forked from keybase/client
/
seitan.go
353 lines (301 loc) · 10.8 KB
/
seitan.go
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package teams
import (
"fmt"
"regexp"
"strings"
"crypto/hmac"
"crypto/rand"
"crypto/sha512"
"encoding/base64"
"encoding/hex"
"errors"
"golang.org/x/crypto/nacl/secretbox"
"golang.org/x/crypto/scrypt"
"golang.org/x/net/context"
libkb "github.com/keybase/client/go/libkb"
msgpack "github.com/keybase/client/go/msgpack"
keybase1 "github.com/keybase/client/go/protocol/keybase1"
)
// This is expected seitan token length, the secret "Invite Key" that
// is generated on one client and distributed to another via face-to-
// face meeting, use of a trusted courier etc.
//
// Seitan tokens have a '+' as the fifth character. We use this
// to distinguish from email invite tokens (and team names).
// See `IsSeitany`
const SeitanEncodedIKeyLength = 18
const seitanEncodedIKeyPlusOffset = 5
// Key-Base 30 encoding. lower case letters except "ilot", and digits except for '0' and '1'.
// See TestSeitanParams for a test to make sure these two parameters match up.
const KBase30EncodeStd = "abcdefghjkmnpqrsuvwxyz23456789"
const base30BitMask = byte(0x1f)
type SeitanVersion uint
const (
SeitanVersion1 SeitanVersion = 1
SeitanVersion2 SeitanVersion = 2
SeitanVersionInvitelink SeitanVersion = 3
)
// "Invite Key"
type SeitanIKey string
// "Seitan Packed Encrypted Key" All following 3 structs should be considered one.
// When any changes, version has to be bumped up.
type SeitanPKey struct {
_struct bool `codec:",toarray"` //nolint
Version SeitanVersion
TeamKeyGeneration keybase1.PerTeamKeyGeneration
RandomNonce keybase1.BoxNonce
EncryptedKeyAndLabel []byte // keybase1.SeitanKeyAndLabel MsgPacked and encrypted
}
func generateIKey(length int, plusOffset int) (str string, err error) {
alphabet := []byte(KBase30EncodeStd)
randEncodingByte := func() (byte, error) {
for {
var b [1]byte
_, err := rand.Read(b[:])
if err != nil {
return byte(0), err
}
i := int(b[0] & base30BitMask)
if i < len(alphabet) {
return alphabet[i], nil
}
}
}
var buf []byte
for i := 0; i < length; i++ {
if i == plusOffset {
buf = append(buf, '+')
} else {
b, err := randEncodingByte()
if err != nil {
return "", err
}
buf = append(buf, b)
}
}
return string(buf), nil
}
func GenerateIKey() (ikey SeitanIKey, err error) {
str, err := generateIKey(SeitanEncodedIKeyLength, seitanEncodedIKeyPlusOffset)
if err != nil {
return ikey, err
}
return SeitanIKey(str), err
}
var tokenPasteRegexp = regexp.MustCompile(`token\: [a-z0-9+]{16,28}`)
// Returns the string that might be the token, and whether the content looked like a token paste.
func ParseSeitanTokenFromPaste(token string) (parsed string, isSeitany bool) {
// If the person pasted the whole seitan SMS message in, then let's parse out the token
if strings.Contains(token, "token: ") {
m := tokenPasteRegexp.FindStringSubmatch(token)
if len(m) == 1 {
return strings.Split(m[0], " ")[1], true
}
return token, true
}
if groups := invitelinkIKeyRxx.FindStringSubmatch(token); groups != nil {
return groups[len(groups)-1], true
}
if IsSeitany(token) {
return token, true
}
return token, false
}
// ParseIKeyFromString safely creates SeitanIKey value from
// plaintext string. Only format is checked - any 18-character token
// with '+' character at position 5 can be "Invite Key". Alphabet is
// not checked, as it is only a hint for token generation and it can
// change over time, but we assume that token length stays the same.
