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gitea/vendor/github.com/tstranex/u2f/auth.go

136 lines
3.4 KiB

// Go FIDO U2F Library
// Copyright 2015 The Go FIDO U2F Library Authors. All rights reserved.
// Use of this source code is governed by the MIT
// license that can be found in the LICENSE file.
package u2f
import (
"crypto/ecdsa"
"crypto/sha256"
"encoding/asn1"
"errors"
"math/big"
"time"
)
// SignRequest creates a request to initiate an authentication.
func (c *Challenge) SignRequest(regs []Registration) *WebSignRequest {
var sr WebSignRequest
sr.AppID = c.AppID
sr.Challenge = encodeBase64(c.Challenge)
for _, r := range regs {
rk := getRegisteredKey(c.AppID, r)
sr.RegisteredKeys = append(sr.RegisteredKeys, rk)
}
return &sr
}
// ErrCounterTooLow is raised when the counter value received from the device is
// lower than last stored counter value. This may indicate that the device has
// been cloned (or is malfunctioning). The application may choose to disable
// the particular device as precaution.
var ErrCounterTooLow = errors.New("u2f: counter too low")
// Authenticate validates a SignResponse authentication response.
// An error is returned if any part of the response fails to validate.
// The counter should be the counter associated with appropriate device
// (i.e. resp.KeyHandle).
// The latest counter value is returned, which the caller should store.
func (reg *Registration) Authenticate(resp SignResponse, c Challenge, counter uint32) (newCounter uint32, err error) {
if time.Now().Sub(c.Timestamp) > timeout {
return 0, errors.New("u2f: challenge has expired")
}
if resp.KeyHandle != encodeBase64(reg.KeyHandle) {
return 0, errors.New("u2f: wrong key handle")
}
sigData, err := decodeBase64(resp.SignatureData)
if err != nil {
return 0, err
}
clientData, err := decodeBase64(resp.ClientData)
if err != nil {
return 0, err
}
ar, err := parseSignResponse(sigData)
if err != nil {
return 0, err
}
if ar.Counter < counter {
return 0, ErrCounterTooLow
}
if err := verifyClientData(clientData, c); err != nil {
return 0, err
}
if err := verifyAuthSignature(*ar, &reg.PubKey, c.AppID, clientData); err != nil {
return 0, err
}
if !ar.UserPresenceVerified {
return 0, errors.New("u2f: user was not present")
}
return ar.Counter, nil
}
type ecdsaSig struct {
R, S *big.Int
}
type authResp struct {
UserPresenceVerified bool
Counter uint32
sig ecdsaSig
raw []byte
}
func parseSignResponse(sd []byte) (*authResp, error) {
if len(sd) < 5 {
return nil, errors.New("u2f: data is too short")
}
var ar authResp
userPresence := sd[0]
if userPresence|1 != 1 {
return nil, errors.New("u2f: invalid user presence byte")
}
ar.UserPresenceVerified = userPresence == 1
ar.Counter = uint32(sd[1])<<24 | uint32(sd[2])<<16 | uint32(sd[3])<<8 | uint32(sd[4])
ar.raw = sd[:5]
rest, err := asn1.Unmarshal(sd[5:], &ar.sig)
if err != nil {
return nil, err
}
if len(rest) != 0 {
return nil, errors.New("u2f: trailing data")
}
return &ar, nil
}
func verifyAuthSignature(ar authResp, pubKey *ecdsa.PublicKey, appID string, clientData []byte) error {
appParam := sha256.Sum256([]byte(appID))
challenge := sha256.Sum256(clientData)
var buf []byte
buf = append(buf, appParam[:]...)
buf = append(buf, ar.raw...)
buf = append(buf, challenge[:]...)
hash := sha256.Sum256(buf)
if !ecdsa.Verify(pubKey, hash[:], ar.sig.R, ar.sig.S) {
return errors.New("u2f: invalid signature")
}
return nil
}