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team_ek.go
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team_ek.go
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package ephemeral
import (
"context"
"encoding/json"
"fmt"
"github.com/keybase/client/go/libkb"
"github.com/keybase/client/go/protocol/keybase1"
"github.com/keybase/client/go/teams"
)
type TeamEKSeed keybase1.Bytes32
func newTeamEphemeralSeed() (seed TeamEKSeed, err error) {
randomSeed, err := makeNewRandomSeed()
if err != nil {
return seed, err
}
return TeamEKSeed(randomSeed), nil
}
func newTeamEKSeedFromBytes(b []byte) (s TeamEKSeed, err error) {
seed, err := newEKSeedFromBytes(b)
if err != nil {
return s, err
}
return TeamEKSeed(seed), nil
}
func (s *TeamEKSeed) DeriveDHKey() *libkb.NaclDHKeyPair {
return deriveDHKey(keybase1.Bytes32(*s), libkb.DeriveReasonTeamEKEncryption)
}
func postNewTeamEK(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID, sig string, boxes *[]keybase1.TeamEkBoxMetadata) (err error) {
defer g.CTraceTimed(ctx, "postNewTeamEK", func() error { return err })()
boxesJSON, err := json.Marshal(*boxes)
if err != nil {
return err
}
apiArg := libkb.APIArg{
Endpoint: "team/team_ek",
SessionType: libkb.APISessionTypeREQUIRED,
NetContext: ctx,
Args: libkb.HTTPArgs{
"team_id": libkb.S{Val: string(teamID)},
"sig": libkb.S{Val: sig},
"boxes": libkb.S{Val: string(boxesJSON)},
},
}
_, err = g.GetAPI().Post(apiArg)
return err
}
func prepareNewTeamEK(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID, signingKey libkb.NaclSigningKeyPair, membersMetadata map[keybase1.UID]keybase1.UserEkMetadata, merkleRoot libkb.MerkleRoot) (sig string, boxes *[]keybase1.TeamEkBoxMetadata, metadata keybase1.TeamEkMetadata, myBox *keybase1.TeamEkBoxed, err error) {
defer g.CTraceTimed(ctx, "prepareNewTeamEK", func() error { return err })()
seed, err := newTeamEphemeralSeed()
if err != nil {
return "", nil, metadata, nil, err
}
prevStatement, latestGeneration, wrongKID, err := fetchTeamEKStatement(ctx, g, teamID)
if !wrongKID && err != nil {
return "", nil, metadata, nil, err
}
var generation keybase1.EkGeneration
if prevStatement == nil {
// Even if the teamEK statement was signed by the wrong key (this can
// happen when legacy clients roll the PTK), fetchTeamEKStatement will
// return the generation number from the last (unverifiable) statement.
// If there was never any statement, latestGeneration will be 0, so
// adding one is correct in all cases.
generation = latestGeneration + 1
} else {
generation = prevStatement.CurrentTeamEkMetadata.Generation + 1
}
dhKeypair := seed.DeriveDHKey()
metadata = keybase1.TeamEkMetadata{
Kid: dhKeypair.GetKID(),
Generation: generation,
HashMeta: merkleRoot.HashMeta(),
// The ctime is derivable from the hash meta, by fetching the hashed
// root from the server, but including it saves readers a potential
// extra round trip.
Ctime: keybase1.TimeFromSeconds(merkleRoot.Ctime()),
}
// Get the list of existing teamEKs to form the full statement. Make sure
// that if it's nil, we replace it with an empty slice. Although those are
// practically the same in Go, they get serialized to different JSON.
