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Question:

Help with AWS signature version 4 using chilkat's crypt2 ActiveX component

Feb 15 '16 at 11:40

Hi

I've been trying to sign AWS requests using Chilkat's crypt2 ActiveX object

Amazon have a python example here:

http://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html

I'm trying to re-write this in VBscript using crypt2, however I can't get these Python functions working in VBScript:

def sign(key, msg):
    return hmac.new(key, msg.encode('utf-8'), hashlib.sha256).digest()

def getSignatureKey(key, dateStamp, regionName, serviceName):
    kDate = sign(('AWS4' + key).encode('utf-8'), dateStamp)
    kRegion = sign(kDate, regionName)
    kService = sign(kRegion, serviceName)
    kSigning = sign(kService, 'aws4_request')
    return kSigning

Here's my (not working) VBScript functions:

function sign_KeyBytes(bytekey, msg)
  crypt.HashAlgorithm = "sha256"
  crypt.Charset = "utf-8"
  crypt.SetHmacKeyBytes bytekey
  sign_KeyBytes = crypt.HashString(msg)
end function

function sign_KeyString(key, msg)
  crypt.HashAlgorithm = "sha256"
  crypt.Charset = "utf-8"
  crypt.SetHmacKeyString key
  sign_KeyString = crypt.HashString(msg)
end function

function getSignatureKey(key, dateStamp, regionName, serviceName)
  dim kDate : kDate = sign_KeyString("AWS4" + key, dateStamp)
  dim kRegion : kRegion = sign_KeyBytes(kDate, regionName)
  dim kService : kService = sign_KeyBytes(kRegion, serviceName)
  dim kSigning : kSigning = sign_KeyBytes(kService, "aws4_request")
  getSignatureKey = kSigning
end function

The VBScript only works if the required output is hex.

Can anybody help?

Cheers

Dave

---

Answer

Hi! If you're needing the Signature V4 for S3 requests via Chilkat HTTP, then it's already been implemented for the next Chilkat version release. Here's a pre-release download:

32-bit Download: http://www.chilkatsoft.com/download/preRelease/ChilkatAx-9.5.0-win32.zip
64-bit Download: http://www.chilkatsoft.com/download/preRelease/ChilkatAx-9.5.0-x64.zip

Computing the SignatureV4 is somewhat laborious and easy to get wrong. Here's my dilemma: I would like to help immediately, but I'm in the midst of designing potential new Chilkat classes relating to the subject matter, one of which may be a utility class to do the AWS SignatureV4 computation. If I spend time trying to do the SignatureV4 using Chilkat Crypt2, it delays the new development. If I rush and provide an AWS SignatureV4 object without careful thought and design, Chilkat would be stuck with a problematic API that plagues future development. So for now, I can't provide the immediate help, but I'm actually working on something that will be better in the long run.