ssh: reject unsupported DSA key sizes
Fixes golang/go#19424.
Run-TryBot: Han-Wen Nienhuys
TryBot-Result: Gobot Gobot
@@ -367,6 +367,17 @@ func (r *dsaPublicKey) Type() string {
return "ssh-dss"
}
+func checkDSAParams(param *dsa.Parameters) error {
+ // SSH specifies FIPS 186-2, which only provided a single size
+ // (1024 bits) DSA key. FIPS 186-3 allows for larger key
+ // sizes, which would confuse SSH.
+ if l := param.P.BitLen(); l != 1024 {
+ return fmt.Errorf("ssh: unsupported DSA key size %d", l)
+ }
+
+ return nil
+}
+
// parseDSA parses an DSA key according to RFC 4253, section 6.6.
func parseDSA(in []byte) (out PublicKey, rest []byte, err error) {
var w struct {
@@ -377,12 +388,17 @@ func parseDSA(in []byte) (out PublicKey, rest []byte, err error) {
return nil, nil, err
}
- key := &dsaPublicKey{
- Parameters: dsa.Parameters{
+ param := dsa.Parameters{
P: w.P,
Q: w.Q,
G: w.G,
- },
+ }
+ if err := checkDSAParams(&param); err != nil {
+ return nil, nil, err
+ }
+
+ key := &dsaPublicKey{
+ Parameters: param,
Y: w.Y,
}
return key, w.Rest, nil
@@ -630,19 +646,28 @@ func (k *ecdsaPublicKey) CryptoPublicKey() crypto.PublicKey {
}
// NewSignerFromKey takes an *rsa.PrivateKey, *dsa.PrivateKey,
-// *ecdsa.PrivateKey or any other crypto.Signer and returns a corresponding
-// Signer instance. ECDSA keys must use P-256, P-384 or P-521.
+// *ecdsa.PrivateKey or any other crypto.Signer and returns a
+// corresponding Signer instance. ECDSA keys must use P-256, P-384 or
+// P-521. DSA keys must use parameter size L1024N160.
func NewSignerFromKey(key interface{}) (Signer, error) {
switch key := key.(type) {
case crypto.Signer:
return NewSignerFromSigner(key)
case *dsa.PrivateKey:
- return &dsaPrivateKey{key}, nil
+ return newDSAPrivateKey(key)
default:
return nil, fmt.Errorf("ssh: unsupported key type %T", key)
}
}
+func newDSAPrivateKey(key *dsa.PrivateKey) (Signer, error) {
+ if err := checkDSAParams(&key.PublicKey.Parameters); err != nil {
+ return nil, err
+ }
+
+ return &dsaPrivateKey{key}, nil
+}
+
type wrappedSigner struct {
signer crypto.Signer
pubKey PublicKey
