Just a small question. Wouldn't this make it easier for an unauthorized individual to make a copy of the wallet and then use it at an arbitrary date in the future to access and steal any coins in it?
Topic: Deterministic wallets - page 16. (Read 48389 times)
I like this idea. A lot. I'm not a cryptologist but I can't think of any downside to this other than one possible (if unlikely) one: what if generating 1000 addresses past the last one seen in the chain isn't enough? After all, a user can generate then discard an arbitrary number of addresses for use, but the code as described would only look for the first 1000 addresses past the last one seen (I assume it would initially look for any of the first 1000 addresses.) But then even this could be handled by a "look for more of my addresses" button that looks for the next 1000 addresses.
Lack of backwards-compatibilty of the new wallets might be an issue, but surely not a significant one (especially if the clients using deterministic wallets would still be able to read and continue growing older wallets.)
So, yeah, no obvious downside that I can see. Who do I pay to get this into a client?
Lack of backwards-compatibilty of the new wallets might be an issue, but surely not a significant one (especially if the clients using deterministic wallets would still be able to read and continue growing older wallets.)
So, yeah, no obvious downside that I can see. Who do I pay to get this into a client?
"in general" session-based components/"smoking crypto" in crypto-systems are nice to strengthen them w/o overhead increase and used by military from WWII era.
so, IMO, its[impact] worth code grow.
so, IMO, its[impact] worth code grow.
Definately worth of inclusion.
+1
+1
I like this idea.
Will
Will
The purpose is clear and definitely appealing.
Type-2 might indeed be a good implementation, but I don't think I understand Type-1.
You would use H(n|S|type) to seed a keypair generation? Isn't the data too small for that purpose?
Or H would not be the usual kind of hash function, maybe a symmetric cypher?
Type-2 might indeed be a good implementation, but I don't think I understand Type-1.
You would use H(n|S|type) to seed a keypair generation? Isn't the data too small for that purpose?
Or H would not be the usual kind of hash function, maybe a symmetric cypher?
ECC != RSA. You only need as much data is in a private key to create one.
The purpose is clear and definitely appealing.
Type-2 might indeed be a good implementation, but I don't think I understand Type-1.
You would use H(n|S|type) to seed a keypair generation? Isn't the data too small for that purpose?
Or H would not be the usual kind of hash function, maybe a symmetric cypher?
Type-2 might indeed be a good implementation, but I don't think I understand Type-1.
You would use H(n|S|type) to seed a keypair generation? Isn't the data too small for that purpose?
Or H would not be the usual kind of hash function, maybe a symmetric cypher?
I've discussed this enough on IRC that I thought I ought to put it someplace more lasting.
Bitcoin really ought to offer and default to using deterministic wallets. The additional security of the current pre-generated ones is fairly small considering how most people use bitcoin and the liability of harm due to insufficient backups and increased pressure to keep a single wallet online is enormous.
What is a deterministic wallet? It's a wallet which you can backup once and it stays backed up forever because all future addresses are determined in advance. It can also be stripped down to a very small size which could be easily backed up on paper (e.g. with a QR code). This is in contrast to the current non-determinstic wallets where the keys are random but are precomputed ahead so that you're safe only if you backup at least every 100 get addresses or sends, and which grow large and harder to backup on paper over time.
I've found the backup behavior of the current wallets fairly difficulty to get even moderately technical people to understand. The current system provides enough safety to encourage complacency but not enough to make complacency acceptable. The positive side of a non-determistic wallet is that it becomes "unstolen" over time but people are frequently reusing addresses and attackers will not act slowly regardless.
There are two types of deterministic wallet I'd like to discuss. I'll call them type-1 and type-2.
Type-1 is the most obvious kind:
The wallet stores a large random seed S (which can be encrypted if the user uses wallet encryption)
Privatekey(type,n) is then simply set to H(n|S|type) where H is an acceptable secure hash function and type can be set to different values for change addresses vs displayed addresses (so this distinction is preserved even if new wallet metadata is lost).
