[Spice-devel] [PATCH 5/9] Add support for SpiceLinkReply::ticket_encryption

[Marc-André Lureau]

----- Original Message -----
> 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.
> 
> This commit is a first step towards that. It sends an additional field as
> part of SpiceLinkReply. The size of the SpiceLinkReply message is sent to
> the client, and the client accesses the caps by using the caps_offset
> field, so we can safely send this additional field to older clients as they
> will not look at it.
> ---
>  server/reds.c | 1 +
>  spice-common  | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/server/reds.c b/server/reds.c
> index f45092b..fbeb1a5 100644
> --- a/server/reds.c
> +++ b/server/reds.c
> @@ -1404,6 +1404,7 @@ static int reds_send_link_ack(RedLinkInfo *link)
>      ack.num_channel_caps = channel_caps->num_caps;
>      header.size += (ack.num_common_caps + ack.num_channel_caps) *
>      sizeof(uint32_t);
>      ack.caps_offset = sizeof(SpiceLinkReply);
> +    ack.ticket_encryption = SPICE_TICKET_ENCRYPTION_RSA;

Since there is a header.size, this shouldn't break older clients, ack.


>      if (!reds_generate_ticket_pubkey(link, &ack))
>          goto end;
>  
> diff --git a/spice-common b/spice-common
> index 57ce430..a26bc7b 160000
> --- a/spice-common
> +++ b/spice-common
> @@ -1 +1 @@
> -Subproject commit 57ce430ccd66bd1ca2447c14503234cfb88e2365
> +Subproject commit a26bc7befc3d4f15f4bd8ea05f01e63ee0308350
> --
> 1.8.5.3
> 
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