Add private (rsa) key to string method

keygen.go

@@ -2,6 +2,8 @@ package dns
 
 import (
 	"os"
+        "strconv"
+        "big"
 	"crypto/rsa"
 	"crypto/rand"
 )
@@ -59,3 +61,47 @@ func (r *RR_DNSKEY) Generate(bits int) (PrivateKey, os.Error) {
 	}
 	return nil, nil // Dummy return
 }
+
+// Convert a PrivateKey to a string. This
+// string has the same format as the private-key-file
+// of BIND9 (Private-key-format: v1.3). It needs some
+// info from the key (hashing, keytag), so its a method
+// of the RR_DNSKEY.
+func (r *RR_DNSKEY) PrivateKeyToString(p PrivateKey) (s string) {
+        switch t := p.(type) {
+        case *rsa.PrivateKey:
+                algorithm := strconv.Itoa(int(r.Algorithm)) + " (" + alg_str[r.Algorithm] + ")"
+                modulus := unpackBase64(t.PublicKey.N.Bytes())
+                pub := make([]byte, 1)
+                pub[0] = uint8(t.PublicKey.E) // Todo does not fit with binds 65537 exp!
+                publicExponent := unpackBase64(pub)
+                privateExponent := unpackBase64(t.D.Bytes())
+                prime1 := unpackBase64(t.P.Bytes())
+                prime2 := unpackBase64(t.Q.Bytes())
+                // Calculate Exponent1/2 and Coefficient as per: http://en.wikipedia.org/wiki/RSA#Using_the_Chinese_remainder_algorithm
+                // and from: http://code.google.com/p/go/issues/detail?id=987
+                one := big.NewInt(1)
+                minusone := big.NewInt(-1)
+                p_1 := big.NewInt(0).Sub(t.P, one)
+                q_1 := big.NewInt(0).Sub(t.Q, one)
+                exp1 := big.NewInt(0).Mod(t.D, p_1)
+                exp2 := big.NewInt(0).Mod(t.D, q_1)
+                coeff := big.NewInt(0).Exp(t.Q, minusone, t.P)
+
+                exponent1 := unpackBase64(exp1.Bytes())
+                exponent2 := unpackBase64(exp2.Bytes())
+                coefficient := unpackBase64(coeff.Bytes())
+
+                s = "Private-key-format: v1.3\n" +
+                        "Algorithm: " + algorithm + "\n" +
+                        "Modules: " + modulus + "\n" +
+                        "PublicExponent: " + publicExponent + "\n" +
+                        "PrivateExponent: " + privateExponent + "\n" +
+                        "Prime1: " + prime1 + "\n" +
+                        "Prime2: " + prime2 + "\n" +
+                        "Exponent1: " + exponent1 + "\n" +
+                        "Exponent2: " + exponent2 + "\n" +
+                        "Coefficient: " + coefficient + "\n"
+        }
+        return
+}