Re: [!!Mass Mail]Re: "Wireshark-dev: Re: using pinfo structure to save data after first iteration"

[Neil Piercy <Neil.Piercy () ipaccess com>]

That was the intent: packet-rtp.[ch] already had the following added ready for this approach a long time back:

struct srtp_info
{
    guint      encryption_algorithm;              /* at present only NULL vs non-NULL matter */
    guint      auth_algorithm;                                           /* at present only NULL vs non-NULL matter */
    guint      mki_len;                                                                          /* number of octets 
used for the MKI in the RTP payload */
    guint      auth_tag_len;                                               /* number of octets used for the Auth Tag in 
the RTP payload */
#if 0       /* these are only needed once the dissector include the crypto functions to decrypt and/or authenticate */
    struct srtp_key_info **master_keys; /* an array of pointers to master keys and their info, the array and each key 
struct being wmem_file_scope'ed  */
    void       *enc_alg_info,                                              /* algorithm-dependent info struct - may be 
void for default alg with default params */
    void       *auth_alg_info                                             /* algorithm-dependent info struct - void for 
default alg with default params */
#endif
};

/* Add an SRTP conversation with the given details */
WS_DLL_PUBLIC
void srtp_add_address(packet_info *pinfo,
                     address *addr, int port,
                     int other_port,
                     const gchar *setup_method,
                     guint32 setup_frame_number,
                                                                                gboolean is_video,
                     rtp_dyn_payload_t *rtp_dyn_payload,
                     struct srtp_info *srtp_info);

There are small differences in packet-rtp handling when SRTP is used, but those differences are easy to handle inline.

Regards,
Neil

From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Anders Broman
Sent: 30 June 2015 11:41
To: Developer support list for Wireshark
Subject: [!!Mass Mail]Re: [Wireshark-dev] "Wireshark-dev: Re: using pinfo structure to save data after first iteration"

Hi,
Isn’t a SRTP packet in essence an RTP packet with encrypted payload? So I don’t see why it should be a problem to 
process the packet in packet-rtp.c
On the first pass.

Tip p_get_proto_data() can be used for per packet data. Are you using the development version as there seems to be some 
basic stuff for SRTP already in the dissector.
Regards
Anders

From: wireshark-dev-bounces () wireshark org<mailto:wireshark-dev-bounces () wireshark org> 
[mailto:wireshark-dev-bounces () wireshark org] On Behalf Of koundinya poluri
Sent: den 30 juni 2015 11:28
To: wireshark-dev
Subject: [Wireshark-dev] "Wireshark-dev: Re: using pinfo structure to save data after first iteration"

Hi, Anders,

I had a similar idea on how it should be done.I wanted to save some srtp related data once you processs the packets 
first time like creating a context which carries the ssrc and keys so that it can relate the packets to keys using the 
ssrc.But unfortunately wireshark cant differentiate between a rtp packet and srtp packet so it just processes the srtp 
packet as an rtp packet and changes the visited flag to one.

So cant use that flag which is generally used to differentiate the first iteration from the next ones.So i tried to put 
my own flag in the pinfo structure and modify it,but that did not work, as it looks like pinfo structure is a READ ONLY 
structure from a dissector's point of view.So how do I differentiate between iterations??

Is my understanding correct ?If so what is the solution to my problem?Thanks!

Also I am using UAT for entering keys!

-koundinya

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