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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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30
smtpclient/examples_test.go
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@ -2,10 +2,12 @@ package smtpclient_test
import (
"context"
"crypto/tls"
"log"
"net"
"strings"
"golang.org/x/exp/slices"
"golang.org/x/exp/slog"
"github.com/mjl-/mox/dns"
@ -29,11 +31,31 @@ func ExampleClient() {
ctx := context.Background()
tlsVerifyPKIX := true
opts := smtpclient.Opts{
Auth: []sasl.Client{
Auth: func(mechanisms []string, cs *tls.ConnectionState) (sasl.Client, error) {
// If the server is known to support a SCRAM PLUS variant, you should only use
// that, detecting and preventing authentication mechanism downgrade attacks
// through TLS channel binding.
username := "mjl"
password := "test1234"
// Prefer strongest authentication mechanism, allow up to older CRAM-MD5.
sasl.NewClientSCRAMSHA256("mjl", "test1234"),
sasl.NewClientSCRAMSHA1("mjl", "test1234"),
sasl.NewClientCRAMMD5("mjl", "test1234"),
if cs != nil && slices.Contains(mechanisms, "SCRAM-SHA-256-PLUS") {
return sasl.NewClientSCRAMSHA256PLUS(username, password, *cs), nil
}
if slices.Contains(mechanisms, "SCRAM-SHA-256") {
return sasl.NewClientSCRAMSHA256(username, password, true), nil
}
if cs != nil && slices.Contains(mechanisms, "SCRAM-SHA-1-PLUS") {
return sasl.NewClientSCRAMSHA1PLUS(username, password, *cs), nil
}
if slices.Contains(mechanisms, "SCRAM-SHA-1") {
return sasl.NewClientSCRAMSHA1(username, password, true), nil
}
if slices.Contains(mechanisms, "CRAM-MD5") {
return sasl.NewClientCRAMMD5(username, password), nil
}
// No mutually supported mechanism found, connection will fail.
return nil, nil
},
}
localname := dns.Domain{ASCII: "localhost"}