Implement latest draft-ietf-acme-ari spec (#461)

The draft spec version at the time of this PR was
draft-ietf-acme-ari-03, but failed replacement order handling is from
the [yet-to-be-released
draft-ietf-acme-ari-04](https://github.com/aarongable/draft-acme-ari/blob/1813de294a6d813f4eba3f5c45b14ee5139ef66a/draft-ietf-acme-ari.md#L177).

* Add a `renewalInfo` entry to the directory object which provides the
base URL for ARI requests.
* Add a new WFE handlefunc which parses incoming requests and returns
reasonable `renewalInfo` for determining when the client should attempt
renewal of a certificate.
* Add support for marking orders as `replaced`. Replacement orders can
be chained, but there can be no duplicate replacement of orders, just
like boulder.
* Restructured the asynchronous finalization anonymous go func to handle
storing replaced orders. To be replaced, an order must previously have
been finalized and have an issued certificate.

acme/common.go

@@ -59,6 +59,9 @@ type Order struct {
 	NotAfter       string          `json:"notAfter,omitempty"`
 	Authorizations []string        `json:"authorizations"`
 	Certificate    string          `json:"certificate,omitempty"`
+
+	// https://datatracker.ietf.org/doc/html/draft-ietf-acme-ari-03#section-5
+	Replaces string `json:"replaces,omitempty"`
 }
 
 // An Authorization is created for each identifier in an order

ca/ca.go

@@ -438,6 +438,25 @@ func (ca *CAImpl) CompleteOrder(order *core.Order) {
 	order.Unlock()
 }
 
+// RecognizedSKID attempts to match the incoming Authority Key Idenfitier (AKID)
+// bytes to the Subject Key Identifier (SKID) of an intermediate certificate. It
+// returns an error if no match is found.
+func (ca *CAImpl) RecognizedSKID(issuer []byte) error {
+	if issuer == nil {
+		return errors.New("issuer bytes must not be nil")
+	}
+
+	for _, chain := range ca.chains {
+		for _, intermediate := range chain.intermediates {
+			if bytes.Equal(intermediate.cert.Cert.SubjectKeyId, issuer) {
+				return nil
+			}
+		}
+	}
+
+	return errors.New("no known issuer matches the provided Authority Key Identifier ")
+}
+
 func (ca *CAImpl) GetNumberOfRootCerts() int {
 	return len(ca.chains)
 }

cmd/pebble/main.go

@@ -95,7 +95,7 @@ func main() {
 
 	db := db.NewMemoryStore()
 	ca := ca.New(logger, db, c.Pebble.OCSPResponderURL, alternateRoots, chainLength, c.Pebble.CertificateValidityPeriod)
-	va := va.New(logger, c.Pebble.HTTPPort, c.Pebble.TLSPort, *strictMode, *resolverAddress)
+	va := va.New(logger, c.Pebble.HTTPPort, c.Pebble.TLSPort, *strictMode, *resolverAddress, db)
 
 	for keyID, key := range c.Pebble.ExternalAccountMACKeys {
 		err := db.AddExternalAccountKeyByID(keyID, key)

core/types.go

@@ -5,9 +5,11 @@ import (
 	"crypto"
 	"crypto/x509"
 	"encoding/base64"
+	"encoding/hex"
 	"encoding/pem"
 	"errors"
 	"fmt"
+	"math/big"
 	"sync"
 	"time"
 
@@ -27,6 +29,8 @@ type Order struct {
 	AuthorizationObjects []*Authorization
 	BeganProcessing      bool
 	CertificateObject    *Certificate
+	// Indicates if the finalized order has been successfully replaced via ARI.
+	IsReplaced bool
 }
 
