Cannot upload file to S3 using javascript

Question

I'm trying to upload a file to S3 based on this article: https://aws.amazon.com/articles/1434

However, I get the following error: "The request signature we calculated does not match the signature you provided. Check your key and signing method."

Obviously I do not calculate the signature correctly, but I cannot understand where's the error.

I'm using C# backend for signature calculations:

Here's my backend code:

 string policyStr = @"{""expiration"":""2014-05-01T12:00:00.000Z"",""conditions"":   [{""bucket"":""my-bucket""},[""starts-with"",""$key"",""uploads/${filename}""],{""acl"":""private""},{""success_action_redirect"":""http://localhost/""},[""starts-with"",""$Content-Type"",""text/plain""],[""content-length-range"",0,1048576]]}";

        string secretKey = "secret";
        string bucketName = "my-bucket";
        string filePath = string.Format(@"courseFiles\{0}", model.Name);

        var hash = new HMACSHA1(Encoding.UTF8.GetBytes(secretKey));
        var data = hash.ComputeHash(Encoding.UTF8.GetBytes(policyStr));

        var signature = Convert.ToBase64String(data);

        return new UploadFileResponseViewModel
        {
            AWSAccessKey = "accessKey",
            BucketName = bucketName,
            FilePath = filePath,
            Policy = Convert.ToBase64String(Encoding.UTF8.GetBytes(policyStr)),
            Signature = signature,
            Action = "https://my-bucket.s3.amazonaws.com/"
        };

The client side looks almost the same as the one explained in the article I mentioned. Does anyone knows what I'm doing wrong?

Dennis · Accepted Answer · 2014-04-11 09:08:51Z

Finally I found the solution.

Here's the correct way to calculate the signature just in case anyone needs it.

        string policyStr = @"{""expiration"":""2014-05-01T12:00:00.000Zr"",""conditions"":[{""bucket"":""my-bucket""},[""starts-with"",""$key"",""uploads""],{""acl"":""private""},{""success_action_redirect"":""http://localhost""},[""starts-with"",""$Content-Type"",""text/plain""],[""content-length-range"",0,1048576]]}";

        string secretKey = "secret";
        string bucketName = "my-bucket";
        string filePath = string.Format(@"courseFiles\{0}", model.Name);

        var hash = new HMACSHA1(Encoding.UTF8.GetBytes(secretKey));

        var policy = Convert.ToBase64String(Encoding.UTF8.GetBytes(policyStr));

        var data = hash.ComputeHash(Encoding.UTF8.GetBytes(policy));

        var signature = Convert.ToBase64String(data);

        return new UploadFileResponseViewModel
        {
            AWSAccessKey = "access",
            BucketName = bucketName,
            FilePath = filePath,
            Policy = policy,
            Signature = signature,
            Action = "https://my-bucket.s3.amazonaws.com/"
        };

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