crypto/openpgp: add DSA signature support.

src/pkg/crypto/openpgp/packet/packet.go

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // This package implements parsing and serialisation of OpenPGP packets, as
 // specified in RFC 4880.
 package packet
 
 import (
+        "big"
         "crypto/aes"
         "crypto/cast5"
         "crypto/cipher"
         "crypto/openpgp/error"
         "io"
         "os"
 )
 
 // readFull is the same as io.ReadFull except that reading zero bytes returns
 // ErrUnexpectedEOF rather than EOF.
@@ skipping 358 matching lines @@
         if err != nil {
                 return
         }
         bitLength = uint16(buf[0])<<8 | uint16(buf[1])
         numBytes := (int(bitLength) + 7) / 8
         mpi = make([]byte, numBytes)
         _, err = readFull(r, mpi)
         return
 }
 
-// writeMPI serializes a big integer to r.
+// writeMPI serializes a big integer to w.
 func writeMPI(w io.Writer, bitLength uint16, mpiBytes []byte) (err os.Error) {
         _, err = w.Write([]byte{byte(bitLength >> 8), byte(bitLength)})
         if err == nil {
                 _, err = w.Write(mpiBytes)
         }
         return
 }
+
+// writeBig serializes a *big.Int to w.
+func writeBig(w io.Writer, i *big.Int) os.Error {
+        return writeMPI(w, uint16(i.BitLen()), i.Bytes())
+}