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I was just reading a bit on reddit. People are telling each other that legacy wallets are not secure anymore. Not that they have shown any proof on it, but is there any truth to this? I am wondering because I am asking for a friend, who has always used a legacy wallet in the paper form. He hasnt lost any coins, yet. But should he be worried about super computers cracking private keys?

A general purpose and stable high qubit quantum computer (which doesn't exist and no one is sure if will ever exist) can run an algorithm called shor's. Shor's is used to factor numbers. You can thus use shor's to derive a private key from a public key. Bitcoin exposes public keys in the scenarios of certain address reuse and when certain transactions are sitting in the mempool, as well as very old 2009 era pay to pubkey coinbases and new taproot transactions. What will happen if such a computer ever exists is slowly attempts to mine the most static of these coins, probably the old coinbases, will occur. Once this happens everyone will know there is a quantum actor and avoid address reuse or in the worst case just move to a new address format. It's also important to remember that a quantum attack takes considerable time, not dissimilar to mining, as it's the process for searching for a private key. Another Algorithm, called grovers, will enable a new kind of mining ASIC, similar to how generations of PoW devices have always functioned.

https://arxiv.org/abs/2410.04956

29 bit integer broken

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Send to your friend this guide https://darth-coin.github.io/wallets/move-btc-taproot-address-en.html

Legacy addresses are trash now. Also if you had legacy addresses and didn't reclaim your BCH and dump it for more BTC, then you were a loser, not doubling your stash.

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Darth, thank you for your update. I was wanting to hear from you. You are right, my friend should have changed his BCH to BTC, but he didnt want to move it from the address he already had. He wasnt willing to compromise his security for petty change. I will tell him that you think legacy addresses are trash, though.

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related to #721468 ?

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It could be. A lot of things relate to it.

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No, legacy wallets are fine. What’s more important is which software he used to generate his keys. If it was Bitcoin-QT/Bitcoin Core he’s fine

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I like your way of thinking!

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You’re on a roll. Two posts in two days

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I only post what I like. Im not really posting to make sats. Different objectives haha

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I haven't heard anything about this. It certainly sounds like FUD.

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That is what I am thinking, but it never hurts to ask the community experts.

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It's not FUD. You should upgrade from insecure addresses to modern adresses. Just like you should update your operating system to the newest version to fix security holes.

It's unfortunate but we should have never sold this idea of "forever" addresses. Idk where this idea came from in the first place, certainly not from people with a cs degree.

Even for the most optimistic people: it's foolish to think that cryptography from 20y ago is insecure but current cryptography will still be secure in 50y. Given history that would be a surprising future.

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I think it is a bit of both. Updating doesnt always make it more secure.

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What do you mean by "legacy wallets"?

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Old wallets that use addresses that begin with the number 1.

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Wallets that start with the number 1?

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An address is not the same as a wallet.

A wallet could have millions of address.

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You are right, and address that starts with the number 1.

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Not true. The 1 stands for #1 as in they're the best!

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Addressed that start with 1 aren’t insecure, but algorithms some paper wallets used at the time to create the key or password weren’t robust.

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