Ethereum: How to make signed API call in Swift

Creating Signed API Calls in Swift: Understanding HMAC-SHA256

As a developer, you are probably familiar with the importance of authentication and security in your API. One of the essential aspects is generating signatures for requests to verify authenticity and prevent tampering. In this article, we will explore how to create signed API calls using Swift and HMAC-SHA256.

What is HMAC-SHA256?

HMAC-SHA256 (Keyed-Hash Message Authentication Code with SHA-256) is a cryptographic algorithm that combines a secret key with a message (in our case, the encrypted request data) to create a fixed-size signature. This signature can be used for authentication and verification purposes.

Creating a Signed Request in Swift

To create a signed API call, you need to:

• Encode the Request Data: Create an encoded representation of the request data using a library such as Data or a custom implementation.

• Generate Secret Key: Use a secure method (e.g. using the ‘secrets’ framework) to generate a private key for signing.

• Create Signature: Use the HMAC-SHA256 algorithm to compute a digital signature based on your encoded request data and secret key.

Code Example: Signed API Call in Swift

Import Foundation
class EthereumAPI {
let apiKey = "your_api_key"
let apiSecret = "your_api_secret"
func signedRequest(_ requestData: [String: String]) -> ([String: String], Data) {
// Encode the request data
guard let encodedData = try? JSONEncoder().encode(requestData) else { return [], Data()}
// Generate the secret key using the secret system
let secretKey = try! SecretKey.generate(apiKey: apiKey, apiSecret: apiSecret)
// Generate a signature based on the HMAC-SHA256 algorithm
guard allow signature = hmacSHA256(secretKey, encodedData) else { return [], Data()}
// Returns the request data and the signature as an array of tuples
return [("code": -1022), ("msg": "Signed request"), ("signature": signature)], encodeddata
}
}

Explanation

In this example:

• First, we encode the request data using JSONEncoder.

• We generate the secret key using SecretKey.generate, which is the key issued by the API.

• We generate a signature based on the HMAC-SHA256 algorithm, passing in the encoded request data and our secret key.

• Finally, we return the original request data with the signed signature as a tuple string.

Usage Example

let api = EthereumAPI()
let requestData = ["code": -1022, "msg": "Verification request"]
let (signedRequest, signature) = try? api.signedRequest(requestData)
print("Signed request: \(signed request)")

This will output the original request data with a signed HMAC-SHA256 signature.

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