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graph.go
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graph.go
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package vcrypt
import (
"bytes"
"crypto/rand"
"errors"
"github.com/vcrypt/vcrypt/cryptex"
"github.com/vcrypt/vcrypt/graph"
"github.com/vcrypt/vcrypt/secret"
)
// Graph encodes an encryption plan into discrete steps represented as Nodes.
type Graph struct {
*graph.DAG
digests, nonces map[*graph.Vertex][]byte
}
// NewGraph constructs a graph with a root Node for cptx.
func NewGraph(cptx cryptex.Cryptex) (*Graph, error) {
env, err := cryptex.Wrap(cptx)
if err != nil {
return nil, err
}
return &Graph{
DAG: graph.NewDAG(env),
digests: make(map[*graph.Vertex][]byte),
nonces: make(map[*graph.Vertex][]byte),
}, nil
}
// BuildGraph constructs a graph from a slice of Nodes.
func BuildGraph(nodes []*Node) (*Graph, error) {
cptx, err := nodes[0].Cryptex()
if err != nil {
return nil, err
}
if cptx == nil {
return nil, errors.New("root node is non cryptex")
}
g, err := NewGraph(cptx)
if err != nil {
return nil, err
}
fp, err := nodes[0].Digest()
if err != nil {
return nil, err
}
g.digests[g.Root] = fp
g.nonces[g.Root] = nodes[0].Nonce
vertMap := map[string]*graph.Vertex{
string(fp): g.Root,
}
// insert verts
for _, node := range nodes[1:] {
var val interface{}
switch node.Type() {
case CryptexNode:
cptx, err := node.Cryptex()
if err != nil {
return nil, err
}
if val, err = cryptex.Wrap(cptx); err != nil {
return nil, err
}
case SecretNode:
sec, err := node.Secret()
if err != nil {
return nil, err
}
if val, err = secret.Wrap(sec); err != nil {
return nil, err
}
case MarkerNode:
val = node.Marker
default:
panic("unreachable")
}
v := g.DAG.Add(val)
fp, err := node.Digest()
if err != nil {
return nil, err
}
g.digests[v] = fp
g.nonces[v] = node.Nonce
vertMap[string(fp)] = v
}
// add edges
for _, node := range nodes {
fromfp, err := node.Digest()
if err != nil {
return nil, err
}
for _, tofp := range node.Inputs {
to, from := vertMap[string(tofp)], vertMap[string(fromfp)]
if err := g.AddEdge(to, from); err != nil {
return nil, err
}
}
}
return g, nil
}
// Add inserts a new Node into the graph with a parent edge from the vertex.
func (g *Graph) Add(val interface{}, from *graph.Vertex) (*graph.Vertex, error) {
to := g.DAG.Add(val)
return to, g.AddEdge(to, from)
}
// Nodes converts the graph vertecies into Nodes in consistent reverse
// depth-first order.
func (g *Graph) Nodes() ([]*Node, error) {
nodes := make([]*Node, 0, len(g.Adjacency))
walker := func(v *graph.Vertex) error {
node, err := g.node(v)
if err != nil {
return err
}
fp, err := node.Digest()
if err != nil {
return err
}
nodes = append([]*Node{node}, nodes...) // push front so Root is first
g.digests[v] = fp
g.nonces[v] = node.Nonce
return nil
}
if err := g.DAG.ReverseDFS(walker); err != nil {
return nil, err
}
return nodes, nil
}
func (g *Graph) node(v *graph.Vertex) (*Node, error) {
edgeList, ok := g.Adjacency[v]
if !ok {
return nil, errors.New("vertex missing in DAG")
}
nonce := g.nonces[v]
if nonce == nil {
nonce = g.genNonce()
}
inputs := make([][]byte, 0, edgeList.Len())
for e := edgeList.Front(); e != nil; e = e.Next() {
v := e.Value.(*graph.Vertex)
fp, ok := g.digests[v]
if !ok {
return nil, errors.New("reached parent vertex before child")
}
inputs = append(inputs, fp)
}
switch v := v.Value.(type) {
case *cryptex.Envelope:
return &Node{
Nonce: nonce,
Inputs: inputs,
cryptex: v,
}, nil
case *secret.Envelope:
return &Node{
Nonce: nonce,
Inputs: inputs,
secret: v,
}, nil
case *Marker:
return &Node{
Nonce: nonce,
Inputs: inputs,
Marker: v,
}, nil
default:
return nil, errors.New("invalid graph Vertex value")
}
}
func (g *Graph) genNonce() []byte {
for {
nonce := make([]byte, 8)
if _, err := rand.Read(nonce); err != nil {
panic(err)
}
collision := false
for _, n := range g.nonces {
if bytes.Equal(nonce, n) {
collision = true
}
}
if !collision {
return nonce
}
}
}