shachain: complete shachain implementation

shachain/producer.go

@@ -0,0 +1,76 @@
+package shachain
+
+import (
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
+)
+
+// Producer is an interface which serves as an abstraction over data
+// structure responsible for efficient generating the secrets by given index.
+// The generation of secrets should be made in such way that secret store
+// might efficiently store and retrieve the secrets.
+type Producer interface {
+	// AtIndex produce secret by given index.
+	AtIndex(uint64) (*chainhash.Hash, error)
+
+	// ToBytes convert producer to the binary representation.
+	ToBytes() ([]byte, error)
+}
+
+// RevocationProducer implementation of Producer. This version of shachain
+// slightly changed in terms of method naming. Initial concept might be found
+// here:
+// https://github.com/rustyrussell/ccan/blob/master/ccan/crypto/shachain/design.txt
+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 create new instance of shachain producer.
+func NewRevocationProducer(root *chainhash.Hash) *RevocationProducer {
+	return &RevocationProducer{
+		root: &element{
+			index: rootIndex,
+			hash:  *root,
+		}}
+}
+
+// NewRevocationProducerFromBytes deserialize an instance of a RevocationProducer
+// encoded in the passed byte slice, returning a fully initialize 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 produce secret by given 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
+}
+
+// ToBytes convert producer to the binary representation.
+// NOTE: Part of the Producer interface.
+func (p *RevocationProducer) ToBytes() ([]byte, error) {
+	return p.root.hash.CloneBytes(), nil
+}