[Ccrtp-devel] how to generate keystream segment for SRTP header

[Yogesh Devidas Patil]

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 = (salt_key << 16) XOR (SSRC << 64) XOR (packet_index << 16)

and  keystream segment (required for AES ICM ) is generated as

Keystream_seg = E(k,IV) where k=Session key
i.e Keystream_seg = k XOR IV

is my understanding correct wrt SRTP standard??

Wherein AES ICM RFC3686, keystream segment consists
keystream_seg = NONCE || IV || Counter where Counter advances from initial 
val=0.

I mean how to relate these keystream_seg forming units in AES 
ICM(NONCE,IV,Counter) with SRTP header fields & fields computed from them??

Second, how should i generate Master Key on sender side??And how to derive 
session keys from Master Key??

Thanks in advance!!


Regards
Yogesh Patil

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