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Question:

How to Encode an Azure Signature?

Aug 03 '12 at 14:59

I’m close to getting a working example of using Chilkat libs to talk to Azure (Http/Crypt2 C++) my issue is it appears I’m not calculating the signature correctly, any chance I could get you to take a look at this and tell me where I might be going wrong?

//simple testing function
void local_was_sign_request(const char *request,CkString &str, wchar_t *name, wchar_t *primekey)
{
      CkCrypt2 enc;
      CkString strauth,strfinal,strid,strkey;
      strid.setStringU(name);
      strkey.setStringU(primekey);

enc.UnlockComponent("30-day trial");
      enc.put_HashAlgorithm("sha256");
      enc.SetHmacKeyString(strkey.getAnsi());
      enc.put_Charset("utf8");
      enc.put_EncodingMode("base64");
      enc.HmacStringENC(request,strauth);
      str.append("SharedKey ");
      str.append(strid.getAnsi());
      str.append(":");
      str.append(strauth.getUtf8());
}

According to MSFT the mechanism for signing is as follows:

Encoding the Signature

To encode the signature, call the HMAC-SHA256 algorithm on the UTF-8-encoded signature string and encode the result as Base64. Use the following format (shown as pseudocode):

Signature=Base64(HMAC-SHA256(UTF8(StringToSign)))

Based on what I’m doing I would think I’m doing exactly that?

---

Answer

what Microsoft leaves out is that they key they provide on their website is base64 encoded, so you have to use SetHmacKeyEncoded(key,"base64")

//simple testing function
void local_was_sign_request(const char request,CkString &str, wchar_t name, wchar_t *primekey)
{
      CkCrypt2 enc;
      CkString strauth,strfinal,strid,strkey;
      strid.setStringU(name);
      strkey.setStringU(primekey);

enc.UnlockComponent("30-day trial");
      enc.put_HashAlgorithm("sha256");
      enc.SetHmacKeyEncoded(strkey.getAnsi(),"base64");
      enc.put_Charset("utf8");
      enc.put_EncodingMode("base64");
      enc.HmacStringENC(request,strauth);
      str.append("SharedKey ");
      str.append(strid.getAnsi());
      str.append(":");
      str.append(strauth.getUtf8());
}