Files
crypto/openpgp/clearsign/clearsign_test.go
T
Filippo Valsorda c05e17bb3b openpgp/clearsign: reject potentially misleading headers and messages
Aida Mynzhasova of SEC Consult Vulnerability Lab reported that the
clearsign package accepts some malformed messages, which can make it
possible for an attacker to trick a human user (but not a Go program)
into thinking unverified text is part of the message.

For example, if in the following message the vertical tab character is
printed as a new line, a human observer could believe that the
unverified header text is part of the signed message.

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1\x0b\x0bThis text is part of the header.

Hello world!
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)

iJwEAQECAAYFAk8kMuEACgkQO9o98PRieSpMsAQAhmY/vwmNpflrPgmfWsYhk5O8
[...]
MyTpno24AjIAGb+mH1U=
=hIJ6
-----END PGP SIGNATURE-----

The OpenPGP specs are delightfully vague about purpose and validation of
these headers. RFC 4880, Section 7 says

    The cleartext signed message consists of:

        - The cleartext header '-----BEGIN PGP SIGNED MESSAGE-----' on a
        single line,

        - One or more "Hash" Armor Headers,

        - Exactly one empty line not included into the message digest,
        [...]

but also

    If MD5 is the only hash used, then an
    implementation MAY omit this header for improved V2.x compatibility.

and

    If more than one message digest is used in the signature, the "Hash"
    armor header contains a comma-delimited list of used message digests.

which seems to suggest that there can be zero or more Hash headers, each
with one or more algorithms, and no other header types.

Anyway, it's entirely unclear what security purpose, if any, the Hash
header accomplishes. If the hash is too weak to be secure or
unsupported, the verification will fail. Otherwise, the user shouldn't
care. Given its dubious function, avoid breaking abstractions to check
that it matches the signature, and just document it as unverified.

As for valid characters, RFC 4880 is silent, except reluctantly
mentioning that the Comment header can be UTF-8, but I am going to
assume that all hash algorithms will have ASCII names, because come on.

Even more importantly, reject non-Hash SIGNED MESSAGE headers (as opposed
to the SIGNATURE headers), to prevent a "Thank you!" message turning into

-----BEGIN PGP SIGNED MESSAGE-----
Reminder: I need you to wire $100k to 12345566 as soon as possible.

Thank you!
-----BEGIN PGP SIGNATURE-----
[...]

While at it, also check for trailing characters after the signed message
delimiter, as they are invalid and can be similarly used to confuse humans.

The Decode API is also unfortunate in that it doesn't return an error,
so we can't tell the user what's wrong with the message, but that's what
we've got.

Change-Id: I8a72c4851075337443d7a27e0b49a6b6e39f5a41
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/453011
Reviewed-by: Adam Langley <agl@google.com>
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/173778
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2019-04-24 20:35:55 +00:00

