DateKeys/capsule/fuzz_test.go

package capsule_test

import (
	"bytes"
	"context"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"testing"

	datekeys "g.activething.com/go/DateKeys"
	"g.activething.com/go/DateKeys/accesskey"
	"g.activething.com/go/DateKeys/capsule"
	"g.activething.com/go/DateKeys/datekey"
	"g.activething.com/go/DateKeys/extension"
	"g.activething.com/go/DateKeys/internal/testkit"
	"g.activething.com/go/DateKeys/profile"
)

func seedFixtures(f *testing.F, part func(testkit.Parts) []byte) {
	for _, name := range fixtureNames {
		b, err := os.ReadFile(filepath.Join(fixtureDir, name+".dkc"))
		if err != nil {
			f.Fatal(err)
		}
		p, err := testkit.Split(b)
		if err != nil {
			f.Fatal(err)
		}
		f.Add(part(p))
	}
}

// whole keeps the first 512 bytes of the payload: the pre-unlock checks read
// only its age header, and small inputs keep the fuzzer fast.
func whole(p testkit.Parts) []byte {
	payload := p.Payload
	if len(payload) > 512 {
		payload = payload[:512]
	}
	return testkit.Join(p.Prelude, p.Header, p.Sealed, payload)
}

func FuzzParsePrelude(f *testing.F) {
	seedFixtures(f, func(p testkit.Parts) []byte { return p.Prelude })
	f.Fuzz(func(t *testing.T, b []byte) {
		p, err := capsule.ParsePrelude(b)
		if err != nil {
			if datekeys.Code(err) == "" {
				t.Fatalf("error without a normative code: %v", err)
			}
			return
		}
		got := p.Bytes()
		if !bytes.Equal(got[:], b[:capsule.PreludeSize]) {
			t.Fatal("accepted a prelude that does not re-encode to its input")
		}
	})
}

func FuzzDecodeHeader(f *testing.F) {
	seedFixtures(f, func(p testkit.Parts) []byte { return p.Header })
	// access_policy in a multi-byte head whose low byte is a V1 policy: a
	// narrowing before the check accepted them (spec §25).
	dk := datekey.DateKey{ProfileID: profile.QuicknetID, Round: 1000}.Compact()
	for _, p := range []uint64{256, 257, 1 << 32} {
		h, err := testkit.RawHeader([capsule.CapsuleIDSize]byte{1}, dk, p)
		if err != nil {
			f.Fatal(err)
		}
		f.Add(h)
	}
	f.Fuzz(func(t *testing.T, b []byte) {
		h, err := capsule.DecodeHeader(b)
		if err != nil {
			if datekeys.Code(err) == "" {
				t.Fatalf("error without a normative code: %v", err)
			}
			return
		}
		re, err := capsule.EncodeHeader(h)
		if err != nil || !bytes.Equal(re, b) {
			t.Fatal("accepted a PUBLIC_HEADER that does not re-encode to its input")
		}
	})
}

func FuzzDecodeControl(f *testing.F) {
	for _, name := range fixtureNames {
		fx := loadFixture(f, name)
		b, _ := hexDecode(fx.ControlCBOR)
		f.Add(b)
	}
	f.Fuzz(func(t *testing.T, b []byte) {
		// The same bytes as the control of a capsule of each format: at most
		// one of the two schema versions accepts them.
		accepted := 0
		for _, format := range []capsule.Format{capsule.Format1, capsule.Format2} {
			c, err := capsule.DecodeControl(b, format)
			if err != nil {
				if datekeys.Code(err) == "" {
					t.Fatalf("format %d: error without a normative code: %v", format, err)
				}
				continue
			}
			accepted++
			re, err := capsule.EncodeControl(c, format)
			if err != nil || !bytes.Equal(re, b) {
				t.Fatalf("format %d: accepted a CONTROL_CBOR that does not re-encode to its input", format)
			}
		}
		if accepted > 1 {
			t.Fatal("both formats accept the same CONTROL_CBOR")
		}
	})
}

// FuzzInspect feeds whole capsules to the pre-unlock validation, and to Open
// with a source that never has the release: a capsule that Inspect rejects
// must not cause a request, and nothing may pass the release step. The
// cryptographic steps after it are exercised by the mutation corpus; keeping
// them out of this target keeps it fast.
func FuzzInspect(f *testing.F) {
	seedFixtures(f, whole)
	reg := testkit.Registry()
	far := testkit.Fixed(testkit.Genesis().AddDate(5, 0, 0))
	f.Fuzz(func(t *testing.T, b []byte) {
		_, err := capsule.Inspect(bytes.NewReader(b), capsule.InspectOptions{Registry: reg})
		if err != nil && datekeys.Code(err) == "" {
			t.Fatalf("error without a normative code: %v", err)
		}
		src := testkit.NewSource()
		o := capsule.OpenOptions{Registry: reg, Source: src, Now: far}
		_, openErr := capsule.Open(context.Background(), io.Discard, bytes.NewReader(b), o)
		switch {
		case openErr == nil:
			t.Fatal("opened without a release")
		case datekeys.Code(openErr) == "":
			t.Fatalf("error without a normative code: %v", openErr)
		case err != nil && src.Calls != 0:
			t.Fatal("a capsule rejected by Inspect caused a release request")
		case err == nil && !errors.Is(openErr, datekeys.ErrReleaseUnavailable) && !errors.Is(openErr, datekeys.ErrAccessRequired):
			t.Fatalf("a capsule accepted by Inspect failed before the release step: %v", openErr)
		}
	})
}

