crypto/x509: bypass signature verification in CreateCertificate when using MD5WithRSA

Bypasses the signature verification check we previously added if the
signature algorithm is MD5WithRSA, as we only support this algorithm
for signing and not verification.

Change-Id: Idba6dbba8b365d6199d467526746b88a5f734af1
Reviewed-on: https://go-review.googlesource.com/c/go/+/264019
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Trust: Roland Shoemaker <roland@golang.org>

diff --git a/src/crypto/x509/x509.go b/src/crypto/x509/x509.go
index bcef54ddb4fe7f769ad5433161a5d507830a7b5b..b421d759732182d16903599acab13bd836705c3f 100644 (file)
--- a/src/crypto/x509/x509.go
+++ b/src/crypto/x509/x509.go
@@ -2156,8 +2156,12 @@ func CreateCertificate(rand io.Reader, template, parent *Certificate, pub, priv
        }
 
        // Check the signature to ensure the crypto.Signer behaved correctly.
-       if err := checkSignature(getSignatureAlgorithmFromAI(signatureAlgorithm), c.Raw, signature, key.Public()); err != nil {
-               return nil, fmt.Errorf("x509: signature over certificate returned by signer is invalid: %w", err)
+       // We skip this check if the signature algorithm is MD5WithRSA as we
+       // only support this algorithm for signing, and not verification.
+       if sigAlg := getSignatureAlgorithmFromAI(signatureAlgorithm); sigAlg != MD5WithRSA {
+               if err := checkSignature(sigAlg, c.Raw, signature, key.Public()); err != nil {
+                       return nil, fmt.Errorf("x509: signature over certificate returned by signer is invalid: %w", err)
+               }
        }
 
        return signedCert, nil

diff --git a/src/crypto/x509/x509_test.go b/src/crypto/x509/x509_test.go
index 5a39e61b3c2898bb2d5bdd7eed224d4d3bbbae08..47d78cf02afa5561dd740edcc6a1ab3b4e3294cc 100644 (file)
--- a/src/crypto/x509/x509_test.go
+++ b/src/crypto/x509/x509_test.go
@@ -2896,3 +2896,19 @@ func TestCreateCertificateBrokenSigner(t *testing.T) {
                t.Fatalf("CreateCertificate returned an unexpected error: got %q, want %q", err, expectedErr)
        }
 }
+
+func TestCreateCertificateMD5(t *testing.T) {
+       template := &Certificate{
+               SerialNumber:       big.NewInt(10),
+               DNSNames:           []string{"example.com"},
+               SignatureAlgorithm: MD5WithRSA,
+       }
+       k, err := rsa.GenerateKey(rand.Reader, 1024)
+       if err != nil {
+               t.Fatalf("failed to generate test key: %s", err)
+       }
+       _, err = CreateCertificate(rand.Reader, template, template, k.Public(), &brokenSigner{k.Public()})
+       if err != nil {
+               t.Fatalf("CreateCertificate failed when SignatureAlgorithm = MD5WithRSA: %s", err)
+       }
+}