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Encryption-packetization

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Post new topic   Reply to topic   Printer-friendly version    Networking/Security Forums Index -> Cryptographic Theory and Cryptanalysis - Internal and Transmission Security

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jul123
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PostPosted: Tue Jul 27, 2004 12:29 pm    Post subject: Encryption-packetization Reply with quote

hi


what we have:

there are many events and each event has image , text , audio ,video.

now...

we want to send this data on a wireless network...for this we have planned data packetization and encryption.

We have a doubt on the sequence...ie, first we should packetize it and then encrypt it or the other way.

we have packetization module which is basically used to check the data type and to relate which packet is from which event and the sequence no. of the packet.this will also have acknowledgement and retransmision schemes.

plz suggest what should be the first step..to packetize or to encrypt and why..
thanks
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data
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PostPosted: Tue Jul 27, 2004 3:19 pm    Post subject: Reply with quote

hi,

first you should compress it (the info)and then encrypt it.This helps increasing the difficulty for the attacker to find patterns in the cipher text,as well as reduce the number of blocks to be encrypted as well as sent over the network.

You can then open a stream socket and send the data as fixed blocks, fix the block size suitable for the wireless network.

This may break up between the 'block size' of the encrypted blocks. but you dont have to worry about it, since the network will automatically take care of segmentation and reassembly.

Data.
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jul123
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PostPosted: Wed Jul 28, 2004 5:35 am    Post subject: Encryption - Packetization Reply with quote

but how will i know that which packet belongs to which event. and what is the type of the data.... if we are not packetizing the data.

We have decided to first packetize the data and then encrypt...but now how to take the time factor into account,
for decryption it will take more time than encryption and then on the network also it will take some amount of time to transmit....so how can we finilize this issue that how much time gap we should allow before retransmitting in case of a failure or packet loss
i hope i am able to convey my doubt....but plz do ask more if required and reply
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PostPosted: Wed Jul 28, 2004 3:18 pm    Post subject: Reply with quote

Quote:
how can we finilize this issue that how much time gap we should allow before retransmitting in case of a failure or packet loss


There are many dynamic algorithms for dynamically calculating Round Trip Time(RTT). The most widely used mechansim to determine the time gap for TCP applications is the Karn's Algorithm
Look at the URl below

http://www.soi.wide.ad.jp/class/20020032/slides/11/36.html
http://cs.baylor.edu/~donahoo/NIUNet/tcptour/javis/tcp_karn.html

You keep doubling the time out,till the first time all the acknowledgements are received sucessfully and use that as the time out timer. You can aslo try asking this question in the Networking Section in here.


As for packet loss, the TCP will take care of retransmitting them correctly. You could use an API like BREW for coding this application.

A friend did a project, sending encrypted packets our a wireless network using BREW API, where in (512 bytes) was read from a file at a time and put into a buffer and sent over the network. This value 512 bytes was chosen as they didnot find any packet drops,starting from a buffer of 16 bytes and increasing.

Data.
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cpconstantine
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PostPosted: Wed Jul 28, 2004 8:12 pm    Post subject: Reply with quote

hrm, if I understand the question correctly, he's asking 'what's more efficient' - sending an encrypted datastream over an unencrypted channel, or sending an unencrypted datastream over an encrypted channel'

(ie is the application handlind the crypto, or is the network?)

need more data - are you wrinting your own protocol stack module here? just doing something in userspace?

details!
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