91 lines
2.8 KiB
Go
91 lines
2.8 KiB
Go
package shachain
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import (
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"io"
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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)
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// Producer is an interface which serves as an abstraction over the data
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// structure responsible for efficiently generating the secrets for a
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// particular index based on a root seed. The generation of secrets should be
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// made in such way that secret store might efficiently store and retrieve the
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// secrets. This is typically implemented as a tree-based PRF.
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type Producer interface {
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// AtIndex produces a secret by evaluating using the initial seed and a
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// particular index.
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AtIndex(uint64) (*chainhash.Hash, error)
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// Encode writes a binary serialization of the Producer implementation
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// to the passed io.Writer.
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Encode(io.Writer) error
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}
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// RevocationProducer is an implementation of Producer interface using the
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// shachain PRF construct. Starting with a single 32-byte element generated
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// from a CSPRNG, shachain is able to efficiently generate a nearly unbounded
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// number of secrets while maintaining a constant amount of storage. The
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// original description of shachain can be found here:
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// https://github.com/rustyrussell/ccan/blob/master/ccan/crypto/shachain/design.txt
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// with supplementary material here:
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// https://github.com/lightningnetwork/lightning-rfc/blob/master/03-transactions.md#per-commitment-secret-requirements
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type RevocationProducer struct {
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// root is the element from which we may generate all hashes which
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// corresponds to the index domain [281474976710655,0].
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root *element
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}
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// A compile time check to ensure RevocationProducer implements the Producer
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// interface.
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var _ Producer = (*RevocationProducer)(nil)
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// NewRevocationProducer creates new instance of shachain producer.
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func NewRevocationProducer(root chainhash.Hash) *RevocationProducer {
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return &RevocationProducer{
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root: &element{
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index: rootIndex,
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hash: root,
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}}
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}
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// NewRevocationProducerFromBytes deserializes an instance of a
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// RevocationProducer encoded in the passed byte slice, returning a fully
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// initialized instance of a RevocationProducer.
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func NewRevocationProducerFromBytes(data []byte) (*RevocationProducer, error) {
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root, err := chainhash.NewHash(data)
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if err != nil {
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return nil, err
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}
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return &RevocationProducer{
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root: &element{
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index: rootIndex,
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hash: *root,
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},
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}, nil
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}
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// AtIndex produces a secret by evaluating using the initial seed and a
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// particular index.
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//
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// NOTE: Part of the Producer interface.
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func (p *RevocationProducer) AtIndex(v uint64) (*chainhash.Hash, error) {
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ind := newIndex(v)
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element, err := p.root.derive(ind)
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if err != nil {
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return nil, err
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}
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return &element.hash, nil
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}
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// Encode writes a binary serialization of the Producer implementation to the
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// passed io.Writer.
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//
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// NOTE: Part of the Producer interface.
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func (p *RevocationProducer) Encode(w io.Writer) error {
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_, err := w.Write(p.root.hash[:])
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return err
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}
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