// FuzzEncodeImpliesDecode: whatever EncodeHeader, EncodeControl and
// accesskey.Encode accept, the matching decoder accepts and re-encodes to the
// same bytes. An encoder that writes what its reader rejects makes capsules
// that cannot be opened (spec §72, §76 case 5).
func FuzzEncodeImpliesDecode(f *testing.F) {
	f.Add("org.example.label", uint64(1), []byte("public label"), "org.example.note", uint64(2), []byte{0xa2, 0x00, 0x07}, uint8(0), uint8(0))
	f.Add("a", uint64(1)<<32, []byte{}, "a", uint64(0), []byte{0x81, 0x81, 0x00}, uint8(0b1011), uint8(63))
	f.Add("org.\xff", uint64(0), []byte{0xf6}, "z", uint64(1)<<53, []byte(nil), uint8(0b0100), uint8(64))
	dk := datekey.DateKey{ProfileID: profile.QuicknetID, Round: 1000}
	f.Fuzz(func(t *testing.T, id1 string, v1 uint64, d1 []byte, id2 string, v2 uint64, d2 []byte, mode, filler uint8) {
		// mode bit 0: first extension critical; bit 1: second critical;
		// bit 2: first without data; bit 3: second without data. filler
		// adds extensions to the noncritical array, up to past the limit.
		e1 := extension.Extension{ID: id1, Version: v1, Data: d1}
		e2 := extension.Extension{ID: id2, Version: v2, Data: d2}
		if mode&4 != 0 {
			e1.Data = nil
		}
		if mode&8 != 0 {
			e2.Data = nil
		}
		var crit, non []extension.Extension
		for i, e := range []extension.Extension{e1, e2} {
			if mode&(1<<i) != 0 {
				crit = append(crit, e)
			} else {
				non = append(non, e)
			}
		}
		for i := range int(filler % 72) {
			non = append(non, extension.Extension{ID: fmt.Sprintf("x.%02d", i), Version: 1})
		}

		h := &capsule.Header{DateKey: dk, Policy: capsule.Policy(mode >> 4 & 1), Critical: crit, Noncritical: non}
		if b, err := capsule.EncodeHeader(h); err == nil {
			back, err := capsule.DecodeHeader(b)
			if err != nil {
				t.Fatalf("EncodeHeader wrote a PUBLIC_HEADER that DecodeHeader rejects: %v", err)
			}
			if re, err := capsule.EncodeHeader(back); err != nil || !bytes.Equal(re, b) {
				t.Fatal("PUBLIC_HEADER does not re-encode to itself")
			}
		}
		// mode bits 5 and 6: the padding code of the format 2 control, from 0
		// to 3; v2 is its payload_length, possibly above L_MAX.
		for _, format := range []capsule.Format{capsule.Format1, capsule.Format2} {
			c := &capsule.Control{Critical: crit, Noncritical: non}
			if format == capsule.Format2 {
				c.PayloadLength, c.Padding = v2, capsule.Padding(mode>>5&3)
			}
			if b, err := capsule.EncodeControl(c, format); err == nil {
				back, err := capsule.DecodeControl(b, format)
				if err != nil {
					t.Fatalf("EncodeControl wrote a format %d CONTROL_CBOR that DecodeControl rejects: %v", format, err)
				}
				if re, err := capsule.EncodeControl(back, format); err != nil || !bytes.Equal(re, b) {
					t.Fatalf("format %d CONTROL_CBOR does not re-encode to itself", format)
				}
			}
		}
		k := &accesskey.AccessKey{Type: accesskey.TypeX25519, Material: make([]byte, 32), Critical: crit, Noncritical: non}
		var dkk bytes.Buffer
		if err := accesskey.Encode(&dkk, k); err == nil {
			back, err := accesskey.Decode(bytes.NewReader(dkk.Bytes()))
			if err != nil {
				t.Fatalf("accesskey.Encode wrote a .dkk that Decode rejects: %v", err)
			}
			var re bytes.Buffer
			if err := accesskey.Encode(&re, back); err != nil || !bytes.Equal(re.Bytes(), dkk.Bytes()) {
				t.Fatal(".dkk does not re-encode to itself")
			}
		}
	})
}

func hexDecode(s string) ([]byte, error) { return hex.DecodeString(s) }