323 lines
9.1 KiB
Go

// Copyright 2012 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 clearsign
import (
"bytes"
"fmt"
"testing"
"golang.org/x/crypto/openpgp"
"golang.org/x/crypto/openpgp/packet"
)
func testParse(t *testing.T, input []byte, expected, expectedPlaintext string) {
b, rest := Decode(input)
if b == nil {
t.Fatal("failed to decode clearsign message")
}
if !bytes.Equal(rest, []byte("trailing")) {
t.Errorf("unexpected remaining bytes returned: %s", string(rest))
}
if b.ArmoredSignature.Type != "PGP SIGNATURE" {
t.Errorf("bad armor type, got:%s, want:PGP SIGNATURE", b.ArmoredSignature.Type)
}
if !bytes.Equal(b.Bytes, []byte(expected)) {
t.Errorf("bad body, got:%x want:%x", b.Bytes, expected)
}
if !bytes.Equal(b.Plaintext, []byte(expectedPlaintext)) {
t.Errorf("bad plaintext, got:%x want:%x", b.Plaintext, expectedPlaintext)
}
keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewBufferString(signingKey))
if err != nil {
t.Errorf("failed to parse public key: %s", err)
}
if _, err := openpgp.CheckDetachedSignature(keyring, bytes.NewBuffer(b.Bytes), b.ArmoredSignature.Body); err != nil {
t.Errorf("failed to check signature: %s", err)
}
}
func TestParse(t *testing.T) {
testParse(t, clearsignInput, "Hello world\r\nline 2", "Hello world\nline 2\n")
testParse(t, clearsignInput2, "\r\n\r\n(This message has a couple of blank lines at the start and end.)\r\n\r\n", "\n\n(This message has a couple of blank lines at the start and end.)\n\n\n")
}
func TestParseWithNoNewlineAtEnd(t *testing.T) {
input := clearsignInput
input = input[:len(input)-len("trailing")-1]
b, rest := Decode(input)
if b == nil {
t.Fatal("failed to decode clearsign message")
}
if len(rest) > 0 {
t.Errorf("unexpected remaining bytes returned: %s", string(rest))
}
}
var signingTests = []struct {
in, signed, plaintext string
}{
{"", "", ""},
{"a", "a", "a\n"},
{"a\n", "a", "a\n"},
{"-a\n", "-a", "-a\n"},
{"--a\nb", "--a\r\nb", "--a\nb\n"},
// leading whitespace
{" a\n", " a", " a\n"},
{" a\n", " a", " a\n"},
// trailing whitespace (should be stripped)
{"a \n", "a", "a\n"},
{"a ", "a", "a\n"},
// whitespace-only lines (should be stripped)
{" \n", "", "\n"},
{" ", "", "\n"},
{"a\n \n \nb\n", "a\r\n\r\n\r\nb", "a\n\n\nb\n"},
}
func TestSigning(t *testing.T) {
keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewBufferString(signingKey))
if err != nil {
t.Errorf("failed to parse public key: %s", err)
}
for i, test := range signingTests {
var buf bytes.Buffer
plaintext, err := Encode(&buf, keyring[0].PrivateKey, nil)
if err != nil {
t.Errorf("#%d: error from Encode: %s", i, err)
continue
}
if _, err := plaintext.Write([]byte(test.in)); err != nil {
t.Errorf("#%d: error from Write: %s", i, err)
continue
}
if err := plaintext.Close(); err != nil {
t.Fatalf("#%d: error from Close: %s", i, err)
continue
}
b, _ := Decode(buf.Bytes())
if b == nil {
t.Errorf("#%d: failed to decode clearsign message", i)
continue
}
if !bytes.Equal(b.Bytes, []byte(test.signed)) {
t.Errorf("#%d: bad result, got:%x, want:%x", i, b.Bytes, test.signed)
continue
}
if !bytes.Equal(b.Plaintext, []byte(test.plaintext)) {
t.Errorf("#%d: bad result, got:%x, want:%x", i, b.Plaintext, test.plaintext)
continue
}
if _, err := openpgp.CheckDetachedSignature(keyring, bytes.NewBuffer(b.Bytes), b.ArmoredSignature.Body); err != nil {
t.Errorf("#%d: failed to check signature: %s", i, err)
}
}
}
// We use this to make test keys, so that they aren't all the same.
type quickRand byte
func (qr *quickRand) Read(p []byte) (int, error) {
for i := range p {
p[i] = byte(*qr)
}
*qr++
return len(p), nil
}
func TestMultiSign(t *testing.T) {
