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virtualkey.go
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virtualkey.go
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// U2F token implementation for integration testing
package u2f
import (
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/sha256"
"crypto/x509"
"encoding/asn1"
"encoding/binary"
"encoding/json"
"fmt"
"math/big"
"time"
)
// Virtual U2F key
type VirtualKey struct {
attestationKey *ecdsa.PrivateKey
attestationCertBytes []byte
keys []keyInst
}
// Internal type for ASN1 coercion
type dsaSignature struct {
R, S *big.Int
}
// Key instance attached to an AppID (and keyHandle)
type keyInst struct {
Generated time.Time
AppID string
KeyHandle string
Private *ecdsa.PrivateKey
Counter int
}
// Create a virtual key
func NewVirtualKey() (*VirtualKey, error) {
// Generate attestation key
privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, err
}
vk := VirtualKey{}
vk.attestationKey = privateKey
vk.attestationCertBytes = generateCert(privateKey)
return &vk, nil
}
// Internal helper to generate certificates
func generateCert(privateKey *ecdsa.PrivateKey) []byte {
template := x509.Certificate{}
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
template.SerialNumber, _ = rand.Int(rand.Reader, serialNumberLimit)
template.KeyUsage = x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign
template.NotBefore = time.Now()
template.NotAfter = time.Now().Add(365 * 24 * time.Hour)
template.SignatureAlgorithm = x509.ECDSAWithSHA256
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &(privateKey.PublicKey), privateKey)
if err != nil {
fmt.Println(err)
}
return derBytes
}
// Internal helper to find key by application ID
func (vk *VirtualKey) getKeyByAppID(appId string) *keyInst {
for _, v := range vk.keys {
if v.AppID == appId {
return &v
}
}
return nil
}
// Internal helper to find key by application ID
func (vk *VirtualKey) getKeyByAppIDAndKeyHandle(appId string, keyHandle string) *keyInst {
for _, v := range vk.keys {
if (v.AppID == appId) && (v.KeyHandle == keyHandle) {
return &v
}
}
return nil
}
// Internal helper to generate a registration signature
func (vk *VirtualKey) generateRegistrationSig(appId string, clientData []byte, keyHandle string, publicKey *ecdsa.PublicKey, privateKey *ecdsa.PrivateKey) []byte {
appParam := sha256.Sum256([]byte(appId))
challenge := sha256.Sum256(clientData)
buf := []byte{0}
buf = append(buf, appParam[:]...)
buf = append(buf, challenge[:]...)
buf = append(buf, keyHandle...)
pk := elliptic.Marshal(publicKey.Curve, publicKey.X, publicKey.Y)
buf = append(buf, pk...)
digest := sha256.Sum256([]byte(buf))
r, s, err := ecdsa.Sign(rand.Reader, privateKey, digest[:])
if err != nil {
fmt.Println("Error generating signature")
fmt.Println(err)
}
dsaSig := dsaSignature{R: r, S: s}
asnSig, err := asn1.Marshal(dsaSig)
if err != nil {
fmt.Println("Error encoding signature")
fmt.Println(err)
}
return asnSig
}
// Handle a registration request
func (vk *VirtualKey) HandleRegisterRequest(req RegisterRequestMessage) (*RegisterResponse, error) {
// Check if a key is already registered
for _, k := range req.RegisteredKeys {
ki := vk.getKeyByAppIDAndKeyHandle(req.AppID, k.KeyHandle)
if ki != nil {
return nil, fmt.Errorf("Key already registered for AppID: %s (handle %s)", req.AppID, k.KeyHandle)
}
}
// Generate key components
privateKey, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
publicKey := privateKey.PublicKey
keyHandle := fmt.Sprintf("virtualkey-%d", len(vk.keys))
rr := RegisterResponse{}
// Generate client data
cd := ClientData{
Origin: req.AppID,
Challenge: req.RegisterRequests[0].Challenge,
}
cdJson, _ := json.Marshal(cd)
rr.ClientData = encodeBase64(cdJson)
// Generate registration data
var buf []byte
// Magic byte
buf = append(buf, 0x05)
// Public Key
buf = append(buf, elliptic.Marshal(elliptic.P256(), publicKey.X, publicKey.Y)...)
// Key handle
buf = append(buf, byte(len(keyHandle)))
buf = append(buf, []byte(keyHandle)...)
// X509 cert
buf = append(buf, vk.attestationCertBytes...)
// Signature
sig := vk.generateRegistrationSig(req.AppID, cdJson, keyHandle, &publicKey, vk.attestationKey)
buf = append(buf, sig...)
rr.RegistrationData = encodeBase64(buf)
// Create local key instance
keyInst := keyInst{
Generated: time.Now(),
AppID: req.AppID,
KeyHandle: keyHandle,
Private: privateKey,
Counter: 0,
}
vk.keys = append(vk.keys, keyInst)
return &rr, nil
}
// Internal helper to generate an authentication signature
func (vk *VirtualKey) generateAuthenticationSig(appId string, clientData []byte, signatureData []byte, privateKey *ecdsa.PrivateKey) []byte {
appParam := sha256.Sum256([]byte(appId))
challenge := sha256.Sum256(clientData)
var buf []byte
buf = append(buf, appParam[:]...)
buf = append(buf, signatureData...)
buf = append(buf, challenge[:]...)
digest := sha256.Sum256([]byte(buf))
r, s, err := ecdsa.Sign(rand.Reader, privateKey, digest[:])
if err != nil {
fmt.Println("Error generating signature")
fmt.Println(err)
}
dsaSig := dsaSignature{R: r, S: s}
asnSig, err := asn1.Marshal(dsaSig)
if err != nil {
fmt.Println("Error encoding signature")
fmt.Println(err)
}
return asnSig
}
// Handle an authentication request
func (vk *VirtualKey) HandleAuthenticationRequest(req SignRequestMessage) (*SignResponse, error) {
var keyInstance *keyInst = nil
// Find the registered key for this service
for _, k := range req.RegisteredKeys {
kh, _ := decodeBase64(k.KeyHandle)
ki := vk.getKeyByAppIDAndKeyHandle(req.AppID, string(kh))
if ki != nil {
keyInstance = ki
break
}
}
if keyInstance == nil {
return nil, fmt.Errorf("Key not found for AppID: %s", req.AppID)
}
sr := SignResponse{}
// Generate key handle
sr.KeyHandle = encodeBase64([]byte(keyInstance.KeyHandle))
// Increment key usage count
keyInstance.Counter = keyInstance.Counter + 1
// Build client data
cd := ClientData{
Origin: req.AppID,
Challenge: req.Challenge,
}
cdJson, _ := json.Marshal(cd)
sr.ClientData = encodeBase64(cdJson)
// Build signature data
var buf []byte
// User presence
buf = append(buf, 0x01)
// Use counter
countBuf := make([]byte, 4)
binary.BigEndian.PutUint32(countBuf, uint32(keyInstance.Counter))
buf = append(buf, countBuf...)
sig := vk.generateAuthenticationSig(req.AppID, cdJson, buf, keyInstance.Private)
buf = append(buf, sig...)
sr.SignatureData = encodeBase64(buf)
return &sr, nil
}