Initial QSfera import

Server/services/collaboration/pkg/proofkeys/handler.go

@@ -0,0 +1,284 @@
+package proofkeys
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/tls"
+	"encoding/base64"
+	"errors"
+	"math/big"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/beevik/etree"
+	"github.com/rs/zerolog"
+)
+
+type PubKeys struct {
+	Key        *rsa.PublicKey
+	OldKey     *rsa.PublicKey
+	ExpireTime time.Time
+}
+
+type Verifier interface {
+	Verify(accessToken, url, timestamp, sig64, oldSig64 string, opts ...VerifyOption) error
+}
+
+type VerifyHandler struct {
+	discoveryURL string
+	insecure     bool
+	cachedKeys   *PubKeys
+	cachedDur    time.Duration
+}
+
+// NewVerifyHandler will return a new Verifier with the provided parameters
+// The discoveryURL must point to the https://office.wopi/hosting/discovery
+// address, which contains the xml with the proof keys (and more information)
+// The insecure parameter can be used to disable certificate verification when
+// conecting to the provided discoveryURL
+// CachedDur is the duration the keys will be cached in memory. The cached keys
+// will be used for the duration provided, after that new keys will be fetched
+// from the discoveryURL.
+//
+// For WOPI apps whose proof keys rotate after a while, you must ensure that
+// the provided duration is shorter than the rotation time. This should
+// guarantee that we can't fail to verify a request due to obsolete keys.
+func NewVerifyHandler(discoveryURL string, insecure bool, cachedDur time.Duration) Verifier {
+	return &VerifyHandler{
+		discoveryURL: discoveryURL,
+		insecure:     insecure,
+		cachedDur:    cachedDur,
+	}
+}
+
+// Verify the request comes from a trusted source
+// All the provided parameters are strings:
+// * accessToken: The access token used for this request (targeting this collaboration service)
+// * url: The full url for this request, including scheme, host and all query parameters,
+// something like "https://wopi.qsfera.test/wopi/file/abcbcbd?access_token=oiuiu" or
+// "http://wopiserver:8888/wopi/file/abcdef?access_token=zzxxyy"
+// * timestamp: The timestamp provided by the WOPI app in the "X-WOPI-TimeStamp" header, as string
+// * sig64: The base64-encoded signature, which should come directly from the "X-WOPI-Proof" header
+// * oldSig64: The base64-encoded previous signature, coming from the "X-WOPI-ProofOld" header
+//
+// The public keys will be obtained from the /hosting/discovery path of the target WOPI app.
+// Note that the method will perform the following checks in that order:
+// * current signature with the current key
+// * old signature with the current key
+// * current signature with the old key
+// If all of those checks are wrong, the method will fail, and the request should be rejected.
+//
+// The method will return an error if something fails, or nil if everything is ok
+func (vh *VerifyHandler) Verify(accessToken, url, timestamp, sig64, oldSig64 string, opts ...VerifyOption) error {
+	verifyOptions := newOptions(opts...)
+
+	// check timestamp
+	if err := vh.checkTimestamp(timestamp); err != nil {
+		return err
+	}
+
+	// need to decode the signatures
+	signature, err := base64.StdEncoding.DecodeString(sig64)
+	if err != nil {
+		return err
+	}
+
+	var oldSignature []byte
+	if oldSig64 != "" {
+		if oldSig, err := base64.StdEncoding.DecodeString(oldSig64); err != nil {
+			return err
+		} else {
+			oldSignature = oldSig
+		}
+	}
+
+	pubkeys := vh.cachedKeys
+	if pubkeys == nil || pubkeys.ExpireTime.Before(time.Now()) {
+		// fetch the public keys
+		newpubkeys, err := vh.fetchPublicKeys(verifyOptions.Logger)
+		if err != nil {
+			return err
+		}
+		pubkeys = newpubkeys
+		vh.cachedKeys = newpubkeys
+	}
+
+	// build and hash the expected proof
+	expectedProof := vh.generateProof(accessToken, url, timestamp)
+	hashedProof := sha256.Sum256(expectedProof)
+
+	// verify
+	if err := rsa.VerifyPKCS1v15(pubkeys.Key, crypto.SHA256, hashedProof[:], signature); err != nil {
+		if err := rsa.VerifyPKCS1v15(pubkeys.Key, crypto.SHA256, hashedProof[:], oldSignature); err != nil {
+			if pubkeys.OldKey != nil {
+				return rsa.VerifyPKCS1v15(pubkeys.OldKey, crypto.SHA256, hashedProof[:], signature)
+			} else {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// checkTimestamp will check if the provided timestamp is valid.
+// The timestamp is valid if it isn't older than 20 minutes (info from
+// MS WOPI docs).
+//
+// Note: the timestamp is based on C# DateTime.UtcNow.Ticks
+// "One tick equals 100 nanoseconds. The value of this property represents
+// the number of ticks that have elapsed since 12:00:00 midnight, January 1, 0001."
