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CH08: update RFC6979 text to describe BIP340 and synthentic nonces

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This commit is contained in:
David A. Harding 2023-03-31 08:20:36 -10:00
parent 5f4a8cfc66
commit a28d4bb054
1 changed files with 18 additions and 7 deletions
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25
chapters/signatures.adoc
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@ -364,6 +364,7 @@ See if you can decode Alice's serialized (DER-encoded) signature using
this list. The important numbers are +R+ and +S+; the rest of the data this list. The important numbers are +R+ and +S+; the rest of the data
is part of the DER encoding scheme. is part of the DER encoding scheme.
[[nonce_warning]]
=== The Importance of Randomness in Signatures === The Importance of Randomness in Signatures
((("digital signatures", "randomness in")))As we saw in <<ecdsa_math>>, ((("digital signatures", "randomness in")))As we saw in <<ecdsa_math>>,
@ -392,15 +393,25 @@ generator.
((("random numbers", "random number generation")))((("entropy", "random ((("random numbers", "random number generation")))((("entropy", "random
number generation")))((("deterministic initialization")))To avoid this number generation")))((("deterministic initialization")))To avoid this
vulnerability, the industry best practice is to not generate _k_ with a vulnerability, the industry best practice is to not generate _k_ with a
random-number generator seeded with entropy, but instead to use a random-number generator seeded only with entropy, but instead to use a
deterministic-random process seeded with the transaction data itself. process seeded in part with the transaction data itself.
This ensures that each transaction produces a different _k_. The This ensures that each transaction produces a different _k_. The
industry-standard algorithm for deterministic initialization of _k_ is industry-standard algorithm for deterministic initialization of _k_ for
defined in https://tools.ietf.org/html/rfc6979[RFC 6979], published by ECDSA is defined in https://tools.ietf.org/html/rfc6979[RFC6979], published by
the Internet Engineering Task Force. the Internet Engineering Task Force. For schnorr signatures, BIP340
recommends a default signing algorithm.
If you are implementing an algorithm to sign transactions in bitcoin, BIP340 and RFC6979 can generate _k_ entirely deterministically, meaning the same
you _must_ use RFC 6979 or a similarly deterministic-random algorithm to transaction data will always produce the same _k_. Many wallets do this
because it makes it easy to write tests to verify their safety-critical
signing code is producing _k_ values correctly. RFC6979 also allows
including additional data in the calculation. If that data is entropy,
then a different _k_ will be produced even if the exact same transaction
data is signed. This can increase protection against sidechannel and
fault-injection attacks.
If you are implementing an algorithm to sign transactions in Bitcoin,
you _must_ use BIP340, RFC6979, or a similar algorithm to
ensure you generate a different _k_ for each transaction.((("", ensure you generate a different _k_ for each transaction.((("",
startref="Tdigsig06"))) startref="Tdigsig06")))