nuts-foundation/nuts-node

/*
 * Copyright (C) 2021 Nuts community
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 */

package dag

import (
    "context"
    "crypto"
    "errors"
    "fmt"
    "time"

    "github.com/lestrrat-go/jwx/v2/jwk"
    "github.com/lestrrat-go/jwx/v2/jws"
    nutsCrypto "github.com/nuts-foundation/nuts-node/crypto"
)

const errSigningTransactionFmt = "error while signing transaction: %w"

// TransactionSigner defines functions to sign transactions.
type TransactionSigner interface {
    // Sign signs the unsigned transaction, including the signingTime parameter as header.
    Sign(ctx context.Context, input UnsignedTransaction, signingTime time.Time) (Transaction, error)
}

// NewTransactionSigner creates a TransactionSigner that signs the transaction using the given key.
// The public key is included in the signed transaction when given. If not, the `kid` header is added which refers to the ID
// of the used key.
func NewTransactionSigner(signer nutsCrypto.JWTSigner, kid string, key crypto.PublicKey) TransactionSigner {
    return &transactionSigner{
        key:    key,
        kid:    kid,
        signer: signer,
    }
}

type transactionSigner struct {
    kid    string
    key    crypto.PublicKey
    signer nutsCrypto.JWTSigner
}

func (d transactionSigner) Sign(ctx context.Context, input UnsignedTransaction, signingTime time.Time) (Transaction, error) {
    // Preliminary sanity checks
    if signingTime.IsZero() {
        return nil, errors.New("signing time is zero")
    }
    if tx, ok := input.(Transaction); ok && !tx.SigningTime().IsZero() {
        return nil, errors.New("transaction is already signed")
    }

    var key jwk.Key
    var err error
    if d.key != nil {
        key, err = jwk.FromRaw(d.key)
        if err != nil {
            return nil, fmt.Errorf(errSigningTransactionFmt, err)
        }
        _ = key.Set(jwk.KeyIDKey, d.kid)
    }

    prevsAsString := make([]string, len(input.Previous()))
    for i, prev := range input.Previous() {
        prevsAsString[i] = prev.String()
    }
    normalizedMoment := signingTime.UTC()
    headerMap := map[string]interface{}{
        jws.ContentTypeKey: input.PayloadType(),
        jws.CriticalKey:    []string{signingTimeHeader, versionHeader, previousHeader, lamportClockHeader},
        signingTimeHeader:  normalizedMoment.Unix(),
        previousHeader:     prevsAsString,
        versionHeader:      input.Version(),
        lamportClockHeader: input.Clock(),
    }

    if input.PAL() != nil {
        headerMap[palHeader] = input.PAL()
    }

    if d.key != nil {
        headerMap[jws.JWKKey] = key
    } else {
        headerMap[jws.KeyIDKey] = d.kid
    }
    data, err := d.signer.SignJWS(ctx, []byte(input.PayloadHash().String()), headerMap, d.kid, false)
    if err != nil {
        return nil, fmt.Errorf(errSigningTransactionFmt, err)
    }
    signedTransaction, err := ParseTransaction([]byte(data))
    if err != nil {
        return nil, fmt.Errorf(errSigningTransactionFmt, err)
    }
    return signedTransaction, nil
}