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BIP-85: Move new reference to be near HMAC code

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Aneesh Karve 2024-11-09 14:30:02 -07:00
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1 changed files with 3 additions and 2 deletions
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@ -55,10 +55,11 @@ Ultimately, all of the mnemonic/seed schemes start with some "initial entropy" t
We assume a single BIP32 master root key. This specification is not concerned with how this was derived (e.g. directly or via a mnemonic scheme such as BIP39).
For each application that requires its own wallet, a unique private key is derived from the BIP32 master root key using a fully hardened derivation path. The resulting private key (k) is then processed with HMAC-SHA512, where the key is "bip-entropy-from-k", and the message payload is the private key k: <code>HMAC-SHA512(key="bip-entropy-from-k", msg=k)</code>. The result produces 512 bits of entropy. Each application SHOULD use up to the required number of bits necessary for their operation, and truncate the rest.
For each application that requires its own wallet, a unique private key is derived from the BIP32 master root key using a fully hardened derivation path. The resulting private key (k) is then processed with HMAC-SHA512, where the key is "bip-entropy-from-k", and the message payload is the private key k: <code>HMAC-SHA512(key="bip-entropy-from-k", msg=k)</code>
<ref name="hmac-sha512">
The reason for running the derived key through HMAC-SHA512 and truncating the result as necessary is to prevent leakage of the parent tree should the derived key (''k'') be compromised. While the specification requires the use of hardended key derivation which would prevent this, we cannot enforce hardened derivation, so this method ensures the derived entropy is hardened. Also, from a semantic point of view, since the purpose is to derive entropy and not a private key, we are required to transform the child key. This is done out of an abundance of caution, in order to ward off unwanted side effects should ''k'' be used for a dual purpose, including as a nonce ''hash(k)'', where undesirable and unforeseen interactions could occur.
</ref>
</ref>.
The result produces 512 bits of entropy. Each application SHOULD use up to the required number of bits necessary for their operation, and truncate the rest.
The HMAC-SHA512 function is specified in [https://tools.ietf.org/html/rfc4231 RFC 4231].