x/crypto: Add pkcs12 package for reading pkcs12 data

Package pkcs12 provides some Go implementations of PKCS#12.
This implementation is distilled from https://tools.ietf.org/html/rfc7292 and
referenced documents. It is intented for decoding P12/PFX-stored certificate+key
for use with the crypto/tls package.

Package includes @dgryski's RC2 implementation as a sub package as requested in
https://github.com/golang/go/issues/10621.

Change-Id: I78401241e39cd0099e9082a3a227cf0a3a36e6d1
Reviewed-on: https://go-review.googlesource.com/11986
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>

pkcs12/bmp-string_test.go

@@ -0,0 +1,63 @@
+// Copyright 2015 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.
+
+package pkcs12
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+)
+
+var bmpStringTests = []struct {
+	in          string
+	expectedHex string
+	shouldFail  bool
+}{
+	{"", "0000", false},
+	// Example from https://tools.ietf.org/html/rfc7292#appendix-B.
+	{"Beavis", "0042006500610076006900730000", false},
+	// Some characters from the "Letterlike Symbols Unicode block".
+	{"\u2115 - Double-struck N", "21150020002d00200044006f00750062006c0065002d00730074007200750063006b0020004e0000", false},
+	// any character outside the BMP should trigger an error.
+	{"\U0001f000 East wind (Mahjong)", "", true},
+}
+
+func TestBMPString(t *testing.T) {
+	for i, test := range bmpStringTests {
+		expected, err := hex.DecodeString(test.expectedHex)
+		if err != nil {
+			t.Fatalf("#%d: failed to decode expectation", i)
+		}
+
+		out, err := bmpString(test.in)
+		if err == nil && test.shouldFail {
+			t.Errorf("#%d: expected to fail, but produced %x", i, out)
+			continue
+		}
+
+		if err != nil && !test.shouldFail {
+			t.Errorf("#%d: failed unexpectedly: %s", i, err)
+			continue
+		}
+
+		if !test.shouldFail {
+			if !bytes.Equal(out, expected) {
+				t.Errorf("#%d: expected %s, got %x", i, test.expectedHex, out)
+				continue
+			}
+
+			roundTrip, err := decodeBMPString(out)
+			if err != nil {
+				t.Errorf("#%d: decoding output gave an error: %s", i, err)
+				continue
+			}
+
+			if roundTrip != test.in {
+				t.Errorf("#%d: decoding output resulted in %q, but it should have been %q", i, roundTrip, test.in)
+				continue
+			}
+		}
+	}
+}