Question

I need to be able to create an RFC 2104-compliant HMAC with the SHA256 hash algorithm using vfp (foxpro)

Asked by: busycoder

http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/index.html?RequestAuthenticationArticle.html

I need a procedure that will successfully accomplish steps 7 and 8 from the page above (pasted here)

=======

The string to sign:

GET
webservices.amazon.com
/onca/xml
AWSAccessKeyId=00000000000000000000&ItemId=0679722769&Operation=I
temLookup&ResponseGroup=ItemAttributes%2COffers%2CImages%2CReview
s&Service=AWSECommerceService&Timestamp=2009-01-01T12%3A00%3A00Z&
Version=2009-01-06

Calculate an RFC 2104-compliant HMAC with the SHA256 hash algorithm using the string above with our "dummy" Secret Access Key: 1234567890. For more information about this step, see documentation and code samples for your programming language.

Nace+U3Az4OhN7tISqgs1vdLBHBEijWcBeCqL5xN9xg=   <-- This needs to be the result for the example with encryption key being 1234567890

=====

MSDN shows every example excluding foxpro (of course)
http://msdn.microsoft.com/en-us/library/system.security.cryptography.hmacsha256.aspx


Hopefully someone has experience with this, or can convert the vb code sucessfully from the page above.

Thanks all!!!!!

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Asked On
2009-08-18 at 13:08:49ID24662778
Tags

aws foxpro encryption HMAC SHA256

Topic

FoxPro Database

Participating Experts
1
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Comments
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Answers

 

by: Olaf_DoschkePosted on 2009-08-18 at 14:09:34ID: 25127708

HMAC itself is not very hard to code. See attached snippet. But foget that, it's even simpler: Per August, 10th, Craig Boyd has published the new version of his vfpencryption71.fll including HMAC support:

http://www.sweetpotatosoftware.com/SPSBlog/2009/08/09/MajorVFPEncryptionUpdate.aspx

With that it's something like SET LIBRARY TO vfpencryption71.fll, then Strconv(HMAC(lcRequest,'1234567890',2),13)

This doesn't turn out as you'd like, but I'm quite sure Craig's FLL is okay, as I use HMAC SHA-1 from it successfully. So I think you need to do something with the "string to sign", before computing the HMAC signature.

Bye, Olaf.

Set Library To Locfile('vfpencryption71.fll') Additive
 
Procedure HMACSHA(tcKey As String,tcMessage As String)
   #Define cnSha256 2
   Local lnIndex, lnKey, lcInner, lcOuter
 
   If (Len(tcKey) > 64)
      tcKey = Hash(tcKey,cnSha1)
   Endif
   tcKey = Padr(tcKey,64,Chr(0))
 
   lcInner = ''
   lcOuter = ''
   For lnIndex = 1 To 64
      lnKey   = Asc(Substr(tcKey,lnIndex,1))
      lcInner = lcInner + Chr(Bitxor(0x36,lnKey))
      lcOuter = lcOuter + Chr(Bitxor(0x5c,lnKey))
   Endfor
 
   Return Hash(lcOuter + Hash(lcInner + tcMessage, cnSha1), cnSha1)
Endproc

                                              
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by: busycoderPosted on 2009-08-18 at 15:25:45ID: 25128234

Thanks again Olaf!!!!! You are a life saver. I have one more favor to ask. The code below works and produces the desired example key. Is there a way that you know to do the "HASH" portion without using the fll library? Not a big deal, but this would make things more portable for me. You were right I had to work out what the example was considering a line feed before this would work correctly.

Thanks again! You are the best!

BC

Set Library To Locfile('vfpencryption71.fll') Additive
cr=CHR(10)
ts = 'GET'+cr
ts=ts+'webservices.amazon.com'+cr
ts=ts+'/onca/xml'+cr
ts=ts+'AWSAccessKeyId=00000000000000000000&ItemId=0679722769&Operation=ItemLookup&ResponseGroup=ItemAttributes%2COffers%2CImages%2CReviews&Service=AWSECommerceService&Timestamp=2009-01-01T12%3A00%3A00Z&Version=2009-01-06'
 
*!*	MESSAGEBOX(HMACSHA('1234567890',ts))
creturn = HMACSHA('1234567890',ts)
 
*!*	x=1
*!*	Do Whil x<=16
*!*		Messagebox(Strconv(cReturn, x),64,ALLTRIM(STR(x)))
*!*		x=x+1
*!*	ENDDO
 
Messagebox(Strconv(cReturn, 13),64,'Needs to be: Nace+U3Az4OhN7tISqgs1vdLBHBEijWcBeCqL5xN9xg=')
 
Procedure HMACSHA(tcKey As String,tcMessage As String)
   #Define cnSha256 2
   Local lnIndex, lnKey, lcInner, lcOuter
 
   If (Len(tcKey) > 64)
      tcKey = Hash(tcKey,cnSha256 )
   ENDIF
   
   tcKey = Padr(tcKey,64,Chr(0))
 
   lcInner = ''
   lcOuter = ''
   For lnIndex = 1 To 64
      lnKey   = Asc(Substr(tcKey,lnIndex,1))
      lcInner = lcInner + Chr(Bitxor(0x36,lnKey))
      lcOuter = lcOuter + Chr(Bitxor(0x5c,lnKey))
   Endfor
 
   Return Hash(lcOuter + Hash(lcInner + tcMessage, cnSha256 ), cnSha256 )
Endproc
                                              
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by: Olaf_DoschkePosted on 2009-08-19 at 00:02:15ID: 25130165

Thanks busycoder,

You oversaw, that I said, the new version of the FLL has a HMAC function built in, you don't need the HMACSHA procedure, simply call HMAC from the FLL.

I see you also want to get it done without the FLL at all. You find pseudocode in the wikipedia here: http://en.wikipedia.org/wiki/SHA_hash_functions#SHA-256_.28a_SHA-2_variant.29_pseudocode

But what dependencies do you fear? vfpencryption.fll only needs C++ runtimes, the same as VFP9 needs. So if your foxapp runs, the FLL also runs.

Bye, Olaf.

 

by: busycoderPosted on 2009-08-19 at 17:25:32ID: 31617299

This worked perfectly!!!

20120131-EE-VQP-002

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