 func (o *Order) GetStatus() (string, error) {
@@ -200,3 +204,85 @@ type ValidationRecord struct {
 	Error       *acme.ProblemDetails
 	ValidatedAt time.Time
 }
+
+// CertID represents a unique identifier (CertID) for a certificate as per the
+// ACME protocol's "renewalInfo" resource, as specified in draft-ietf-acme-ari-
+// 03. The CertID is a composite string derived from the base64url-encoded
+// keyIdentifier of the certificate's Authority Key Identifier (AKI) and the
+// base64url-encoded serial number of the certificate, separated by a period.
+// For more details see:
+// https://datatracker.ietf.org/doc/html/draft-ietf-acme-ari-02#section-4.1.
+type CertID struct {
+	KeyIdentifier []byte
+	SerialNumber  *big.Int
+	// id is the pre-computed hex encoding of SerialNumber.
+	id string
+}
+
+// SerialHex returns a CertID's id field.
+func (c CertID) SerialHex() string {
+	return c.id
+}
+
+// NewCertID takes bytes representing a serial number and authority key
+// identifier and returns a CertID or an error.
+func NewCertID(serial []byte, akid []byte) (*CertID, error) {
+	if serial == nil || akid == nil {
+		return nil, errors.New("must send non-nil bytes")
+	}
+
+	return &CertID{
+		KeyIdentifier: akid,
+		SerialNumber:  new(big.Int).SetBytes(serial),
+		id:            hex.EncodeToString(serial),
+	}, nil
+}
+
+// SuggestedWindow is a type exposed inside the RenewalInfo resource.
+type SuggestedWindow struct {
+	Start time.Time `json:"start"`
+	End   time.Time `json:"end"`
+}
+
+// IsWithin returns true if the given time is within the suggested window,
+// inclusive of the start time and exclusive of the end time.
+func (window SuggestedWindow) IsWithin(now time.Time) bool {
+	return !now.Before(window.Start) && now.Before(window.End)
+}
+
+// RenewalInfo is a type which is exposed to clients which query the renewalInfo
+// endpoint specified in draft-aaron-ari.
+type RenewalInfo struct {
+	SuggestedWindow SuggestedWindow `json:"suggestedWindow"`
+}
+
+// RenewalInfoSimple constructs a `RenewalInfo` object and suggested window
+// using a very simple renewal calculation: calculate a point 2/3rds of the way
+// through the validity period, then give a 2-day window around that. Both the
+// `issued` and `expires` timestamps are expected to be UTC.
+func RenewalInfoSimple(issued time.Time, expires time.Time) *RenewalInfo {
+	validity := expires.Add(time.Second).Sub(issued)
+	renewalOffset := validity / time.Duration(3)
+	idealRenewal := expires.Add(-renewalOffset)
+	return &RenewalInfo{
+		SuggestedWindow: SuggestedWindow{
+			Start: idealRenewal.Add(-24 * time.Hour),
+			End:   idealRenewal.Add(24 * time.Hour),
+		},
+	}
+}
+
+// RenewalInfoImmediate constructs a `RenewalInfo` object with a suggested
+// window in the past. Per the draft-ietf-acme-ari-01 spec, clients should
+// attempt to renew immediately if the suggested window is in the past. The
+// passed `now` is assumed to be a timestamp representing the current moment in
+// time.
+func RenewalInfoImmediate(now time.Time) *RenewalInfo {
+	oneHourAgo := now.Add(-1 * time.Hour)
+	return &RenewalInfo{
+		SuggestedWindow: SuggestedWindow{
+			Start: oneHourAgo,
+			End:   oneHourAgo.Add(time.Minute * 30),
+		},
+	}
+}

db/memorystore.go

@@ -46,8 +46,11 @@ type MemoryStore struct {
 	// key bytes.
 	accountsByKeyID map[string]*core.Account
 
-	ordersByID        map[string]*core.Order
-	ordersByAccountID map[string][]*core.Order
+	// ordersByIssuedSerial indexes the hex encoding of the certificate's
+	// SerialNumber.
+	ordersByIssuedSerial map[string]*core.Order
+	ordersByID           map[string]*core.Order
+	ordersByAccountID    map[string][]*core.Order
 
 	authorizationsByID map[string]*core.Authorization
 
@@ -66,6 +69,7 @@ func NewMemoryStore() *MemoryStore {
 		accountRand:             rand.New(rand.NewSource(time.Now().UnixNano())),
 		accountsByID:            make(map[string]*core.Account),
 		accountsByKeyID:         make(map[string]*core.Account),
+		ordersByIssuedSerial:    make(map[string]*core.Order),
 		ordersByID:              make(map[string]*core.Order),
 		ordersByAccountID:       make(map[string][]*core.Order),
 		authorizationsByID:      make(map[string]*core.Authorization),
@@ -94,6 +98,28 @@ func (m *MemoryStore) GetAccountByKey(key crypto.PublicKey) (*core.Account, erro
 	return m.accountsByKeyID[keyID], nil
 }
 
