet is generated using that extension, it asks you to set a password to encrypt the local wallet file. Entering the exact same passphrase there achieves exactly what you want: you only have to memorize or securely store one secret phrase, the local file is encrypted with it, and someone finding just the 12 words on paper cannot access your funds without it.

Just keep in mind that unlike the wallet password, a seed extension has no "wrong password" check. If you make a typo when restoring from the seed, it generates an empty wallet without warning. Never share your seed or passphrase with anyone.