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Amazon Redshift
Management Guide (API Version 2012-12-01)

Signing an HTTP Request

Amazon Redshift requires that every request you send to the management API be authenticated with a signature. This topic explains how to sign your requests.

If you are using one of the AWS Software Development Kits (SDKs) or the AWS Command Line Interface, request signing is handled automatically, and you can skip this section. For more information about using AWS SDKs, see Using the Amazon Redshift Management Interfaces. For more information about using the Amazon Redshift Command Line Interface, go to Amazon Redshift Command Line Reference.

To sign a request, you calculate a digital signature by using a cryptographic hash function. A cryptographic hash is a function that returns a unique hash value that is based on the input. The input to the hash function includes the text of your request and your secret access key. The hash function returns a hash value that you include in the request as your signature. The signature is part of the Authorization header of your request.

Note

For API access, you need an access key ID and secret access key. For more information about creating access keys, see How Do I Get Security Credentials? in the AWS General Reference.

After Amazon Redshift receives your request, it recalculates the signature by using the same hash function and input that you used to sign the request. If the resulting signature matches the signature in the request, Amazon Redshift processes the request; otherwise, the request is rejected.

Amazon Redshift supports authentication using AWS Signature Version 4. The process for calculating a signature is composed of three tasks. These tasks are illustrated in the example that follows.

  • Task 1: Create a Canonical Request

    Rearrange your HTTP request into a canonical form. Using a canonical form is necessary because Amazon Redshift uses the same canonical form to calculate the signature it compares with the one you sent.

  • Task 2: Create a String to Sign

    Create a string that you will use as one of the input values to your cryptographic hash function. The string, called the string to sign, is a concatenation of the name of the hash algorithm, the request date, a credential scope string, and the canonicalized request from the previous task. The credential scope string itself is a concatenation of date, region, and service information.

  • Task 3: Create a Signature

    Create a signature for your request by using a cryptographic hash function that accepts two input strings, your string to sign and a derived key. The derived key is calculated by starting with your secret access key and using the credential scope string to create a series of hash-based message authentication codes (HMAC-SHA256).

Example Signature Calculation

The following example walks you through the details of creating a signature for CreateCluster request. You can use this example as a reference to check your own signature calculation method. Other reference calculations are included in the Signature Version 4 Test Suite of the Amazon Web Services Glossary.

You can use a GET or POST request to send requests to Amazon Redshift. The difference between the two is that for the GET request your parameters are sent as query string parameters. For the POST request they are included in the body of the request. The example below shows a POST request.

The example assumes the following:

  • The time stamp of the request is Fri, 07 Dec 2012 00:00:00 GMT.

  • The endpoint is US East (Northern Virginia) Region, us-east-1.

The general request syntax is:
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https://redshift.us-east-1.amazonaws.com/ ?Action=CreateCluster &ClusterIdentifier=examplecluster &MasterUsername=masteruser &MasterUserPassword=12345678Aa &NumberOfNode=2 &NodeType=ds1.xlarge &Version=2012-12-01 &x-amz-algorithm=AWS4-HMAC-SHA256 &x-amz-credential=AKIAIOSFODNN7EXAMPLE/20121207/us-east-1/redshift/aws4_request &x-amz-date=20121207T000000Z &x-amz-signedheaders=content-type;host;x-amz-date

The canonical form of the request calculated for Task 1: Create a Canonical Request is:

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POST / content-type:application/x-www-form-urlencoded; charset=utf-8 host:redshift.us-east-1.amazonaws.com x-amz-date:20121207T000000Z content-type;host;x-amz-date 55141b5d2aff6042ccd9d2af808fdf95ac78255e25b823d2dbd720226de1625d

The last line of the canonical request is the hash of the request body. The third line in the canonical request is empty because there are no query parameters for this API.

The string to sign for Task 2: Create a String to Sign is:

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AWS4-HMAC-SHA256 20121207T000000Z 20121207/us-east-1/redshift/aws4_request 06b6bef4f4f060a5558b60c627cc6c5b5b5a959b9902b5ac2187be80cbac0714

The first line of the string to sign is the algorithm, the second line is the time stamp, the third line is the credential scope, and the last line is a hash of the canonical request from Task 1: Create a Canonical Request. The service name to use in the credential scope is redshift.

For Task 3: Create a Signature, the derived key can be represented as:

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derived key = HMAC(HMAC(HMAC(HMAC("AWS4" + YourSecretAccessKey,"20121207"),"us-east-1"),"redshift"),"aws4_request")

The derived key is calculated as series of hash functions. Starting from the inner HMAC statement in the formula above, you concatenate the phrase "AWS4" with your secret access key and use this as the key to hash the data "us-east-1". The result of this hash becomes the key for the next hash function.

After you calculate the derived key, you use it in a hash function that accepts two input strings, your string to sign and the derived key. For example, if you use the secret access key wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY and the string to sign given earlier, then the calculated signature is as follows:

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9a6b557aa9f38dea83d9215d8f0eae54100877f3e0735d38498d7ae489117920

The final step is to construct the Authorization header. For the demonstration access key AKIAIOSFODNN7EXAMPLE, the header (with line breaks added for readability) is:

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Authorization: AWS4-HMAC-SHA256 Credential=AKIAIOSFODNN7EXAMPLE/20121207/us-east-1/redshift/aws4_request, SignedHeaders=content-type;host;x-amz-date, Signature=9a6b557aa9f38dea83d9215d8f0eae54100877f3e0735d38498d7ae489117920