func ParseIKeyFromString(token string) (ikey SeitanIKey, err error) {
if len(token) != SeitanEncodedIKeyLength {
return ikey, fmt.Errorf("invalid token length: expected %d characters, got %d", SeitanEncodedIKeyLength, len(token))
}
if token[seitanEncodedIKeyPlusOffset] != '+' {
return ikey, fmt.Errorf("invalid token format: expected %dth character to be '+'", seitanEncodedIKeyPlusOffset+1)
}
return SeitanIKey(strings.ToLower(token)), nil
}
func (ikey SeitanIKey) String() string {
return strings.ToLower(string(ikey))
}
const (
SeitanScryptCost = 1 << 10
SeitanScryptR = 8
SeitanScryptP = 1
SeitanScryptKeylen = 32
)
// "Stretched Invite Key"
type SeitanSIKey [SeitanScryptKeylen]byte
func generateSIKey(s string) (buf []byte, err error) {
buf, err = scrypt.Key([]byte(s), nil, SeitanScryptCost, SeitanScryptR, SeitanScryptP, SeitanScryptKeylen)
return buf, err
}
func (ikey SeitanIKey) GenerateSIKey() (sikey SeitanSIKey, err error) {
buf, err := generateSIKey(ikey.String())
if err != nil {
return sikey, err
}
copy(sikey[:], buf)
return sikey, nil
}
func generateTeamInviteIDRaw(secretKey []byte, payload []byte) ([]byte, error) {
mac := hmac.New(sha512.New, secretKey)
if _, err := mac.Write(payload); err != nil {
return nil, err
}
out := mac.Sum(nil)
out = out[0:15]
out = append(out, libkb.InviteIDTag)
return out, nil
}
func generateTeamInviteID(secretKey []byte, payload []byte) (id SCTeamInviteID, err error) {
out, err := generateTeamInviteIDRaw(secretKey, payload)
if err != nil {
return id, err
}
id = SCTeamInviteID(hex.EncodeToString(out))
return id, nil
}
func generateShortTeamInviteID(secretKey []byte, payload []byte) (id SCTeamInviteIDShort, err error) {
out, err := generateTeamInviteIDRaw(secretKey, payload)
if err != nil {
return id, err
}
id = SCTeamInviteIDShort(libkb.Base30.EncodeToString(out))
return id, nil
}
func (sikey SeitanSIKey) GenerateTeamInviteID() (id SCTeamInviteID, err error) {
type InviteStagePayload struct {
Stage string `codec:"stage" json:"stage"`
}
payload, err := msgpack.Encode(InviteStagePayload{Stage: "invite_id"})
if err != nil {
return id, err
}
return generateTeamInviteID(sikey[:], payload)
}
func packAndEncryptKeyWithSecretKey(secretKey keybase1.Bytes32, gen keybase1.PerTeamKeyGeneration, nonce keybase1.BoxNonce, packedKeyAndLabel []byte, version SeitanVersion) (pkey SeitanPKey, encoded string, err error) {
var encKey [libkb.NaclSecretBoxKeySize]byte = secretKey
var naclNonce [libkb.NaclDHNonceSize]byte = nonce
encryptedKeyAndLabel := secretbox.Seal(nil, packedKeyAndLabel, &naclNonce, &encKey)
pkey = SeitanPKey{
Version: version,
TeamKeyGeneration: gen,
RandomNonce: nonce,
EncryptedKeyAndLabel: encryptedKeyAndLabel,
}
packed, err := msgpack.Encode(pkey)
if err != nil {
return pkey, encoded, err
}
encoded = base64.StdEncoding.EncodeToString(packed)
return pkey, encoded, nil
}
func (ikey SeitanIKey) generatePackedEncryptedKeyWithSecretKey(secretKey keybase1.Bytes32, gen keybase1.PerTeamKeyGeneration, nonce keybase1.BoxNonce, label keybase1.SeitanKeyLabel) (pkey SeitanPKey, encoded string, err error) {
var keyAndLabel keybase1.SeitanKeyAndLabelVersion1
keyAndLabel.I = keybase1.SeitanIKey(ikey)
keyAndLabel.L = label
packedKeyAndLabel, err := msgpack.Encode(keybase1.NewSeitanKeyAndLabelWithV1(keyAndLabel))
if err != nil {
return pkey, encoded, err
}
return packAndEncryptKeyWithSecretKey(secretKey, gen, nonce, packedKeyAndLabel, SeitanVersion1)
}
func (ikey SeitanIKey) GeneratePackedEncryptedKey(ctx context.Context, team *Team, label keybase1.SeitanKeyLabel) (pkey SeitanPKey, encoded string, err error) {
appKey, err := team.SeitanInviteTokenKeyLatest(ctx)
