test_sign_verify.go

func TestSignVerify(t *testing.T) {
	henk, _ := NewRsaIdentity()

	// A public message from Henk.
	// note that the message is a byte array, not just a string.
	msg := []byte("Wilders doet tenminste iets tegen de politiek.")
    
	// Henk signs the message with his private key. This will show the recipient
	// proof that this message is indeed from Henk
	sig, err := henk.Sign(msg)

	// now, if the message msg is public, anyone can read it.
	// the signature sig however, proves this message is from Henk.
	ingrid, _ := NewRsaIdentity()
	hans, _ := NewRsaIdentity()

	err = ingrid.Verify(msg, sig, henk.public)
	if err != nil {
		t.Errorf("Unable to verify Henk's signature; %s", err)
	}

	err = hans.Verify(msg, sig, henk.public)
	if err != nil {
		t.Errorf("Unable to verify Henk's signature; %s", err)
	}

    // Let's see if we can break the signature verification:
    
	// (1) changing the message
	err = hans.Verify([]byte("Wilders is een opruier"), sig, henk.public)
	if err == nil {
		t.Error("Expected an error as we changed the message")
	}

	// (2) changing the signature
	err = hans.Verify(msg, []byte("I am not the signature"), henk.public)
	if err == nil {
		t.Error("Expected an error as we changed the signature")
	}

	// (3) changing the public key
	err = hans.Verify(msg, sig, ingrid.public)
	if err == nil {
		t.Error("Expected an error as we changed the public key")
	}
}