[VOIPSEC] RTP or SRTP inside UDP - how understand?

[Hadriel Kaplan]

As I understand it (and I am by no means an encryption algorithm guy), what
you say is true except the modulo bytes are discarded by the encryptor.  The
ciphertext of AES in counter mode is always the same length as the
plaintext.
-hadriel


> -----Original Message-----
> From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] On
> Behalf Of Simon Horne
> Sent: Monday, March 27, 2006 5:21 PM
> To: Hadriel Kaplan; 'Simon Horne'; 'Sergey Vointsev'; voipsec at voipsa.org
> Subject: Re: [VOIPSEC] RTP or SRTP inside UDP - how understand?
> 
> AFAIK AES has a fixed block size of 128 bits or 16 bytes, A RTP payload
> may
> be any length (depending on the codec) but must be padded out to a
> multiple
> of 16kb for the cipher. So I have a payload of 28 bytes, this has to be
> padded out to 32 bytes (2x16) to put into the cipher which results in a 32
> byte encrypted block. There is a 4 byte variance.
> Reference
> http://en.wikipedia.org/wiki/Advanced_Encryption_Standard#Description_of_t
> he_cipher
> 
> Have I missed something?
> 
> Simon
> 
> 
> 
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