crypto/x509: test for negative RSA parameters.

Someone found software that generates negative numbers for the RSA
modulus in an X.509 certificate. Our error messages were very poor in
this case so this change improves that.

Update #4728
Return more helpful errors when RSA parameters are negative or zero.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7228072

diff --git a/src/pkg/crypto/x509/x509.go b/src/pkg/crypto/x509/x509.go
index 7983217696e57cb2b09ba2449fe022c531f93275..005d36da88043a735f6ae5b48807b31a7d6d63b6 100644 (file)
--- a/src/pkg/crypto/x509/x509.go
+++ b/src/pkg/crypto/x509/x509.go
@@ -660,6 +660,13 @@ func parsePublicKey(algo PublicKeyAlgorithm, keyData *publicKeyInfo) (interface{
                        return nil, err
                }
 
+               if p.N.Sign() <= 0 {
+                       return nil, errors.New("x509: RSA modulus is not a positive number")
+               }
+               if p.E <= 0 {
+                       return nil, errors.New("x509: RSA public exponent is not a positive number")
+               }
+
                pub := &rsa.PublicKey{
                        E: p.E,
                        N: p.N,