RE: how to generate keystream segment for SRTP header

I am implementing it for differant project. I have looked through the sourc=
e files and
found working of encryption  algo as

16 bits
 * <----->
 * +------+------+------+------+------+------+------+------+
 * |           nonce           |    pakcet index    |  ctr |---+
 * +------+------+------+------+------+------+------+------+   |
 *                                                             |
 * +------+------+------+------+------+------+------+------+   v
 * |                      salt                      |000000|->(+)
 * +------+------+------+------+------+------+------+------+   |
 *                                                             |
 *                                                        +---------+
 *                                                        | encrypt |
 *                                                        +---------+
 *                                                             |
 * +------+------+------+------+------+------+------+------+   |
 * |                    keystream block                    |<--+
 * +------+------+------+------+------+------+------+------+

Doesn't this daviates from SRTP RFC specification ?
And how should i choose nonce value?



Regards
Yogesh Patil


________________________________________
From: Werner Dittmann [[email protected]]
Sent: Tuesday, July 28, 2009 11:15 PM
To: Yogesh Devidas Patil
Cc: [email protected]
Subject: Re: [Ccrtp-devel] how to generate keystream segment for SRTP heade=
r

Do you implement SRTP for this RTP stack? We already have SRTP
avaliable since some years. If you like to implement SRTP for some
other project maybe you can have a look in the source files to
see how this is implemented.

Best Regards,
Werner

Yogesh Devidas Patil schrieb:
> Hi
> I am implementing SRTP and have  little confusion about it.
>
> as per my understanding of SRTP RFC3711,
> Initialization vector(IV) is generated as
>
> IV =3D (salt_key << 16) XOR (SSRC << 64) XOR (packet_index << 16)
>
> and  keystream segment (required for AES ICM ) is generated as
>
> Keystream_seg =3D E(k,IV) where k=3DSession key
> i.e Keystream_seg =3D k XOR IV
>
> is my understanding correct wrt SRTP standard??
>
> Wherein AES ICM RFC3686, keystream segment consists
> keystream_seg =3D NONCE || IV || Counter where Counter advances from init=
ial val=3D0.
>
> I mean how to relate these keystream_seg forming units in AES ICM(NONCE,I=
V,Counter) with SRTP header fields & fields computed from them??
>
> Second, how should i generate Master Key on sender side??And how to deriv=
e session keys from Master Key??
>
> Thanks in advance!!
>
>
> Regards
> Yogesh Patil
>
> A R I C E N T
>
> "DISCLAIMER: This message is proprietary to Aricent and is intended solel=
y for the use of the individual to whom it is addressed. It may contain pri=
vileged or confidential information and should not be circulated or used fo=
r any purpose other than for what it is intended. If you have received this=
 message in error,please notify the originator immediately. If you are not =
the intended recipient, you are notified that you are strictly prohibited f=
rom using, copying, altering, or disclosing the contents of this message. A=
ricent accepts no responsibility for loss or damage arising from the use of=
 the information transmitted by this email including damage from virus."
>
>
> _______________________________________________
> Ccrtp-devel mailing list
> [email protected]
> http://lists.gnu.org/mailman/listinfo/ccrtp-devel
>


"DISCLAIMER: This message is proprietary to Aricent and is intended solely =
for the use of the individual to whom it is addressed. It may contain privi=
leged or confidential information and should not be circulated or used for =
any purpose other than for what it is intended. If you have received this m=
essage in error,please notify the originator immediately. If you are not th=
e intended recipient, you are notified that you are strictly prohibited fro=
m using, copying, altering, or disclosing the contents of this message. Ari=
cent accepts no responsibility for loss or damage arising from the use of t=
he information transmitted by this email including damage from virus."