📅 Original date posted:2016-04-21
📝 Original message:In practice the probability of this case triggering is on the order of 2^-128 or something astronomically tiny. I've been using BIP32 for a few years already as have many others...I don't think we've ever had to handle this case. Justifiably, many app developers feel like the additional complexity of properly handling this case is not worth the effort.
Having said that, if the handling of this case is simple to implement and easy to isolate in the program flow, I am in favor of doing something along the lines of what you propose.
- Eric
On April 20, 2016 9:32:25 AM PDT, Jochen Hoenicke via bitcoin-dev <bitcoin-dev at lists.linuxfoundation.org> wrote:
>Hello Bitcoin Developers,
>
>I would like to make a proposal to update BIP-32 in a small way.
>
>TL;DR: BIP-32 is hard to use right (due to its requirement to skip
>addresses). This proposal suggests a modification such that the
>difficulty can be encapsulated in the library.
>
>#MOTIVATION:
>
>The current BIP-32 specifies that if for some node in the hierarchy
>the computed hash I_L is larger or equal to the prime or 0, then the
>node is invalid and should be skipped in the BIP-32 tree. This has
>several unfortunate consequences:
>
>- All callers of CKDpriv or CKDpub have to check for errors and handle
> them appropriately. This shifts the burden to the application
> developer instead of being able to handle it in the BIP-32 library.
>
>- It is not clear what to do if an intermediate node is
> missing. E.g. for the default wallet layout, if m/i_H/0 is missing
> should m/i_H/1 be used for external chain and m/i_H/2 for internal
> chain? This would make the wallet handling much more difficult.
>
>- It gets even worse with standards like BIP-44. If m/44' is missing
> should we use m/45' instead? If m/44'/0' is missing should we use
> m/44'/1' instead, using the same addresses as for testnet?
> One could also restart with a different seed in this case, but this
> wouldn't work if one later wants to support another BIP-43 proposal
> and still keep the same wallet.
>
>I think the first point alone is reason enough to change this. I am
>not aware of a BIP-32 application that handles errors like this
>correctly in all cases. It is also very hard to test, since it is
>infeasible to brute-force a BIP-32 key and a path where the node does
>not exists.
>
>This problem can be avoided by repeating the hashing with slightly
>different input data until a valid private key is found. This would
>be in the same spirit as RFC-6979. This way, the library will always
>return a valid node for all paths. Of course, in the case where the
>node is valid according to the current standard the behavior should be
>unchanged.
>
>I think the backward compatibility issues are minimal. The chance
>that this affects anyone is less than 10^-30. Even if it happens, it
>would only create some additional addresses (that are not seen if the
>user downgrades). The main reason for suggesting a change is that we
>want a similar method for different curves where a collision is much
>more likely.
>
>#QUESTIONS:
>
>What is the procedure to update the BIP? Is it still possible to
>change the existing BIP-32 even though it is marked as final? Or
>should I make a new BIP for this that obsoletes BIP-32?
>
>What algorithm is preferred? (bike-shedding) My suggestion:
>
>---
>
>Change the last step of the private -> private derivation functions to:
>
> . In case parse(I_L) >= n or k_i = 0, the procedure is repeated
> at step 2 with
> I = HMAC-SHA512(Key = c_par, Data = 0x01 || I_R || ser32(i))
>
>---
>
>I think this suggestion is simple to implement (a bit harder to unit
>test) and the string to hash with HMAC-SHA512 always has the same
>length. I use I_R, since I_L is obviously not very random if I_L >= n.
>There is a minimal chance that it will lead to an infinite loop if I_R
>is the same in two consecutive iterations, but that has only a chance
>of 1 in 2^512 (if the algorithm is used for different curves that make
>I_L >= n more likely, the chance is still less than 1 in 2^256). In
>theory, this loop can be avoided by incrementing i in every iteration,
>but this would make an implementation error in the "hard to test" path
>of the program more likely.
>
>The other derivation functions should be updated in a similar matter.
>Also the derivation of the root node from the seed should be updated
>in a similar matter to avoid invalid seeds.
>
>If you followed until here, thanks for reading this long posting.
