combine.go

// Copyright 2020 Anapaya Systems
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package trcs

import (
	"bytes"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"os"
	"sort"

	"github.com/google/go-cmp/cmp"
	"github.com/spf13/cobra"

	"github.com/scionproto/scion/pkg/private/serrors"
	"github.com/scionproto/scion/pkg/scrypto/cms/protocol"
	"github.com/scionproto/scion/pkg/scrypto/cppki"
	"github.com/scionproto/scion/private/app/command"
)

func newCombine(pather command.Pather) *cobra.Command {
	var flags struct {
		out     string
		payload string
		format  string
	}

	cmd := &cobra.Command{
		Use:   "combine",
		Short: "Combine partially signed TRCs",
		Long: `'combine' combines the signatures on partially signed TRCs into one single TRC.
The command checks that all parts sign the same TRC payload content.

No further checks are made. Check that the TRC is valid and verifiable with the
appropriate commands.
`,
		Example: fmt.Sprintf(`  %[1]s combine --payload ISD1-B1-S1.pld -o ISD1-B1-S1.trc `+
			`ISD1-B1-S1.org1 ISD1-B1-S1.org2`, pather.CommandPath()),
		Args: cobra.MinimumNArgs(1),
		RunE: func(cmd *cobra.Command, args []string) error {
			cmd.SilenceUsage = true
			return RunCombine(args, flags.payload, flags.out, flags.format)
		},
	}

	addOutputFlag(&flags.out, cmd)
	cmd.Flags().StringVarP(&flags.payload, "payload", "p", "",
		"The TRC payload. If provided, it will be used as a reference payload to compare the "+
			"partially signed TRC payloads against. It can be either DER or PEM encoded.")
	cmd.Flags().StringVar(&flags.format, "format", "der", "Output format (der|pem)")

	return cmd
}

// RunCombine combines the partially signed TRC files and writes them to
// the out directory, pld is the payload file.
func RunCombine(files []string, pld, out string, format string) error {
	trcs := make(map[string]cppki.SignedTRC)
	for _, name := range files {
		dec, err := DecodeFromFile(name)
		if err != nil {
			return serrors.WrapStr("error decoding part", err, "file", name)
		}
		trcs[name] = dec
	}
	if err := verifyPayload(pld, trcs); err != nil {
		return err
	}
	packed, err := CombineSignedPayloads(trcs)
	if err != nil {
		return err
	}
	if format == "pem" {
		packed = pem.EncodeToMemory(&pem.Block{
			Type:  "TRC",
			Bytes: packed,
		})
	}
	if err := os.WriteFile(out, packed, 0644); err != nil {
		return serrors.WrapStr("error writing combined TRC", err)
	}
	fmt.Printf("Successfully combined TRC at %s\n", out)
	return nil
}

// CombineSignedPayloads combines the signed TRC payloads and checks that all payloads and
// signer infos are consistent.
func CombineSignedPayloads(trcs map[string]cppki.SignedTRC) ([]byte, error) {
	if err := verifyPayload("", trcs); err != nil {
		return nil, err
	}
	infos, err := combineSignerInfos(trcs)
	if err != nil {
		return nil, err
	}
	// Extract any payload. They are guaranteed to be the same
	var pld []byte
	for _, signed := range trcs {
		pld = signed.TRC.Raw
		break
	}
	eci, err := protocol.NewDataEncapsulatedContentInfo(pld)
	if err != nil {
		return nil, serrors.WrapStr("error encoding payload", err)
	}
	sd := protocol.SignedData{
		Version:          1,
		EncapContentInfo: eci,
		SignerInfos:      infos,
		DigestAlgorithms: combineDigestAlgorithms(infos),
	}
	// Write signed TRC.
	packed, err := sd.ContentInfoDER()
	if err != nil {
		return nil, serrors.WrapStr("error packing combined TRC", err)
	}
	return packed, nil
}

// combineSignerInfos combines all singer infos. It checks that non-unique
// signer infos are equal. The returned slice is sorted.
func combineSignerInfos(trcs map[string]cppki.SignedTRC) ([]protocol.SignerInfo, error) {
	type SignerOrigin struct {
		Info protocol.SignerInfo
		File string
	}
	var errs serrors.List
	infos := make(map[string]SignerOrigin)
	for name, signed := range trcs {
		for _, si := range signed.SignerInfos {
			sid := string(si.SID.FullBytes)
			existing, ok := infos[sid]
			if !ok {
				infos[sid] = SignerOrigin{
					Info: si,
					File: name,
				}
				continue
			}
			if !cmp.Equal(si, existing.Info) {
				errs = append(errs, serrors.New("different SignerInfo contents for same subject",
					"files", []string{name, existing.File}))
			}
		}
	}
	if err := errs.ToError(); err != nil {
		return nil, err
	}
	var l []protocol.SignerInfo
	for _, info := range infos {
		l = append(l, info.Info)
	}
	// Keep sorting for consistent output for older go versions.
	// Starting from go1.15, the SignerInfos will be sorted when serializing.
	sort.Slice(l, func(i, j int) bool {
		return bytes.Compare(l[i].SID.FullBytes, l[j].SID.FullBytes) < 0
	})
	return l, nil
}

func combineDigestAlgorithms(infos []protocol.SignerInfo) []pkix.AlgorithmIdentifier {
	var algos []pkix.AlgorithmIdentifier
	for _, si := range infos {
		if !findDigestAlgorithm(si.DigestAlgorithm, algos) {
			algos = append(algos, si.DigestAlgorithm)
		}
	}
	sort.Slice(algos, func(i, j int) bool {
		return algos[i].Algorithm.String() < algos[j].Algorithm.String()
	})
	return algos
}

func findDigestAlgorithm(algo pkix.AlgorithmIdentifier, algos []pkix.AlgorithmIdentifier) bool {
	for _, existing := range algos {
		if existing.Algorithm.Equal(algo.Algorithm) {
			return bytes.Equal(existing.Parameters.FullBytes, algo.Parameters.FullBytes)
		}
	}
	return false
}

func verifyPayload(pld string, trcs map[string]cppki.SignedTRC) error {
	var errs serrors.List
	var rawPld []byte
	if pld != "" {
		var err error
		rawPld, err = os.ReadFile(pld)
		if err != nil {
			return serrors.WrapStr("error loading payload", err)
		}
		block, _ := pem.Decode(rawPld)
		if block != nil && block.Type == "TRC PAYLOAD" {
			rawPld = block.Bytes
		}
	}
	for name, signed := range trcs {
		if rawPld == nil {
			rawPld = signed.TRC.Raw
			continue
		}
		if !bytes.Equal(signed.TRC.Raw, rawPld) {
			errs = append(errs, serrors.New("different payload contents", "file", name))
		}
	}

	return errs.ToError()
}