[Spice-devel] [spice-protocol PATCH] Add SpiceLinkReply::ticket_encryption

[Christophe Fergeau]

Currently, SPICE tickets sent to the server are encrypted using a 1024 bit
public RSA key provided by the server. This key type/size is unfortunately
set in stone in the SPICE protocol as part of the SpiceLinkReply message,
and the key is sent by the server early in the link process (before the
server and the client agree on a SpiceLinkAuthMechanism).

This can be an issue if the server can't create a 1024 bit RSA key (for
example, if it was disabled because it's deemed not secure enough by the
server administrator). This happens for example in fips mode (
http://csrc.nist.gov/publications/fips/fips140-2/fips1402.pdf )

Luckily, the server gets the client caps before sending it this RSA
key, and it sends its caps in message containing this RSA key. By
advertising a new capability on the client and the server, it's thus
possible to indicate that other ways of encrypting the SPICE ticket are
supported by both client and server, and use that when available. When the
capability is present, an additional 'ticket_encryption' field is added to
the SpiceLinkReply structure to indicate that the SPICE ticket is not
encrypted using the legacy RSA 1024 bit key.

As the situation described above would happen in hardened setups, I've
added support for an unencrypted SPICE ticket which is only used for TLS
channels. For non-TLS channels, the old method is still used in order to
not send the ticket in plain text on unencrypted connections.
---
 spice/protocol.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/spice/protocol.h b/spice/protocol.h
index 961a303..f35c72e 100644
--- a/spice/protocol.h
+++ b/spice/protocol.h
@@ -56,8 +56,15 @@ enum {
     SPICE_COMMON_CAP_AUTH_SPICE,
     SPICE_COMMON_CAP_AUTH_SASL,
     SPICE_COMMON_CAP_MINI_HEADER,
+    SPICE_COMMON_CAP_PROTOCOL_PLAIN_TEXT_TICKET,
 };
 
+typedef enum {
+    SPICE_TICKET_ENCRYPTION_INVALID,
+    SPICE_TICKET_ENCRYPTION_RSA,
+    SPICE_TICKET_ENCRYPTION_NONE,
+} SpiceTicketEncryption;
+
 typedef struct SPICE_ATTR_PACKED SpiceLinkMess {
     uint32_t connection_id;
     uint8_t channel_type;
@@ -73,6 +80,7 @@ typedef struct SPICE_ATTR_PACKED SpiceLinkReply {
     uint32_t num_common_caps;
     uint32_t num_channel_caps;
     uint32_t caps_offset;
+    uint8_t ticket_encryption;
 } SpiceLinkReply;
 
 typedef struct SPICE_ATTR_PACKED SpiceLinkEncryptedTicket {
-- 
1.8.5.3