Bind Agent execution to task providers and SIP revision

internal/configread/binding.go

@@ -0,0 +1,29 @@
+package configread
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+)
+
+// ExecutionBindingSHA256 binds the exact immutable task and provider bytes
+// to the SIP revision delivered to an Agent. Length prefixes prevent
+// concatenation collisions; no credential content is returned or logged.
+func ExecutionBindingSHA256(taskJSON, providersJSON []byte, sipRevision int64) (string, error) {
+	if !json.Valid(taskJSON) || !json.Valid(providersJSON) || sipRevision <= 0 {
+		return "", errors.New("execution snapshot has invalid JSON or SIP revision")
+	}
+	h := sha256.New()
+	var number [8]byte
+	binary.BigEndian.PutUint64(number[:], uint64(len(taskJSON)))
+	_, _ = h.Write(number[:])
+	_, _ = h.Write(taskJSON)
+	binary.BigEndian.PutUint64(number[:], uint64(len(providersJSON)))
+	_, _ = h.Write(number[:])
+	_, _ = h.Write(providersJSON)
+	binary.BigEndian.PutUint64(number[:], uint64(sipRevision))
+	_, _ = h.Write(number[:])
+	return hex.EncodeToString(h.Sum(nil)), nil
+}

internal/configread/binding_test.go

@@ -0,0 +1,51 @@
+package configread
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestExecutionBindingSHA256CoversTaskProvidersAndSIPRevision(t *testing.T) {
+	task, err := os.ReadFile("../../contracts/local/examples/config-read-task-full.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	providers, err := os.ReadFile("../../contracts/local/examples/config-read-providers.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	original, err := ExecutionBindingSHA256(task, providers, 8)
+	if err != nil || len(original) != 64 {
+		t.Fatalf("binding hash: %q %v", original, err)
+	}
+	changedTask := append(append([]byte(nil), task...), ' ')
+	changedProviders := append(append([]byte(nil), providers...), ' ')
+	for _, tc := range []struct {
+		name      string
+		task      []byte
+		providers []byte
+		revision  int64
+	}{
+		{"task", changedTask, providers, 8},
+		{"providers", task, changedProviders, 8},
+		{"sip-revision", task, providers, 9},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := ExecutionBindingSHA256(tc.task, tc.providers, tc.revision)
+			if err != nil || got == original {
+				t.Fatalf("snapshot field not bound: %q %v", got, err)
+			}
+		})
+	}
+	for _, tc := range []struct {
+		task, providers []byte
+		revision        int64
+	}{
+		{nil, providers, 8}, {task, nil, 8}, {[]byte(`not-json`), providers, 8}, {task, providers, 0},
+	} {
+		if _, err := ExecutionBindingSHA256(tc.task, tc.providers, tc.revision); err == nil || strings.Contains(err.Error(), "example-only-not-a-real-secret") {
+			t.Fatalf("invalid binding must be rejected without printing provider credentials: %v", err)
+		}
+	}
+}