Suggest a fast way to do?
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So then why not focus on a much smaller problem? Trying to build the space shuttle in one setting will never work. You need to build it in pieces. When each of those smaller pieces are working, your overall problem will be solved.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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I have a CRC code for particuler string. I need to get the string corssspoding to CRC. My mean to say I need to generate all possible combination of string from lenght 1 to n untill I get the desired CRC value. I know, string may be different from original one. How can I acoomplish this in a fast way?
I have read through this chain (I was going to say 'string' but that would only confuse the issue) You have to understand folks here, many are just as curious about the 'why' as about the 'how'. You haven't answered 'why are you doing this?' To many, myself included, you have embarked on a totally useless exercise. Why in the world would you want a random string of characters that happens to generate the same CRC32 that you already have in your hand? You cannot possible reconstruct the original string so of what interest is a random string with the same CRC32. Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason. So, tell us 'why' you need such a string, you may find some folks who find the problem more interesting than it seems so far.
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I have read through this chain (I was going to say 'string' but that would only confuse the issue) You have to understand folks here, many are just as curious about the 'why' as about the 'how'. You haven't answered 'why are you doing this?' To many, myself included, you have embarked on a totally useless exercise. Why in the world would you want a random string of characters that happens to generate the same CRC32 that you already have in your hand? You cannot possible reconstruct the original string so of what interest is a random string with the same CRC32. Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason. So, tell us 'why' you need such a string, you may find some folks who find the problem more interesting than it seems so far.
Chuck O'Toole wrote:
Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason.
seems likely, to me.
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http://en.wikipedia.org/wiki/Lookup_table says: A Lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an 'expensive' computation or calculation operation. For example this is regularly done as part of CRC calculations.
#include <iostream.h>
// The CRC lookup table size is 8x32=256
const static unsigned int table[] =
{
0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419, 0x0706AF48F, 0x0E963A535, 0x09E6495A3,
0x00EDB8832, 0x079DCB8A4, 0x0E0D5E91E, 0x097D2D988, 0x009B64C2B, 0x07EB17CBD, 0x0E7B82D07, 0x090BF1D91,
0x01DB71064, 0x06AB020F2, 0x0F3B97148, 0x084BE41DE, 0x01ADAD47D, 0x06DDDE4EB, 0x0F4D4B551, 0x083D385C7,
0x0136C9856, 0x0646BA8C0, 0x0FD62F97A, 0x08A65C9EC, 0x014015C4F, 0x063066CD9, 0x0FA0F3D63, 0x08D080DF5,
0x03B6E20C8, 0x04C69105E, 0x0D56041E4, 0x0A2677172, 0x03C03E4D1, 0x04B04D447, 0x0D20D85FD, 0x0A50AB56B,
0x035B5A8FA, 0x042B2986C, 0x0DBBBC9D6, 0x0ACBCF940, 0x032D86CE3, 0x045DF5C75, 0x0DCD60DCF, 0x0ABD13D59,
0x026D930AC, 0x051DE003A, 0x0C8D75180, 0x0BFD06116, 0x021B4F4B5, 0x056B3C423, 0x0CFBA9599, 0x0B8BDA50F,
0x02802B89E, 0x05F058808, 0x0C60CD9B2, 0x0B10BE924, 0x02F6F7C87, 0x058684C11, 0x0C1611DAB, 0x0B6662D3D,
0x076DC4190, 0x001DB7106, 0x098D220BC, 0x0EFD5102A, 0x071B18589, 0x006B6B51F, 0x09FBFE4A5, 0x0E8B8D433,
0x07807C9A2, 0x00F00F934, 0x09609A88E, 0x0E10E9818, 0x07F6A0DBB, 0x0086D3D2D, 0x091646C97, 0x0E6635C01,
0x06B6B51F4, 0x01C6C6162, 0x0856530D8, 0x0F262004E, 0x06C0695ED, 0x01B01A57B, 0x08208F4C1, 0x0F50FC457,
0x065B0D9C6, 0x012B7E950, 0x08BBEB8EA, 0x0FCB9887C, 0x062DD1DDF, 0x015DA2D49, 0x08CD37CF3, 0x0FBD44C65,
0x04DB26158, 0x03AB551CE, 0x0A3BC0074, 0x0D4BB30E2, 0x04ADFA541, 0x03DD895D7, 0x0A4D1C46D, 0x0D3D6F4FB,
0x04369E96A, 0x0346ED9FC, 0x0AD678846, 0x0DA60B8D0, 0x044042D73, 0x033031DE5, 0x0AA0A4C5F, 0x0DD0D7CC9,
0x05005713C, 0x0270241AA, 0x0BE0B1010, 0x0C90C2086, 0x05768B525, 0x0206F85B3, 0x0B966D409, 0x0CE61E49F,
0x05EDEF90E, 0x029D9C998, 0x0B0D09822, 0x0C7D7A8B4, 0x059B33D17, 0x02EB40D81, 0x0B7BD5C3B, 0x0C0BA6CAD,
0x0EDB88320, 0x09ABFB3B6, 0x003B6E20C, 0x074B1D29A, 0x0EAD54739, 0x09DD277AF, 0x004DB2615, 0x073DC1683,
0x0E3630B12, 0x094643B84, 0x00D6D6A3E, 0x07A -
But I read somwhat like this somewhere that do some opeartion with calculated CRC untill we get zero? Is there something like this?
It sounds the same to me the same as trying to take a 128 bit md5 hash and regenerate the data that this hash corresponds to. You quite simply cannot do it accurately. a md5 may be used to hash anything from a 5 character password to a 700MB iso file - yet in both instances the hash will still be 128 bits long. While you can generate sequences of characters that will produce the same result when hashed/CRCed, there's no relaiable way without context of choosing the original string.
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I know I can not construct data from CRC, my aim is to get the string which generate the same CRC value
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I have a CRC code for particuler string. I need to get the string corssspoding to CRC. My mean to say I need to generate all possible combination of string from lenght 1 to n untill I get the desired CRC value. I know, string may be different from original one. How can I acoomplish this in a fast way?
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I know I can not construct data from CRC, my aim is to get the string which generate the same CRC value
john5632 wrote:
I know I can not construct data from CRC, my aim is to get the string which generate the same CRC value
You have just answered your own quesation them; trial and error is the only way to acchieve what you want, which is going to be very time consuming.
============================== Nothing to say.
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Having read all the above answers why do you persist in believing this is possible?
Unrequited desire is character building. OriginalGriff
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Having read all the above answers why do you persist in believing this is possible?
Unrequited desire is character building. OriginalGriff
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Richard MacCutchan wrote:
Having read all the above answers why do you persist in believing this is possible?
Head, meet brick wall. He just doesnt get it. :)
============================== Nothing to say.
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Richard MacCutchan wrote:
Having read all the above answers why do you persist in believing this is possible?
Head, meet brick wall. He just doesnt get it. :)
============================== Nothing to say.
:thumbsup: Thanks, I was a bit worried it was me!
Unrequited desire is character building. OriginalGriff
