AWS API - Won't accept my Signature

I've tried everything here, but the Amazon Load Balancer API just will not accept my signature.

Whatever I try, I get a "403 SignatureDoesNotMatch" response. I'm pr开发者_运维技巧obably missing something obvious, but having spent hours trying to figure out what that is, I'm at the end of my tether. Please help!! Thanks.

Here's my code:

Public Sub DeregisterInstanceFromLoadBalance(ByVal strServerID As String)
    Dim strURL As String
    strURL = "http://elasticloadbalancing.amazonaws.com/?"
    Dim strTimestamp As String = PercentEncodeRfc3986(DateTime.UtcNow.ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"))

    Dim strParams As String
    strParams = "AWSAccessKeyId=<MY_API_KEY>" & _
    "&Action=DeregisterInstancesFromLoadBalancer" & _
    "&Instances.member.N=" & strServerID & _
    "&LoadBalancerName=ATTB" & _
    "&SignatureMethod=HmacSHA256" & _
    "&SignatureVersion=2" & _
    "&Timestamp=" & strTimestamp & _
    "&Version=2009-05-15"

    Dim strStringToSign As String = "GET\nelasticloadbalancing.amazonaws.com\n/\n" & strParams

    strURL = strURL & strParams & "&Signature=" & PercentEncodeRfc3986(HashString(strStringToSign))

    Dim wc As New WebClient()
    Dim strResponse As String
    strResponse = wc.DownloadString(strURL)

End Sub


Private Const PRIVATE_KEY As String = "<MY_PRIVATE_KEY>"

Private Function HashString(ByVal StringToHash As String) As String
    Dim Key() As Byte = Encoding.UTF8.GetBytes(PRIVATE_KEY)
    Dim XML() As Byte = Encoding.UTF8.GetBytes(StringToHash)
    Dim myHMACSHA256 As New System.Security.Cryptography.HMACSHA256(Key)
    Dim HashCode As Byte() = myHMACSHA256.ComputeHash(XML)
    Return Convert.ToBase64String(HashCode)
End Function


Private Function PercentEncodeRfc3986(ByVal str As String) As String

    str = HttpUtility.UrlEncode(str, System.Text.Encoding.UTF8)
    str = str.Replace("'", "%27").Replace("(", "%28").Replace(")", "%29").Replace("*", "%2A").Replace("!", "%21").Replace("%7e", "~").Replace("+", "%20").Replace("%7E", "~")

    Dim sbuilder As StringBuilder = New StringBuilder(str)
    For i As Int32 = 0 To sbuilder.Length - 1

        If sbuilder(i) = "%" Then
            If (Char.IsLetter(sbuilder(i + 1)) OrElse Char.IsLetter(sbuilder(i + 2))) Then
                sbuilder(i + 1) = Char.ToUpper(sbuilder(i + 1))
                sbuilder(i + 2) = Char.ToUpper(sbuilder(i + 2))
            End If
        End If
    Next
    Return sbuilder.ToString()
End Function

Ok, I got to the bottom of this. There were a few problems; not least Amazon's documentation.

• In VB.Net, I should have been using ControlChars.Lf rather than "\n"
• The Instances.member.N parameter as documented is just wrong, it should be
  Instances.member.[N].InstanceId, where [N] is the instance index,
  starting at 1. This was returning the rather confusing error message
  "LoadBalancerNotFound".
• The correct domain is elasticloadbalancing.[availability_zone].amazonaws.com; the examples used in the docs don't make this particularly clear either. (although domain usage is documented elsewhere)