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Saturday, May 17, 2008

PDU Format Extraction

Peace be upon you,

How are you guys? I hope that all of you is Ok, today I am going to show you peace of code that I really like, this code actually doing a very nice thing, which is extracting the characters from the SMS, what I mean here if you have any knowledge about SMS, you will now that it sent in 7 bits format called "PDU" Protocol Data Unit, the extraction of this data is not tough, but I just demonstrating the beauty of the bit wise operation and how it minimize the code size, here is the first peace of code, it suppose to extract the PDU data and make it readable ASCII characters data.

Function Name : PDUChunk
Author : Ahmed Essam
Date : 17 - 05 - 2008
Purpose : Convert 7 bytes of PDU data to 8 bytes of Char data

History Revision
17-05-2008 Created AEssam
char* PDUChunk(char* Source)
// it is just constant to the block size
int nBase = 8 ;
// Allocate 9 bytes because of the nature of null terminated sting
char *cpResult = new char[9];
// Clean the allocated memory

// in each loop we keep part of the byte for the next byte, this the variable
// which will hold the rest of the opreation to the next character
unsigned char cRest = 0;
// in Each loop the mask changes, because the shifting that happen from using 7 bits from 8 bits
char cMask = 128;
for(int nLoop=0;nLoop<=nBase;nLoop++)
// shifting the current set of bits to the appropriate location,
// and put the rest the we keep from last byte at the end of the current bits set
cpResult[nLoop] = ((Source[nLoop] & ~cMask)<< (nLoop%nBase)) (cRest>>(nBase-(nLoop%nBase)));
// keep the unused set of bits to the next opreation
cRest = Source[nLoop] & cMask;
// update the mask for the next usage
cMask = cMask >> 1;

Function Name : PDUChunk
Author : Ahmed Essam
Date : 17 - 05 - 2008
Purpose : Convert PDU data to of Char data
History Revision
17-05-2008 Created AEssam
char* FromPDU2Char(char* Source,int len)
// Loops counter to end the loop by the end of the data retrieval
int nLoops = 0;
// This to calculate the CHAR length, after extracting it from PDU
// This is faster to avoid using floating point, if we are using floating point it will be (len/7) * 8)
int nTotalLen = (((len*10)/7) * 8)/10;
// Allocate memory for the end char array
char *cpResult = new char[nTotalLen];
// Clean the memory up
// Extract the Char from the PDU
char *cpChunk = PDUChunk(Source + nLoops);
// Safe concatenation for the end result
// Delte the return char array
delete []cpChunk;
// Add the chunck size to the loop counter
// Examining the loops count against the length of the PDU data
while (nLoops<len);
// Return the result string

Here is the code that consume that code

char cpSourceMSG[] = "\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83\xc1\x60\x30\x18\x0c\x06\x83";

// Extract the characters from the pSourceMSG
char * cpExtractedMSG = FromPDU2Char(cpSourceMSG,sizeof(cpSourceMSG));

this message suppose to be a SMS full of "A", which means 160 character of A, the function up there is not 100% safe but it is working OK for now,

in the function "PDUChunk", you will notice there is line full of bit wise operations

that is the line I am talking about

cpResult[nLoop] = ((Source[nLoop] & ~cMask)<< (nLoop%nBase)) (cRest>>(nBase-(nLoop%nBase)));

this line should do all the targeted purpose, it suppose to get the latest shifting value and apply it on the current value of PDU, then do ORING with the remain value from the last operation, I know that you may not understand what I am talking about, here is link that explains that issue in details

anyways, the coming part is nice, the coming part is we are going to extract the Unicode SMS, actually it doesn't need any effort, it just little endian and we are going to make it big endian