if err != nil {
return pkey, encoded, err
}
var nonce keybase1.BoxNonce
if _, err = rand.Read(nonce[:]); err != nil {
return pkey, encoded, err
}
return ikey.generatePackedEncryptedKeyWithSecretKey(appKey.Key, appKey.KeyGeneration, nonce, label)
}
func SeitanDecodePKey(base64Buffer string) (pkey SeitanPKey, err error) {
packed, err := base64.StdEncoding.DecodeString(base64Buffer)
if err != nil {
return pkey, err
}
err = msgpack.Decode(&pkey, packed)
return pkey, err
}
func (pkey SeitanPKey) decryptKeyAndLabelWithSecretKey(secretKey keybase1.Bytes32) (ret keybase1.SeitanKeyAndLabel, err error) {
var encKey [libkb.NaclSecretBoxKeySize]byte = secretKey
var naclNonce [libkb.NaclDHNonceSize]byte = pkey.RandomNonce
plain, ok := secretbox.Open(nil, pkey.EncryptedKeyAndLabel, &naclNonce, &encKey)
if !ok {
return ret, errors.New("failed to decrypt seitan plain")
}
err = msgpack.Decode(&ret, plain)
if err != nil {
return ret, err
}
return ret, nil
}
func (pkey SeitanPKey) DecryptKeyAndLabel(ctx context.Context, team *Team) (ret keybase1.SeitanKeyAndLabel, err error) {
appKey, err := team.SeitanInviteTokenKeyAtGeneration(ctx, pkey.TeamKeyGeneration)
if err != nil {
return ret, err
}
return pkey.decryptKeyAndLabelWithSecretKey(appKey.Key)
}
// "Acceptance Key"
type SeitanAKey []byte
func generateAcceptanceKey(akeyPayload []byte, sikey []byte) (akey SeitanAKey, encoded string, err error) {
mac := hmac.New(sha512.New, sikey)
_, err = mac.Write(akeyPayload)
if err != nil {
return akey, encoded, err
}
out := mac.Sum(nil)
akey = out[:32]
encoded = base64.StdEncoding.EncodeToString(akey)
return akey, encoded, nil
}
func (sikey SeitanSIKey) GenerateAcceptanceKey(uid keybase1.UID, eldestSeqno keybase1.Seqno, unixTime int64) (akey SeitanAKey, encoded string, err error) {
type AKeyPayload struct {
Stage string `codec:"stage" json:"stage"`
UID keybase1.UID `codec:"uid" json:"uid"`
EldestSeqno keybase1.Seqno `codec:"eldest_seqno" json:"eldest_seqno"`
CTime int64 `codec:"ctime" json:"ctime"`
}
akeyPayload, err := msgpack.Encode(AKeyPayload{
Stage: "accept",
UID: uid,
EldestSeqno: eldestSeqno,
CTime: unixTime,
})
if err != nil {
return akey, encoded, err
}
return generateAcceptanceKey(akeyPayload, sikey[:])
}
// IsSeitany is a very conservative check of whether a given string looks like
// a Seitan token. We want to err on the side of considering strings Seitan
// tokens, since we don't mistakenly want to send botched Seitan tokens to the
// server.
func IsSeitany(s string) bool {
// use the minimum seitan offset value
return len(s) > seitanEncodedIKeyPlusOffset && strings.IndexByte(s, '+') > 1
}
// DeriveSeitanVersionFromToken returns possible seitan version based on the
// token. Different seitan versions have '+' characters at different position
// signifying version number. This function returning successfully does not mean
// that token is correct, valid, seitan. But returning an error means that token
// is definitely not a correct seitan token.
func DeriveSeitanVersionFromToken(token string) (version SeitanVersion, err error) {
switch {
case !IsSeitany(token):
return 0, errors.New("Invalid token, not seitan-y")
case len(token) > seitanEncodedIKeyPlusOffset && token[seitanEncodedIKeyPlusOffset] == '+':
return SeitanVersion1, nil
case len(token) > seitanEncodedIKeyV2PlusOffset && token[seitanEncodedIKeyV2PlusOffset] == '+':
return SeitanVersion2, nil
case len(token) > seitanEncodedIKeyInvitelinkPlusOffset &&
token[seitanEncodedIKeyInvitelinkPlusOffset] == '+':
return SeitanVersionInvitelink, nil
default:
return 0, errors.New("Invalid token, invalid '+' position")
}
}