+// UpdateReplacedOrder takes a serial and marks a parent order as
+// replaced/not-replaced or returns an error.
+//
+// We intentionally don't Lock the database inside this method because the inner
+// GetOrderByIssuedSerial which is used elsewhere does an RLock which would
+// hang.
+func (m *MemoryStore) UpdateReplacedOrder(serial string, shouldBeReplaced bool) error {
+	if serial == "" {
+		return acme.InternalErrorProblem("no serial provided")
+	}
+
+	originalOrder, err := m.GetOrderByIssuedSerial(serial)
+	if err != nil {
+		return acme.InternalErrorProblem(fmt.Sprintf("could not find an order for the given certificate: %s", err))
+	}
+	originalOrder.Lock()
+	defer originalOrder.Unlock()
+	originalOrder.IsReplaced = shouldBeReplaced
+
+	return nil
+}
+
 // Note that this function should *NOT* be used for key changes. It assumes
 // the public key associated to the account does not change. Use ChangeAccountKey
 // to change the account's public key.
@@ -195,6 +221,19 @@ func (m *MemoryStore) AddOrder(order *core.Order) (int, error) {
 	return len(m.ordersByID), nil
 }
 
+func (m *MemoryStore) AddOrderByIssuedSerial(order *core.Order) error {
+	m.Lock()
+	defer m.Unlock()
+
+	if order.CertificateObject == nil {
+		return errors.New("order must have non-empty CertificateObject")
+	}
+
+	m.ordersByIssuedSerial[order.CertificateObject.ID] = order
+
+	return nil
+}
+
 func (m *MemoryStore) GetOrderByID(id string) *core.Order {
 	m.RLock()
 	defer m.RUnlock()
@@ -212,6 +251,20 @@ func (m *MemoryStore) GetOrderByID(id string) *core.Order {
 	return nil
 }
 
+// GetOrderByIssuedSerial returns the order that resulted in the given certificate
+// serial. If no such order exists, an error will be returned.
+func (m *MemoryStore) GetOrderByIssuedSerial(serial string) (*core.Order, error) {
+	m.RLock()
+	defer m.RUnlock()
+
+	order, ok := m.ordersByIssuedSerial[serial]
+	if !ok {
+		return nil, errors.New("could not find order resulting in the given certificate serial number")
+	}
+
+	return order, nil
+}
+
 func (m *MemoryStore) GetOrdersByAccountID(accountID string) []*core.Order {
 	m.RLock()
 	defer m.RUnlock()

va/va.go

@@ -27,6 +27,7 @@ import (
 	"github.com/letsencrypt/challtestsrv"
 	"github.com/letsencrypt/pebble/v2/acme"
 	"github.com/letsencrypt/pebble/v2/core"
+	"github.com/letsencrypt/pebble/v2/db"
 )
 
 const (
@@ -108,12 +109,18 @@ type VAImpl struct {
 	strict             bool
 	customResolverAddr string
 	dnsClient          *dns.Client
+
+	// The VA having a DB client is indeed strange. This is only used to
+	// facilitate va.setOrderError changing the ARI related order replacement
+	// field on failed orders.
+	db *db.MemoryStore
 }
 
 func New(
 	log *log.Logger,
 	httpPort, tlsPort int,
 	strict bool, customResolverAddr string,
+	db *db.MemoryStore,
 ) *VAImpl {
 	va := &VAImpl{
 		log:                log,
@@ -124,6 +131,7 @@ func New(
 		sleepTime:          defaultSleepTime,
 		strict:             strict,
 		customResolverAddr: customResolverAddr,
+		db:                 db,
 	}
 
 	if customResolverAddr != "" {
@@ -209,10 +217,17 @@ func (va VAImpl) setAuthzValid(authz *core.Authorization, chal *core.Challenge)
 
 // setOrderError updates an order with an error from an authorization
 // validation.
-func (va VAImpl) setOrderError(order *core.Order, err *acme.ProblemDetails) {
+func (va VAImpl) setOrderError(order *core.Order, prob *acme.ProblemDetails) {
 	order.Lock()
 	defer order.Unlock()
-	order.Error = err
+	order.Error = prob
+
+	// Mark the parent order as "not replaced yet" so a new replacement order
+	// can be attempted.
+	err := va.db.UpdateReplacedOrder(order.Replaces, false)
+	if err != nil {
+		va.log.Printf("Error updating replacement order: %s", err)
+	}
 }
 
 // setAuthzInvalid updates an authorization and an associated challenge to be

va/va_test.go

@@ -31,7 +31,7 @@ func TestAuthzRace(_ *testing.T) {
 
 	// This whole test can be removed if/when the MemoryStore becomes 100% by value
 	ms := db.NewMemoryStore()
-	va := New(log.New(os.Stdout, "Pebble/TestRace", log.LstdFlags), 14000, 15000, false, "")
+	va := New(log.New(os.Stdout, "Pebble/TestRace", log.LstdFlags), 14000, 15000, false, "", ms)
 
 	authz := &core.Authorization{
 		ID: "auth-id",