char cpUnicodeMSG[] = "\x06\x33\x06\x2a\x06\x2a\x06\x35\x06\x44\x00\x20\x06\x28\x06\x43\x06\x45\x00\x20\x06\x45\x06\x48\x06\x28\x06\x4a\x06\x46\x06\x4a\x06\x44\x00\x20\x06\x44\x06\x25\x06\x33\x06\x2a\x06\x43\x06\x45\x06\x27\x06\x44\x00\x20\x06\x28\x06\x4a\x06\x27\x06\x46\x06\x27\x06\x2a\x06\x43\x06\x45\x00\x20\x06\x48\x06\x41\x06\x42\x06\x27\x06\x4b\x00\x20\x06\x44\x06\x2a\x06\x39\x06\x44\x06\x4a\x06\x45\x06\x27\x06\x2a\x00\x20\x06\x2c\x06\x47\x06\x27\x06\x32\x00\x20\x06\x27\x06\x44\x06\x25\x06\x2a\x06\x35\x06\x27\x06\x44\x06\x27\x06\x2a";
char *cpFlippedArray = new char[sizeof(cpUnicodeMSG)];
for(int n=0;n<sizeof(cpUnicodeMSG)/2;n++)
cpFlippedArray[n*2] = cpUnicodeMSG[(n*2)+1] ;
cpFlippedArray[(n*2)+1] = cpUnicodeMSG[n*2] ;
TCHAR *wsUnicodeString = (TCHAR*)cpFlippedArray ;

it suppose that you will have the result string the wsUnicodeString, after that you are free to do what ever you want to with this string.

Most of you will say, that you see the string in normal Wide Character if you are developing something for MAPI, like MAPI Rule, actually the idea here is little low level, I got this data from the RIL, Radio Interface Layer, I did small application that sniff GSM, and keep everything, this how I got this RAW data, here it is all about the memory and data format in the memory, it is really nice to play with the bit wise stuff :D, I hope that you like the post.

At the end I hope that this post was useful and helpful.

Thanks for your time.

Ahmed Essam

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Tuesday, May 13, 2008

MIT, Waiting for all of us

Peace be upon you
I hope that you are all OK, today I am going to recommend (as usual :D), let us begin with summary to save your time, MIT has opened there materials Video Audio and text for all people so you can watch the courses that is in the institute for free just visit there web site
So let us begin the cool part, it is something like conversation between me and someone :D.
Short cuts : Me -> M, Someone who I am talking to -> S

M: Do u know that MIT has open there course materials for free?
S: Wait a second what is MIT?
M: it is "Massachusetts Institute of Technology", it is in USA, Cambridge, Massachusetts, it has strong emphasis on scientific and technological
S: so what are you telling me?
M: simply this HUGE decent educational place has done a very nice thing which is, opening there courses materials for people for free, in many formats Audio, Video and Text.
S: it is good, but what does it mean any way?
M: for guy like me, I seek so hard to starting master in Egypt and I couldn't do that for many "Educational lows" problems with me, so I start looking for something to study and learn online, I found many places that provide online master degree but I though that it is useless, I remember when "Mohamed Hegazy- My colleague in Imaginet (MobiDiv)" told me once that MIT has open there materials for all people, so I start checking it out, and I found it more than amazing.
S: you know it seems cool, but I still don't feel that is "it is not that important".
M: look the issue here is our career always want more and more from us in the area of keeping up with technology, I think if we could follow what this courses provide we would have very good progress in our career.
S: I think, you are right but not all people will like to go on with that.
M: I agree with you, but sometimes we need to do some stuff in teams, that's what I am thinking about, imagine that we arrange some kind of group to provide "Free knowledge" that is based on MIT courses, it could be amazing to provide such thing in Arabian community, specially when the educational standards in Egypt are very low, the community will do DEEP impact, the students may join us, to get better understanding for things.
S: you know it is a great idea, but I am not going to join, I am already loaded.
M: look, you can just listen when we have sessions about what we have studied, what do u think?
S: OK, that's seem to be fine, I will start with listening then may be I become one of the team :)
M: I hope all the Egyptian community join us :)
S: OK, can I go for my work, :) I am sorry I am little tough about it.
M: of course, I have work too, it was a very nice time that I have spent with you :), Bye
S: me too pleased talking to you, bye, keep me up to date ;)

At the end, I hope that you got something useful to help you managing your life, thanks for your time :)

Ahmed Essam
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