+// It is NOT a unix timestamp (current unix timestamp ~1718123417 secs ;
+// expected timestamp ~638537195321890000 100-nanosecs)
+func (vh *VerifyHandler) checkTimestamp(timestamp string) error {
+	// set the stamp
+	stamp, err := strconv.ParseInt(timestamp, 10, 64)
+	if err != nil {
+		return errors.New("Invalid timestamp")
+	}
+
+	// 62135596800 seconds from "January 1, 1 AD" to "January 1, 1970 12:00:00 AM"
+	// need to convert those secs into 100-nanosecs in order to compare the stamp
+	unixBaseStamp := int64(62135596800 * 1000 * 1000 * 10)
+
+	// stamp - unixBaseStamp gives us the unix-based timestamp we can use
+	unixStamp := stamp - unixBaseStamp
+
+	// divide between 1000*1000*10 to get the seconds and 100-nanoseconds
+	unixStampSec := unixStamp / (1000 * 1000 * 10)
+	unixStampNanoSec := (unixStamp % (1000 * 1000 * 10)) * 100
+
+	// both seconds and nanoseconds should be within int64 range
+	convertedUnixTimestamp := time.Unix(unixStampSec, unixStampNanoSec)
+
+	if time.Now().After(convertedUnixTimestamp.Add(20 * time.Minute)) {
+		return errors.New("Timestamp expired")
+	}
+	return nil
+}
+
+// generateProof will generated a expected proof to be verified later.
+// The method will return a slice of bytes with the proof (consider it binary
+// data).
+// The bytes will need to be hashed later in order to perform the verification
+func (vh *VerifyHandler) generateProof(accessToken, url, timestamp string) []byte {
+	tokenBytes := []byte(accessToken)
+	tokenLen := len(tokenBytes)
+	tokenLenBytes := big.NewInt(int64(tokenLen)).FillBytes(make([]byte, 4))
+
+	// url needs to be uppercase
+	urlBytes := []byte(strings.ToUpper(url))
+	urlLen := len(urlBytes)
+	urlLenBytes := big.NewInt(int64(urlLen)).FillBytes(make([]byte, 4))
+
+	stampBigInt, _ := new(big.Int).SetString(timestamp, 10)
+	stampBytes := stampBigInt.FillBytes(make([]byte, 8))
+	stampLen := len(stampBytes)
+	stampLenBytes := big.NewInt(int64(stampLen)).FillBytes(make([]byte, 4))
+
+	proof := new(bytes.Buffer)
+	proof.Write(tokenLenBytes)
+	proof.Write(tokenBytes)
+	proof.Write(urlLenBytes)
+	proof.Write(urlBytes)
+	proof.Write(stampLenBytes)
+	proof.Write(stampBytes)
+	return proof.Bytes()
+}
+
+// fetchPublicKeys will fetch the public keys from the /hosting/discovery URL
+// of the provided WOPI app.
+// It will return a PubKeys struct to hold the public keys based on the modulus
+// and exponent found.
+// The PubKeys returned might be either nil (with the non-nil error), or might
+// contain only a PubKeys.Key field (the PubKeys.OldKey might be nil)
+func (vh *VerifyHandler) fetchPublicKeys(logger *zerolog.Logger) (*PubKeys, error) {
+	logger.Debug().Str("WopiAppUrl", vh.discoveryURL).Msg("WopiDiscovery: requesting new public keys")
+
+	httpClient := http.Client{
+		Transport: &http.Transport{
+			TLSClientConfig: &tls.Config{
+				MinVersion:         tls.VersionTLS12,
+				InsecureSkipVerify: vh.insecure,
+			},
+		},
+	}
+
+	httpResp, err := httpClient.Get(vh.discoveryURL)
+	if err != nil {
+		logger.Error().
+			Err(err).
+			Str("WopiAppUrl", vh.discoveryURL).
+			Msg("WopiDiscovery: failed to access wopi app url")
+		return nil, err
+	}
+
+	defer httpResp.Body.Close()
+
+	if httpResp.StatusCode != http.StatusOK {
+		logger.Error().
+			Str("WopiAppUrl", vh.discoveryURL).
+			Int("HttpCode", httpResp.StatusCode).
+			Msg("WopiDiscovery: wopi app url failed with unexpected code")
+		return nil, errors.New("wopi app url failed with unexpected code")
+	}
+
+	doc := etree.NewDocument()
+	if _, err := doc.ReadFrom(httpResp.Body); err != nil {
+		return nil, err
+	}
+
+	root := doc.SelectElement("wopi-discovery")
+	if root == nil {
+		return nil, errors.New("wopi-discovery element not found in the XML body")
+	}
+
+	proofKey := root.SelectElement("proof-key")
+	if proofKey == nil {
+		return nil, errors.New("proof-key element not found in the XML body")
+	}
+
+	mod64 := proofKey.SelectAttrValue("modulus", "")
+	exp64 := proofKey.SelectAttrValue("exponent", "")
+	oldMod64 := proofKey.SelectAttrValue("oldmodulus", "")
+	oldExp64 := proofKey.SelectAttrValue("oldexponent", "")
+
+	if mod64 == "" || exp64 == "" {
+		return nil, errors.New("modulus or exponent not found in the proof-key element")
+	}
+
+	keys := &PubKeys{
+		Key:        vh.keyFromBase64(mod64, exp64),
+		ExpireTime: time.Now().Add(vh.cachedDur),
+	}
+
+	if oldMod64 != "" && oldExp64 != "" {
+		keys.OldKey = vh.keyFromBase64(oldMod64, oldExp64)
+	}
+
+	return keys, nil
+}
+
+// keyFromBase64 will create a rsa public key from the provided modulus and
+// exponent, both encoded with base64.
+// If any of the provided strings can't be decoded, nil will be returned.
+func (vh *VerifyHandler) keyFromBase64(mod64, exp64 string) *rsa.PublicKey {
+	dataMod, err := base64.StdEncoding.DecodeString(mod64)
+	if err != nil {
+		return nil
+	}
+
+	dataE, err := base64.StdEncoding.DecodeString(exp64)
+	if err != nil {
+		return nil
+	}
+
+	pub := &rsa.PublicKey{
+		N: new(big.Int).SetBytes(dataMod),
+		E: int(new(big.Int).SetBytes(dataE).Int64()),
+	}
+	return pub
+}