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Nick
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| understanding the pic .hex file format |
 Posted: Thu Jul 07, 2005 9:30 pm |
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I'm adding a simple encryption to a boot loader.
":1000000010308A0000280000FF00030E8301A100C9"
is the first line of a hex file, can someone break down the line?
I figure it has the address, data, and a check sum value
also sometimes i see lines that start with :0 what are those?
":0A385000272C99008A01002800349B"
Thanks Nick |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Re: understanding the pic .hex file format |
| Posted: Fri Jul 08, 2005 4:08 am |
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| Nick wrote: | | I'm adding a simple encryption to a boot loader. |
If you are going to build simple encryption then one challenge you will have to work with is that the record format is "well known". Generally records are a fixed length - this gives an obvious clue to the record format. Certain records are constant such as type 4 records. When constant records occur it is relatively easy to break the encryption. You will effectively need to pad all records to the same length. You have to have a psuedo random pad otherwise type 4 records can be readily identified. Once these are identified then it becomes easier to determine the key to break the rest. The encryption algorithm has to be such that changing a single byte (such as would be the case of a minor code change) should result in the charge in a large number of records (ideally all records) without any obvious pattern.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
Last edited by asmallri on Fri Jul 08, 2005 8:30 am; edited 1 time in total |
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Nick
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| Posted: Fri Jul 08, 2005 5:06 am |
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1. Only encyrpt type 0 codes
2. Only encrypt the four digit hex- words and the checksum
those are going to be my rules.
example
non-enc
:1000000010308A0000280000FF00030E8301A100C9
enc
:10000000KFIJI4OI3KL409FKFKLEOI904983IO489390
so the format is not broken and can be programmed ;-)
Nick |
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