Release v0.3.0

vendor/github.com/lightningnetwork/lnd/shachain/producer.go

@@ -0,0 +1,90 @@
+package shachain
+
+import (
+	"io"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+)
+
+// Producer is an interface which serves as an abstraction over the data
+// structure responsible for efficiently generating the secrets for a
+// particular index based on a root seed.  The generation of secrets should be
+// made in such way that secret store might efficiently store and retrieve the
+// secrets. This is typically implemented as a tree-based PRF.
+type Producer interface {
+	// AtIndex produces a secret by evaluating using the initial seed and a
+	// particular index.
+	AtIndex(uint64) (*chainhash.Hash, error)
+
+	// Encode writes a binary serialization of the Producer implementation
+	// to the passed io.Writer.
+	Encode(io.Writer) error
+}
+
+// RevocationProducer is an implementation of Producer interface using the
+// shachain PRF construct. Starting with a single 32-byte element generated
+// from a CSPRNG, shachain is able to efficiently generate a nearly unbounded
+// number of secrets while maintaining a constant amount of storage. The
+// original description of shachain can be found here:
+// https://github.com/rustyrussell/ccan/blob/master/ccan/crypto/shachain/design.txt
+// with supplementary material here:
+// https://github.com/lightningnetwork/lightning-rfc/blob/master/03-transactions.md#per-commitment-secret-requirements
+type RevocationProducer struct {
+	// root is the element from which we may generate all hashes which
+	// corresponds to the index domain [281474976710655,0].
+	root *element
+}
+
+// A compile time check to ensure RevocationProducer implements the Producer
+// interface.
+var _ Producer = (*RevocationProducer)(nil)
+
+// NewRevocationProducer creates new instance of shachain producer.
+func NewRevocationProducer(root chainhash.Hash) *RevocationProducer {
+	return &RevocationProducer{
+		root: &element{
+			index: rootIndex,
+			hash:  root,
+		}}
+}
+
+// NewRevocationProducerFromBytes deserializes an instance of a
+// RevocationProducer encoded in the passed byte slice, returning a fully
+// initialized instance of a RevocationProducer.
+func NewRevocationProducerFromBytes(data []byte) (*RevocationProducer, error) {
+	root, err := chainhash.NewHash(data)
+	if err != nil {
+		return nil, err
+	}
+
+	return &RevocationProducer{
+		root: &element{
+			index: rootIndex,
+			hash:  *root,
+		},
+	}, nil
+}
+
+// AtIndex produces a secret by evaluating using the initial seed and a
+// particular index.
+//
+// NOTE: Part of the Producer interface.
+func (p *RevocationProducer) AtIndex(v uint64) (*chainhash.Hash, error) {
+	ind := newIndex(v)
+
+	element, err := p.root.derive(ind)
+	if err != nil {
+		return nil, err
+	}
+
+	return &element.hash, nil
+}
+
+// Encode writes a binary serialization of the Producer implementation to the
+// passed io.Writer.
+//
+// NOTE: Part of the Producer interface.
+func (p *RevocationProducer) Encode(w io.Writer) error {
+	_, err := w.Write(p.root.hash[:])
+	return err
+}