existingActiveMetadata, err := filterStaleTeamEKStatement(ctx, g, prevStatement, merkleRoot)
if err != nil {
return "", nil, metadata, nil, err
}
if existingActiveMetadata == nil {
existingActiveMetadata = []keybase1.TeamEkMetadata{}
}
statement := keybase1.TeamEkStatement{
CurrentTeamEkMetadata: metadata,
ExistingTeamEkMetadata: existingActiveMetadata,
}
statementJSON, err := json.Marshal(statement)
if err != nil {
return "", nil, metadata, nil, err
}
sig, _, err = signingKey.SignToString(statementJSON)
if err != nil {
return "", nil, metadata, nil, err
}
teamEK := keybase1.TeamEk{
Seed: keybase1.Bytes32(seed),
Metadata: metadata,
}
boxes, myTeamEKBoxed, err := boxTeamEKForUsers(ctx, g, membersMetadata, teamEK)
if err != nil {
return "", nil, metadata, nil, err
}
return sig, boxes, metadata, myTeamEKBoxed, nil
}
func publishNewTeamEK(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID, merkleRoot libkb.MerkleRoot) (metadata keybase1.TeamEkMetadata, err error) {
defer g.CTraceTimed(ctx, "publishNewTeamEK", func() error { return err })()
team, err := teams.Load(ctx, g, keybase1.LoadTeamArg{
ID: teamID,
})
if err != nil {
return metadata, err
}
signingKey, err := team.SigningKey()
if err != nil {
return metadata, err
}
statementMap, err := fetchTeamMemberStatements(ctx, g, teamID)
if err != nil {
return metadata, err
}
membersMetadata, err := activeUserEKMetadata(ctx, g, statementMap, merkleRoot)
if err != nil {
return metadata, err
}
sig, boxes, metadata, myBox, err := prepareNewTeamEK(ctx, g, teamID, signingKey, membersMetadata, merkleRoot)
if err != nil {
return metadata, err
}
err = postNewTeamEK(ctx, g, teamID, sig, boxes)
if err != nil {
return metadata, err
}
if myBox == nil {
g.Log.CDebugf(ctx, "No box made for own teamEK")
} else {
storage := g.GetTeamEKBoxStorage()
err = storage.Put(ctx, teamID, metadata.Generation, *myBox)
if err != nil {
return metadata, err
}
}
return metadata, nil
}
// There are plenty of race conditions where the PTK or teamEK or
// membership list can change out from under us while we're in the middle
// of posting a new key, causing the post to fail. Detect these conditions
// and retry.
func teamEKRetryWrapper(ctx context.Context, g *libkb.GlobalContext, retryFn func() error) (err error) {
tries := 0
maxTries := 3
knownRaceConditions := []keybase1.StatusCode{
keybase1.StatusCode_SCSigWrongKey,
keybase1.StatusCode_SCSigOldSeqno,
keybase1.StatusCode_SCEphemeralKeyBadGeneration,
keybase1.StatusCode_SCEphemeralKeyUnexpectedBox,
keybase1.StatusCode_SCEphemeralKeyMissingBox,
keybase1.StatusCode_SCEphemeralKeyWrongNumberOfKeys,
}
for {
tries++
err = retryFn()
if err != nil {
retryableError := false
for _, code := range knownRaceConditions {
if libkb.IsAppStatusCode(err, code) {
g.Log.CDebugf(ctx, "teamEKRetryWrapper found a retryable error on try %d: %s", tries, err)
retryableError = true
break
}
}
if !retryableError || tries >= maxTries {
return err
}
} else {
return nil
}
}
}
func ForcePublishNewTeamEKForTesting(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID, merkleRoot libkb.MerkleRoot) (metadata keybase1.TeamEkMetadata, err error) {
defer g.CTraceTimed(ctx, "ForcePublishNewTeamEKForTesting", func() error { return err })()
err = teamEKRetryWrapper(ctx, g, func() error {
metadata, err = publishNewTeamEK(ctx, g, teamID, merkleRoot)
return err
})
return metadata, err
}
func boxTeamEKForUsers(ctx context.Context, g *libkb.GlobalContext, usersMetadata map[keybase1.UID]keybase1.UserEkMetadata, teamEK keybase1.TeamEk) (teamBoxes *[]keybase1.TeamEkBoxMetadata, myTeamEKBoxed *keybase1.TeamEkBoxed, err error) {
defer g.CTraceTimed(ctx, "boxTeamEKForUsers", func() error { return err })()
myUID := g.Env.GetUID()
boxes := make([]keybase1.TeamEkBoxMetadata, 0, len(usersMetadata))
for uid, metadata := range usersMetadata {
recipientKey, err := libkb.ImportKeypairFromKID(metadata.Kid)
if err != nil {
return nil, nil, err
}
// Encrypting with a nil sender means we'll generate a random sender private key.
