This repository has been archived by the owner on Jun 3, 2020. It is now read-only.
yubihsm setup: use hkd32 crate to derive key hierarchy #302
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
`hkd32` is an implementation of the same hierarchical key derivation algorithm the KMS was previously using, which is an extracted subset of the symmetric parts of BIP32 derivation (to the point it could potentially be used to implement a full BIP32). The `hkd32` crate has the advantage of using a zeroize-on-drop type for all key material, as opposed to some of the manual zeroization this crate was previously using. In addition, it has some richer types for things like derivation paths, which may be potentially useful in the future. There is one case that deviated from the previous implementation, which is the behavior of calling derive with an empty derivation path. Before it would output the "chain code" derived after inputting the `DERIVATION_VERSION`, whereas when using `hkd32` it correctly outputs the other half of the derived key material, which is intended to be used as a secret key. Nothing presently calls the derivation function with an empty derivation path, except for a test I just added today in #299. While the output for this case differs, it has no practical impact, and if anything the function outputting the raw chain code for the first level of the hierarchy (which is the version number) is a sharp edge that could potentially leak what is the root key to the entire hierarchy if it were to be called with an empty derivation path. `hkd32` uses a fully uniform derivation algorithm which treats the `DERIVATION_VERSION` like any other part of the path, and therefore does not have this sharp edge. Test vectors for path lengths of 1, 2, and 3 all pass with the original vectors.
This was referenced Jul 25, 2019
Merged
Closed
Merged
Sign up for free
to subscribe to this conversation on GitHub.
Already have an account?
Sign in.
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
hkd32 is an implementation of the same hierarchical key derivation algorithm the KMS was previously using, which is an extracted subset of the symmetric parts of BIP32 derivation (to the point it could potentially be used to implement a full BIP32).
The
hkd32crate has the advantage of using a zeroize-on-drop type for all key material, as opposed to some of the manual zeroization this crate was previously using. In addition, it has some richer types for things like derivation paths, which may be potentially useful in the future.There is one case that deviated from the previous implementation, which is the behavior of calling derive with an empty derivation path. Before it would output the "chain code" derived after inputting the
DERIVATION_VERSION, whereas when usinghkd32it correctly outputs the other half of the derived key material, which is intended to be used as a secret key.Nothing presently calls the derivation function with an empty derivation path, except for a test I just added today in #299. While the output for this case differs, it has no practical impact, and if anything the function outputting the raw chain code for the first level of the hierarchy (which is the version number) is a sharp edge that could potentially leak what is the root key to the entire hierarchy if it were to be called with an empty derivation path.
hkd32uses a fully uniform derivation algorithm which treats theDERIVATION_VERSIONlike any other part of the path, and therefore does not have this sharp edge.Test vectors for path lengths of 1, 2, and 3 all pass with the original vectors.