Section 3.1 of RFC3711 states:
The "Encrypted Portion" of an SRTP packet consists of the encryption
of the RTP payload (including RTP padding when present) of the
equivalent RTP packet. The Encrypted Portion MAY be the exact size
of the plaintext or MAY be larger. Figure 1 shows the RTP payload
including any possible padding for RTP [RFC3550].
None of the pre-defined encryption transforms uses any padding; for
these, the RTP and SRTP payload sizes match exactly. New transforms
added to SRTP (following Section 6) may require padding, and may
hence produce larger payloads. RTP provides its own padding format
(as seen in Fig. 1), which due to the padding indicator in the RTP
header has merits in terms of compactness relative to paddings using
prefix-free codes. This RTP padding SHALL be the default method for
transforms requiring padding. Transforms MAY specify other padding
methods, and MUST then specify the amount, format, and processing of
their padding. It is important to note that encryption transforms
that use padding are vulnerable to subtle attacks, especially when
message authentication is not used [V02]. Each specification for a
new encryption transform needs to carefully consider and describe the
security implications of the padding that it uses. Message
authentication codes define their own padding, so this default does
not apply to authentication transforms.
Hope that helps.
On 2017-02-16 14:58, cisco.voip wrote:
All, can somebody tell me the typical srtp packet size and format vs
rtp packet size and format of a g711 encoded call.
I cannot find these number anywhere.
Thanks
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