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implement the plus variants of scram, to bind the authentication exchange to the tls connection

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to get the security benefits (detecting mitm attempts), explicitly configure
clients to use a scram plus variant, e.g. scram-sha-256-plus. unfortunately,
not many clients support it yet.

imapserver scram plus support seems to work with the latest imtest (imap test
client) from cyrus-sasl. no success yet with mutt (with gsasl) though.
This commit is contained in:
Mechiel Lukkien
2023-12-23 23:07:21 +01:00
parent 4701857d7f
commit e7478ed6ac
23 changed files with 690 additions and 189 deletions
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71
smtpclient/client_test.go
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@ -69,7 +69,7 @@ func TestClient(t *testing.T) {
Certificates: []tls.Certificate{cert},
}
test := func(msg string, opts options, auths []sasl.Client, expClientErr, expDeliverErr, expServerErr error) {
test := func(msg string, opts options, auth func(l []string, cs *tls.ConnectionState) (sasl.Client, error), expClientErr, expDeliverErr, expServerErr error) {
t.Helper()
if opts.tlsMode == "" {
@ -193,17 +193,32 @@ func TestClient(t *testing.T) {
writeline("334 " + base64.StdEncoding.EncodeToString([]byte("<123.1234@host>")))
readline("") // Proof
writeline("235 2.7.0 auth ok")
case "SCRAM-SHA-1", "SCRAM-SHA-256":
case "SCRAM-SHA-256-PLUS", "SCRAM-SHA-256", "SCRAM-SHA-1-PLUS", "SCRAM-SHA-1":
// Cannot fake/hardcode scram interactions.
var h func() hash.Hash
salt := scram.MakeRandom()
var iterations int
if t[0] == "SCRAM-SHA-1" {
switch t[0] {
case "SCRAM-SHA-1-PLUS", "SCRAM-SHA-1":
h = sha1.New
iterations = 2 * 4096
} else {
case "SCRAM-SHA-256-PLUS", "SCRAM-SHA-256":
h = sha256.New
iterations = 4096
default:
panic("missing case for scram")
}
var cs *tls.ConnectionState
if strings.HasSuffix(t[0], "-PLUS") {
if !haveTLS {
writeline("501 scram plus without tls not possible")
readline("QUIT")
writeline("221 ok")
result <- nil
return
}
xcs := serverConn.(*tls.Conn).ConnectionState()
cs = &xcs
}
saltedPassword := scram.SaltPassword(h, "test", salt, iterations)
@ -211,7 +226,7 @@ func TestClient(t *testing.T) {
if err != nil {
fail("bad base64: %w", err)
}
s, err := scram.NewServer(h, clientFirst)
s, err := scram.NewServer(h, clientFirst, cs, cs != nil)
if err != nil {
fail("scram new server: %w", err)
}
@ -283,7 +298,7 @@ func TestClient(t *testing.T) {
result <- err
panic("stop")
}
c, err := New(ctx, log.Logger, clientConn, opts.tlsMode, opts.tlsPKIX, localhost, opts.tlsHostname, Opts{Auth: auths, RootCAs: opts.roots})
client, err := New(ctx, log.Logger, clientConn, opts.tlsMode, opts.tlsPKIX, localhost, opts.tlsHostname, Opts{Auth: auth, RootCAs: opts.roots})
if (err == nil) != (expClientErr == nil) || err != nil && !errors.As(err, reflect.New(reflect.ValueOf(expClientErr).Type()).Interface()) && !errors.Is(err, expClientErr) {
fail("new client: got err %v, expected %#v", err, expClientErr)
}
@ -291,21 +306,21 @@ func TestClient(t *testing.T) {
result <- nil
return
}
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
err = client.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
if (err == nil) != (expDeliverErr == nil) || err != nil && !errors.Is(err, expDeliverErr) {
fail("first deliver: got err %v, expected %v", err, expDeliverErr)
}
if err == nil {
err = c.Reset()
err = client.Reset()
if err != nil {
fail("reset: %v", err)
}
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
err = client.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
if (err == nil) != (expDeliverErr == nil) || err != nil && !errors.Is(err, expDeliverErr) {
fail("second deliver: got err %v, expected %v", err, expDeliverErr)
}
}
err = c.Close()
err = client.Close()
if err != nil {
fail("close client: %v", err)
}
@ -357,11 +372,39 @@ test
test(msg, options{ehlo: true, smtputf8: false, needsmtputf8: true, nodeliver: true}, nil, nil, ErrSMTPUTF8Unsupported, nil)
test(msg, options{ehlo: true, starttls: true, tlsMode: TLSRequiredStartTLS, tlsPKIX: true, tlsHostname: dns.Domain{ASCII: "mismatch.example"}, nodeliver: true}, nil, ErrTLS, nil, &net.OpError{}) // Server TLS handshake is a net.OpError with "remote error" as text.
test(msg, options{ehlo: true, maxSize: len(msg) - 1, nodeliver: true}, nil, nil, ErrSize, nil)
test(msg, options{ehlo: true, auths: []string{"PLAIN"}}, []sasl.Client{sasl.NewClientPlain("test", "test")}, nil, nil, nil)
test(msg, options{ehlo: true, auths: []string{"CRAM-MD5"}}, []sasl.Client{sasl.NewClientCRAMMD5("test", "test")}, nil, nil, nil)
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-1"}}, []sasl.Client{sasl.NewClientSCRAMSHA1("test", "test")}, nil, nil, nil)
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-256"}}, []sasl.Client{sasl.NewClientSCRAMSHA256("test", "test")}, nil, nil, nil)
authPlain := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientPlain("test", "test"), nil
}
test(msg, options{ehlo: true, auths: []string{"PLAIN"}}, authPlain, nil, nil, nil)
authCRAMMD5 := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientCRAMMD5("test", "test"), nil
}
test(msg, options{ehlo: true, auths: []string{"CRAM-MD5"}}, authCRAMMD5, nil, nil, nil)
// todo: add tests for failing authentication, also at various stages in SCRAM
authSCRAMSHA1 := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientSCRAMSHA1("test", "test", false), nil
}
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-1"}}, authSCRAMSHA1, nil, nil, nil)
authSCRAMSHA1PLUS := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientSCRAMSHA1PLUS("test", "test", *cs), nil
}
test(msg, options{ehlo: true, starttls: true, auths: []string{"SCRAM-SHA-1-PLUS"}}, authSCRAMSHA1PLUS, nil, nil, nil)
authSCRAMSHA256 := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientSCRAMSHA256("test", "test", false), nil
}
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-256"}}, authSCRAMSHA256, nil, nil, nil)
authSCRAMSHA256PLUS := func(l []string, cs *tls.ConnectionState) (sasl.Client, error) {
return sasl.NewClientSCRAMSHA256PLUS("test", "test", *cs), nil
}
test(msg, options{ehlo: true, starttls: true, auths: []string{"SCRAM-SHA-256-PLUS"}}, authSCRAMSHA256PLUS, nil, nil, nil)
test(msg, options{ehlo: true, requiretls: false, needsrequiretls: true, nodeliver: true}, nil, nil, ErrRequireTLSUnsupported, nil)
// Set an expired certificate. For non-strict TLS, we should still accept it.