The system would generate some (maybe 1000 of each type) addresses ahead of the furthest it has observed on the network but only bother to store the addresses. The keys can be regenerated as needed.
Type-2 is a bit less obvious and understanding it requires you to know about a property of ECC keys, roughly:
A_public_key = A_private_key*point
Which means you can do:
B_public_key = A_public_key+B_secret*point
and have a new key which has a private key:
B_private_key = A_private_key+B_secret
So a type2 wallet stores:
Master_private_key
A large Random_seed S.
and keys are given by
Privatekey(type,n) = Master_private_key + H(n|S|type)
which works just like a type-1, the advantage of the type-2 is that you can separately secure the Master_private_key, but still generate new addresses with
Publickey(type,n) = Master_public_key + H(n|S|type)*point
This means that a e-commerce site could have the front end webserver with access to the public key and S, and someone who hacked the server could violate the confidentiality of the addresses in use (because he could enumerate all past and future addresses based on an infrequently changed public key) but couldn't actually steal any of they money sent to the addresses because he would have no access to the private keys.
This could also be used to allow getaddress to work in the client without having to provide a key (access to the TXN data in the wallet means that access to the wallet, even with private key encryption, screws your confidentiality) which would avoid the problem of backups being endangered due to address depletion from hitting getaddress a lot between entering in the key.
Bitcoin really ought to offer and default to using deterministic wallets. The additional security of the current pre-generated ones is fairly small considering how most people use bitcoin and the liability of harm due to insufficient backups and increased pressure to keep a single wallet online is enormous.
What is a deterministic wallet? It's a wallet which you can backup once and it stays backed up forever because all future addresses are determined in advance. It can also be stripped down to a very small size which could be easily backed up on paper (e.g. with a QR code). This is in contrast to the current non-determinstic wallets where the keys are random but are precomputed ahead so that you're safe only if you backup at least every 100 get addresses or sends, and which grow large and harder to backup on paper over time.
I've found the backup behavior of the current wallets fairly difficulty to get even moderately technical people to understand. The current system provides enough safety to encourage complacency but not enough to make complacency acceptable. The positive side of a non-determistic wallet is that it becomes "unstolen" over time but people are frequently reusing addresses and attackers will not act slowly regardless.
There are two types of deterministic wallet I'd like to discuss. I'll call them type-1 and type-2.
Type-1 is the most obvious kind:
The wallet stores a large random seed S (which can be encrypted if the user uses wallet encryption)
Privatekey(type,n) is then simply set to H(n|S|type) where H is an acceptable secure hash function and type can be set to different values for change addresses vs displayed addresses (so this distinction is preserved even if new wallet metadata is lost).
The system would generate some (maybe 1000 of each type) addresses ahead of the furthest it has observed on the network but only bother to store the addresses. The keys can be regenerated as needed.
Type-2 is a bit less obvious and understanding it requires you to know about a property of ECC keys, roughly:
A_public_key = A_private_key*point
Which means you can do:
B_public_key = A_public_key+B_secret*point
and have a new key which has a private key:
B_private_key = A_private_key+B_secret
So a type2 wallet stores:
Master_private_key
A large Random_seed S.
and keys are given by
Privatekey(type,n) = Master_private_key + H(n|S|type)
which works just like a type-1, the advantage of the type-2 is that you can separately secure the Master_private_key, but still generate new addresses with
Publickey(type,n) = Master_public_key + H(n|S|type)*point
This means that a e-commerce site could have the front end webserver with access to the public key and S, and someone who hacked the server could violate the confidentiality of the addresses in use (because he could enumerate all past and future addresses based on an infrequently changed public key) but couldn't actually steal any of they money sent to the addresses because he would have no access to the private keys.
This could also be used to allow getaddress to work in the client without having to provide a key (access to the TXN data in the wallet means that access to the wallet, even with private key encryption, screws your confidentiality) which would avoid the problem of backups being endangered due to address depletion from hitting getaddress a lot between entering in the key.
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