if testing.Short() {
t.Skip("skipping long test in -short mode")
}
zero := quickRand(0)
config := packet.Config{Rand: &zero}
for nKeys := 0; nKeys < 4; nKeys++ {
nextTest:
for nExtra := 0; nExtra < 4; nExtra++ {
var signKeys []*packet.PrivateKey
var verifyKeys openpgp.EntityList
desc := fmt.Sprintf("%d keys; %d of which will be used to verify", nKeys+nExtra, nKeys)
for i := 0; i < nKeys+nExtra; i++ {
e, err := openpgp.NewEntity("name", "comment", "email", &config)
if err != nil {
t.Errorf("cannot create key: %v", err)
continue nextTest
}
if i < nKeys {
verifyKeys = append(verifyKeys, e)
}
signKeys = append(signKeys, e.PrivateKey)
}
input := []byte("this is random text\r\n4 17")
var output bytes.Buffer
w, err := EncodeMulti(&output, signKeys, nil)
if err != nil {
t.Errorf("EncodeMulti (%s) failed: %v", desc, err)
}
if _, err := w.Write(input); err != nil {
t.Errorf("Write(%q) to signer (%s) failed: %v", string(input), desc, err)
}
if err := w.Close(); err != nil {
t.Errorf("Close() of signer (%s) failed: %v", desc, err)
}
block, _ := Decode(output.Bytes())
if string(block.Bytes) != string(input) {
t.Errorf("Inline data didn't match original; got %q want %q", string(block.Bytes), string(input))
}
_, err = openpgp.CheckDetachedSignature(verifyKeys, bytes.NewReader(block.Bytes), block.ArmoredSignature.Body)
if nKeys == 0 {
if err == nil {
t.Errorf("verifying inline (%s) succeeded; want failure", desc)
}
} else {
if err != nil {
t.Errorf("verifying inline (%s) failed (%v); want success", desc, err)
}
}
}
}
}
const signatureBlock = `
-----BEGIN PGP SIGNATURE-----
Version: OpenPrivacy 0.99
yDgBO22WxBHv7O8X7O/jygAEzol56iUKiXmV+XmpCtmpqQUKiQrFqclFqUDBovzS
vBSFjNSiVHsuAA==
=njUN
-----END PGP SIGNATURE-----
`
var invalidInputs = []string{
`
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
(This message was truncated.)
`,
`
-----BEGIN PGP SIGNED MESSAGE-----garbage
Hash: SHA256
_o/
` + signatureBlock,
`
garbage-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
_o/
` + signatureBlock,
`
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA` + "\x0b\x0b" + `256
_o/
` + signatureBlock,
`
-----BEGIN PGP SIGNED MESSAGE-----
NotHash: SHA256
_o/
` + signatureBlock,
}
func TestParseInvalid(t *testing.T) {
for i, input := range invalidInputs {
if b, rest := Decode([]byte(input)); b != nil {
t.Errorf("#%d: decoded a bad clearsigned message without any error", i)
} else if string(rest) != input {
t.Errorf("#%d: did not return all data with a bad message", i)
}
}
}
var clearsignInput = []byte(`
;lasjlkfdsa
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Hello world
line 2
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)
iJwEAQECAAYFAk8kMuEACgkQO9o98PRieSpMsAQAhmY/vwmNpflrPgmfWsYhk5O8
pjnBUzZwqTDoDeINjZEoPDSpQAHGhjFjgaDx/Gj4fAl0dM4D0wuUEBb6QOrwflog
2A2k9kfSOMOtk0IH/H5VuFN1Mie9L/erYXjTQIptv9t9J7NoRBMU0QOOaFU0JaO9
MyTpno24AjIAGb+mH1U=
=hIJ6
-----END PGP SIGNATURE-----
trailing`)
var clearsignInput2 = []byte(`
asdlfkjasdlkfjsadf
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
(This message has a couple of blank lines at the start and end.)
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.11 (GNU/Linux)
iJwEAQEIAAYFAlPpSREACgkQO9o98PRieSpZTAP+M8QUoCt/7Rf3YbXPcdzIL32v
pt1I+cMNeopzfLy0u4ioEFi8s5VkwpL1AFmirvgViCwlf82inoRxzZRiW05JQ5LI
ESEzeCoy2LIdRCQ2hcrG8pIUPzUO4TqO5D/dMbdHwNH4h5nNmGJUAEG6FpURlPm+
qZg6BaTvOxepqOxnhVU=
=e+C6
-----END PGP SIGNATURE-----
trailing`)
var signingKey = `-----BEGIN PGP PRIVATE KEY BLOCK-----
Version: GnuPG v1.4.10 (GNU/Linux)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=zNCn
-----END PGP PRIVATE KEY BLOCK-----
`