Elements of an AWS API request signature - AWS Identity and Access Management

Elements of an AWS API request signature


Unless you are using the AWS SDKs or CLI, you must write code to calculate signatures that provide authentication information in your requests. Signature calculation in AWS Signature Version 4 can be a complex undertaking, and we recommend that you use the AWS SDKs or CLI whenever possible.

Each HTTP/HTTPS request that uses Signature Version 4 signing must contain these elements.

Endpoint specification

Specifies the DNS name of the endpoint to which you send the request. This name usually contains the service code and the Region. For example, the endpoint for Amazon DynamoDB in the us-east-1 Region is dynamodb.us-east-1.amazonaws.com.

For HTTP/1.1 requests, you must include the Host header. For HTTP/2 requests, you can include the :authority header or the Host header. Use only the :authority header for compliance with the HTTP/2 specification. Not all services support HTTP/2 requests.

For the endpoints supported by each service, see Service endpoints and quotas in the AWS General Reference.


Specifies an API action for the service. For example, the DynamoDB CreateTable action or the Amazon EC2 DescribeInstances action.

For the actions supported by each service, see the Service Authorization Reference.

Action parameters

Specifies the parameters for the action specified in the request. Each AWS API action has a set of required and optional parameters. The API version is usually a required parameter.

For the parameters supported by an API action, see the API Reference for the service.


Specifies the date and time of the request. Including the date and time in a request helps prevent third parties from intercepting your request and resubmitting it later. The date that you specify in the credential scope must match the date of your request.

The time stamp must be in UTC and use the following ISO 8601 format: YYYYMMDDTHHMMSSZ. For example, 20220830T123600Z. Do not include milliseconds in the time stamp.

You can use a date or an x-amz-date header, or include x-amz-date as a query parameter. If we can't find an x-amz-date header, then we look for a date header.

Authentication information

Each request that you send must include the following information. AWS uses this information to ensure the validity and authenticity of the request.

  • Algorithm – Use AWS4-HMAC-SHA256 to specify Signature Version 4 with the HMAC-SHA256 hash algorithm.

  • Credential – A string that consists of your access key ID, the date in YYYYMMDD format, the Region code, the service code, and the aws4_request termination string, separated by slashes (/). The Region code, service code, and termination string must use lowercase characters.

  • Signed headers – The HTTP headers to include in the signature, separated by semicolons (;). For example, host;x-amz-date.

  • Signature – A hexadecimal-encoded string that represents the calculated signature. You must calculate the signature using the algorithm that you specified in the Algorithm parameter.