>
> Jochen
>_______________________________________________
>bitcoin-dev mailing list
>bitcoin-dev at lists.linuxfoundation.org
>https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
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Eric Lombrozo [ARCHIVE] /
npub1az…t2krq
2023-06-07 17:50:10
in reply to nevent1q…t7vp
Author Public Key
npub1azvhdrf9fu6n0tm7yez4j6zcxcedp2ct6nrcq3z74naqs7kgpk8s5t2krqPublished at
2023-06-07 17:50:10Event JSON
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"content": "📅 Original date posted:2016-04-21\n📝 Original message:In practice the probability of this case triggering is on the order of 2^-128 or something astronomically tiny. I've been using BIP32 for a few years already as have many others...I don't think we've ever had to handle this case. Justifiably, many app developers feel like the additional complexity of properly handling this case is not worth the effort.\n\nHaving said that, if the handling of this case is simple to implement and easy to isolate in the program flow, I am in favor of doing something along the lines of what you propose.\n\n- Eric\n\nOn April 20, 2016 9:32:25 AM PDT, Jochen Hoenicke via bitcoin-dev \u003cbitcoin-dev at lists.linuxfoundation.org\u003e wrote:\n\u003eHello Bitcoin Developers,\n\u003e\n\u003eI would like to make a proposal to update BIP-32 in a small way.\n\u003e\n\u003eTL;DR: BIP-32 is hard to use right (due to its requirement to skip\n\u003eaddresses). This proposal suggests a modification such that the\n\u003edifficulty can be encapsulated in the library.\n\u003e\n\u003e#MOTIVATION:\n\u003e\n\u003eThe current BIP-32 specifies that if for some node in the hierarchy\n\u003ethe computed hash I_L is larger or equal to the prime or 0, then the\n\u003enode is invalid and should be skipped in the BIP-32 tree. This has\n\u003eseveral unfortunate consequences:\n\u003e\n\u003e- All callers of CKDpriv or CKDpub have to check for errors and handle\n\u003e them appropriately. This shifts the burden to the application\n\u003e developer instead of being able to handle it in the BIP-32 library.\n\u003e\n\u003e- It is not clear what to do if an intermediate node is\n\u003e missing. E.g. for the default wallet layout, if m/i_H/0 is missing\n\u003e should m/i_H/1 be used for external chain and m/i_H/2 for internal\n\u003e chain? This would make the wallet handling much more difficult.\n\u003e\n\u003e- It gets even worse with standards like BIP-44. If m/44' is missing\n\u003e should we use m/45' instead? If m/44'/0' is missing should we use\n\u003e m/44'/1' instead, using the same addresses as for testnet?\n\u003e One could also restart with a different seed in this case, but this\n\u003e wouldn't work if one later wants to support another BIP-43 proposal\n\u003e and still keep the same wallet.\n\u003e\n\u003eI think the first point alone is reason enough to change this. I am\n\u003enot aware of a BIP-32 application that handles errors like this\n\u003ecorrectly in all cases. It is also very hard to test, since it is\n\u003einfeasible to brute-force a BIP-32 key and a path where the node does\n\u003enot exists.\n\u003e\n\u003eThis problem can be avoided by repeating the hashing with slightly\n\u003edifferent input data until a valid private key is found. This would\n\u003ebe in the same spirit as RFC-6979. This way, the library will always\n\u003ereturn a valid node for all paths. Of course, in the case where the\n\u003enode is valid according to the current standard the behavior should be\n\u003eunchanged.\n\u003e\n\u003eI think the backward compatibility issues are minimal. The chance\n\u003ethat this affects anyone is less than 10^-30. Even if it happens, it\n\u003ewould only create some additional addresses (that are not seen if the\n\u003euser downgrades). The main reason for suggesting a change is that we\n\u003ewant a similar method for different curves where a collision is much\n\u003emore likely.\n\u003e\n\u003e#QUESTIONS:\n\u003e\n\u003eWhat is the procedure to update the BIP? Is it still possible to\n\u003echange the existing BIP-32 even though it is marked as final? Or\n\u003eshould I make a new BIP for this that obsoletes BIP-32?\n\u003e\n\u003eWhat algorithm is preferred? (bike-shedding) My suggestion:\n\u003e\n\u003e---\n\u003e\n\u003eChange the last step of the private -\u003e private derivation functions to:\n\u003e\n\u003e . In case parse(I_L) \u003e= n or k_i = 0, the procedure is repeated\n\u003e at step 2 with\n\u003e I = HMAC-SHA512(Key = c_par, Data = 0x01 || I_R || ser32(i))\n\u003e\n\u003e---\n\u003e\n\u003eI think this suggestion is simple to implement (a bit harder to unit\n\u003etest) and the string to hash with HMAC-SHA512 always has the same\n\u003elength. I use I_R, since I_L is obviously not very random if I_L \u003e= n.\n\u003eThere is a minimal chance that it will lead to an infinite loop if I_R\n\u003eis the same in two consecutive iterations, but that has only a chance\n\u003eof 1 in 2^512 (if the algorithm is used for different curves that make\n\u003eI_L \u003e= n more likely, the chance is still less than 1 in 2^256). In\n\u003etheory, this loop can be avoided by incrementing i in every iteration,\n\u003ebut this would make an implementation error in the \"hard to test\" path\n\u003eof the program more likely.\n\u003e\n\u003eThe other derivation functions should be updated in a similar matter.\n\u003eAlso the derivation of the root node from the seed should be updated\n\u003ein a similar matter to avoid invalid seeds.\n\u003e\n\u003eIf you followed until here, thanks for reading this long posting.\n\u003e\n\u003e Jochen\n\u003e_______________________________________________\n\u003ebitcoin-dev mailing list\n\u003ebitcoin-dev at lists.linuxfoundation.org\n\u003ehttps://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev\n-------------- next part --------------\nAn HTML attachment was scrubbed...\nURL: \u003chttp://lists.linuxfoundation.org/pipermail/bitcoin-dev/attachments/20160421/f6ea5a61/attachment.html\u003e",
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