Bump github.com/google/certificate-transparency-go to v1.0.21

vendor/github.com/google/certificate-transparency-go/tls/types.go

@@ -14,7 +14,13 @@
 
 package tls
 
-import "fmt"
+import (
+	"crypto"
+	"crypto/dsa"
+	"crypto/ecdsa"
+	"crypto/rsa"
+	"fmt"
+)
 
 // DigitallySigned gives information about a signature, including the algorithm used
 // and the signature value.  Defined in RFC 5246 s4.7.
@@ -94,3 +100,18 @@ func (s SignatureAlgorithm) String() string {
 		return fmt.Sprintf("UNKNOWN(%d)", s)
 	}
 }
+
+// SignatureAlgorithmFromPubKey returns the algorithm used for this public key.
+// ECDSA, RSA, and DSA keys are supported. Other key types will return Anonymous.
+func SignatureAlgorithmFromPubKey(k crypto.PublicKey) SignatureAlgorithm {
+	switch k.(type) {
+	case *ecdsa.PublicKey:
+		return ECDSA
+	case *rsa.PublicKey:
+		return RSA
+	case *dsa.PublicKey:
+		return DSA
+	default:
+		return Anonymous
+	}
+}