box, err := recipientKey.EncryptToString(teamEK.Seed[:], nil)
if err != nil {
return nil, nil, err
}
boxMetadata := keybase1.TeamEkBoxMetadata{
RecipientUID: uid,
RecipientGeneration: metadata.Generation,
Box: box,
}
boxes = append(boxes, boxMetadata)
if uid == myUID {
myTeamEKBoxed = &keybase1.TeamEkBoxed{
Box: box,
UserEkGeneration: metadata.Generation,
Metadata: teamEK.Metadata,
}
}
}
return &boxes, myTeamEKBoxed, err
}
type teamEKStatementResponse struct {
Sig *string `json:"sig"`
}
// Returns nil if the team has never published a teamEK. If the team has
// published a teamEK, but has since rolled their PTK without publishing a new
// one, this function will also return nil and log a warning. This is a
// transitional thing, and eventually when all "reasonably up to date" clients
// in the wild have EK support, we will make that case an error.
func fetchTeamEKStatement(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID) (statement *keybase1.TeamEkStatement, latestGeneration keybase1.EkGeneration, wrongKID bool, err error) {
defer g.CTraceTimed(ctx, "fetchTeamEKStatement", func() error { return err })()
apiArg := libkb.APIArg{
Endpoint: "team/team_ek",
SessionType: libkb.APISessionTypeREQUIRED,
NetContext: ctx,
Args: libkb.HTTPArgs{
"team_id": libkb.S{Val: string(teamID)},
},
}
res, err := g.GetAPI().Get(apiArg)
if err != nil {
return nil, latestGeneration, false, err
}
parsedResponse := teamEKStatementResponse{}
err = res.Body.UnmarshalAgain(&parsedResponse)
if err != nil {
return nil, latestGeneration, false, err
}
// If the result field in the response is null, the server is saying that
// the team has never published a teamEKStatement, stale or otherwise.
if parsedResponse.Sig == nil {
g.Log.CDebugf(ctx, "team has no teamEKStatement at all")
return nil, latestGeneration, false, nil
}
statement, latestGeneration, wrongKID, err = verifySigWithLatestPTK(ctx, g, teamID, *parsedResponse.Sig)
// Check the wrongKID condition before checking the error, since an error
// is still returned in this case. TODO: Turn this warning into an error
// after EK support is sufficiently widespread.
if wrongKID {
g.Log.CDebugf(ctx, "It looks like someone rolled the PTK without generating new ephemeral keys. They might be on an old version.")
return nil, latestGeneration, true, nil
} else if err != nil {
return nil, latestGeneration, false, err
}
return statement, latestGeneration, false, nil
}
func extractTeamEKStatementFromSig(sig string) (signerKey libkb.GenericKey, statement *keybase1.TeamEkStatement, err error) {
signerKey, payload, _, err := libkb.NaclVerifyAndExtract(sig)
if err != nil {
return signerKey, nil, err
}
parsedStatement := keybase1.TeamEkStatement{}
if err = json.Unmarshal(payload, &parsedStatement); err != nil {
return signerKey, nil, err
}
return signerKey, &parsedStatement, nil
}
// Verify that the blob is validly signed, and that the signing key is the
// given team's latest PTK, then parse its contents. If the blob is signed by
// the wrong KID, that's still an error, but we'll also return this special
// `wrongKID` flag. As a transitional measure while we wait for all clients in
// the wild to have EK support, callers will treat that case as "there is no
// key" and convert the error to a warning.
func verifySigWithLatestPTK(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID, sig string) (statement *keybase1.TeamEkStatement, latestGeneration keybase1.EkGeneration, wrongKID bool, err error) {
defer g.CTraceTimed(ctx, "verifySigWithLatestPTK", func() error { return err })()
// Parse the statement before we verify the signing key. Even if the
// signing key is bad (likely because of a legacy PTK roll that didn't
// include a teamEK statement), we'll still return the generation number.
signerKey, parsedStatement, err := extractTeamEKStatementFromSig(sig)
if err != nil {
return nil, latestGeneration, false, err
}
latestGeneration = parsedStatement.CurrentTeamEkMetadata.Generation
// Verify the signing key corresponds to the latest PTK. We load the team's
// from cache, but if the KID doesn't match, we try a forced reload to see
// if the cache might've been stale. Only if the KID still doesn't match
// after the reload do we complain.
