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vendor/github.com/hdevalence/ed25519consensus/README.md

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+# Ed25519 for consensus-critical contexts
+
+This library provides an Ed25519 implementation with validation rules intended
+for consensus-critical contexts.
+
+Ed25519 signatures are widely used in consensus-critical contexts (e.g.,
+blockchains), where different nodes must agree on whether or not a given
+signature is valid.  However, Ed25519 does not clearly define criteria for
+signature validity, and even standards-conformant implementations are not
+required to agree on whether a signature is valid.
+
+Different Ed25519 implementations may not (and in practice, do not) agree on
+validation criteria in subtle edge cases.   This poses a double risk to the use
+of Ed25519 in consensus-critical contexts.  First, the presence of multiple
+Ed25519 implementations may open the possibility of consensus divergence.
+Second, even when a single implementation is used, the protocol implicitly
+includes that particular version's validation criteria as part of the consensus
+rules.  However, if the implementation is not intended to be used in
+consensus-critical contexts, it may change validation criteria between releases.
+
+For instance, the initial implementation of Zcash consensus in zcashd inherited
+validity criteria from a then-current version of libsodium (1.0.15). Due to a
+bug in libsodium, this was different from the intended criteria documented in
+the Zcash protocol specification 3 (before the specification was changed to
+match libsodium 1.0.15 in specification version 2020.1.2). Also, libsodium
+never guaranteed stable validity criteria, and changed behavior in a later
+point release. This forced zcashd to use an older version of the library before
+eventually patching a newer version to have consistent validity criteria. To be
+compatible, Zebra had to implement a special library, ed25519-zebra to provide
+Zcash-flavored Ed25519, attempting to match libsodium 1.0.15 exactly. And the
+initial attempt to implement ed25519-zebra was also incompatible, because it
+precisely matched the wrong compile-time configuration of libsodium.
+
+This problem is fixed by [ZIP215], a specification of a precise set of
+validation criteria for Ed25519 signatures.
+This repository contains a fork of Go's `crypto/ed25519` package with support
+for [ZIP215] verification.
+
+Note that the ZIP215 rules ensure that individual and batch verification are
+guaranteed to give the same results, so unlike `ed25519.Verify`, `ed25519consensus.Verify` is
+compatible with batch verification.
+
+[ZIP215]: https://zips.z.cash/zip-0215