nfs/internal/krb5/aprep_test.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package krb5

import (
	"bytes"
	"testing"
)

// The AP-REP the acceptor answers with completes the client half of the
// context: it verifies under the session key, and nothing else does.
func TestClientAcceptRepRoundTrip(t *testing.T) {
	key := make([]byte, 32)
	for i := range key {
		key[i] = byte(i + 1)
	}
	client, token, err := ClientInit(EtypeAES256, key, "EXAMPLE.ORG", "nfs", "client")
	if err != nil {
		t.Fatal(err)
	}
	acceptor, aprep, err := AcceptInit(token, key)
	if err != nil {
		t.Fatal(err)
	}
	_ = acceptor
	if err := client.ClientAcceptRep(aprep); err != nil {
		t.Fatalf("accept rep: %v", err)
	}
	// The shared key makes both halves sign tokens the other verifies.
	mic, err := client.GetMIC([]byte("data"))
	if err != nil {
		t.Fatal(err)
	}
	if err := acceptor.VerifyMIC([]byte("data"), mic); err != nil {
		t.Fatalf("cross verify: %v", err)
	}

	// Anything but the genuine AP-REP is refused: a wrong tag, a wrong
	// message type, a body from another key.
	if err := client.ClientAcceptRep([]byte{0x6e, 0x00}); err == nil {
		t.Fatal("a two byte token accepted")
	}
	tampered := append([]byte{}, aprep...)
	tampered[len(tampered)-1] ^= 1
	if err := client.ClientAcceptRep(tampered); err == nil {
		t.Fatal("a tampered AP-REP accepted")
	}
	other, otoken, err := ClientInit(EtypeAES256, key, "EXAMPLE.ORG", "nfs", "other")
	if err != nil {
		t.Fatal(err)
	}
	if err := other.ClientAcceptRep(aprep); err == nil {
		t.Fatal("an AP-REP of another context accepted")
	}
	if bytes.Equal(otoken, token) {
		t.Fatal("two inits minted the same token")
	}
}