team, err := teams.Load(ctx, g, keybase1.LoadTeamArg{
ID: teamID,
})
if err != nil {
return nil, latestGeneration, false, err
}
teamSigningKey, err := team.SigningKey()
if err != nil {
return nil, latestGeneration, false, err
}
if !teamSigningKey.GetKID().Equal(signerKey.GetKID()) {
// The latest PTK might be stale. Force a reload, then check this over again.
team, err := teams.Load(ctx, g, keybase1.LoadTeamArg{
ID: teamID,
ForceRepoll: true,
})
if err != nil {
return nil, latestGeneration, false, err
}
teamSigningKey, err = team.SigningKey()
if err != nil {
return nil, latestGeneration, false, err
}
if !teamSigningKey.GetKID().Equal(signerKey.GetKID()) {
return nil, latestGeneration, true, fmt.Errorf("teamEK returned for PTK signing KID %s, but latest is %s",
signerKey.GetKID(), teamSigningKey.GetKID())
}
}
// If we didn't short circuit above, then the signing key is correct.
// Return the parsed statement.
return parsedStatement, latestGeneration, false, nil
}
func filterStaleTeamEKStatement(ctx context.Context, g *libkb.GlobalContext, statement *keybase1.TeamEkStatement, merkleRoot libkb.MerkleRoot) (active []keybase1.TeamEkMetadata, err error) {
defer g.CTraceTimed(ctx, "filterStaleTeamEKStatement", func() error { return err })()
if statement == nil {
return nil, err
}
allMetadata := append([]keybase1.TeamEkMetadata{}, statement.ExistingTeamEkMetadata...)
allMetadata = append(allMetadata, statement.CurrentTeamEkMetadata)
for _, metadata := range allMetadata {
if !ctimeIsStale(metadata.Ctime, merkleRoot) {
active = append(active, metadata)
}
}
return active, nil
}
type teamMemberEKStatementResponse struct {
Sigs map[keybase1.UID]string `json:"sigs"`
}
// Returns nil if all team members have never published a teamEK. Verifies that
// the map of users the server returns are indeed valid team members of the
// team and all signatures verify correctly for the users.
func fetchTeamMemberStatements(ctx context.Context, g *libkb.GlobalContext, teamID keybase1.TeamID) (statementMap map[keybase1.UID]*keybase1.UserEkStatement, err error) {
defer g.CTraceTimed(ctx, "fetchTeamMemberStatements", func() error { return err })()
apiArg := libkb.APIArg{
Endpoint: "team/member_eks",
SessionType: libkb.APISessionTypeREQUIRED,
NetContext: ctx,
Args: libkb.HTTPArgs{
"team_id": libkb.S{Val: string(teamID)},
},
}
res, err := g.GetAPI().Get(apiArg)
if err != nil {
return nil, err
}
parsedResponse := teamMemberEKStatementResponse{}
err = res.Body.UnmarshalAgain(&parsedResponse)
if err != nil {
return nil, err
}
team, err := teams.Load(ctx, g, keybase1.LoadTeamArg{
ID: teamID,
ForceRepoll: true,
})
if err != nil {
return nil, err
}
statementMap = make(map[keybase1.UID]*keybase1.UserEkStatement)
for uid, sig := range parsedResponse.Sigs {
// Verify the server only returns actual members of our team.
upak, _, err := g.GetUPAKLoader().LoadV2(libkb.NewLoadUserByUIDArg(ctx, g, uid))
if err != nil {
return nil, err
}
uv := upak.Current.ToUserVersion()
isMember := team.IsMember(ctx, uv)
if !isMember {
return nil, fmt.Errorf("Server lied about team membership! %v is not a member of team %v", uv, teamID)
}
memberStatement, _, wrongKID, err := verifySigWithLatestPUK(ctx, g, uid, sig)
// Check the wrongKID condition before checking the error, since an error
// is still returned in this case. TODO: Turn this warning into an error
// after EK support is sufficiently widespread.
if wrongKID {
g.Log.CDebugf(ctx, "Member %v revoked a device without generating new ephemeral keys. They might be running an old version?", uid)
// Don't box for this member since they have no valid userEK
continue
} else if err != nil {
return nil, err
}
statementMap[uid] = memberStatement
}
return statementMap, nil
}