What is an API key and how can you use it securely

API and API Keys

To understand API keys, it's important to first examine APIs themselves. An Application Programming Interface (API) is a software intermediary that enables information exchange between two or more applications. For example, APIs from various data platforms allow other applications to retrieve and utilize cryptocurrency data such as price, volume, and market capitalization.

An API key can be a single key or a set of multiple keys. Different systems use these keys for authenticating and authorizing applications, much like usernames and passwords. API clients use API keys to authenticate the application making the API call.

For example, if an application wants to access a data platform's API, the platform generates an API key and uses it to authenticate the requesting application (the API client). When the application sends a request to the platform's API, the API key is included with the request.

In this scenario, only the authorized application should use the API key, and it must not be shared with third parties. Sharing the API key enables a third party to access the API and perform actions as the authorized application.

Additionally, the platform’s API can use the API key to verify that the application is authorized to access the requested resource. API owners can also leverage API keys to monitor API activity, including request types, traffic, and volume.

What Is an API Key

An API key is used to control and track who accesses an API and how it is used. The term “API key” can refer to different things, depending on the system. Some systems issue a single code, while others may issue multiple codes for one API key.

In essence, an API key is a unique code or set of unique codes that APIs use to authenticate and authorize the calling user or application. Some codes are for authentication, while others create cryptographic signatures that verify request legitimacy.

These authentication codes are called "API keys," while codes for generating cryptographic signatures are known as “secret key,” “public key,” or “private key.” Authentication identifies and verifies involved parties.

Authorization, in turn, determines which API services can be accessed. An API key functions much like an account’s username and password, and can be paired with additional security features to enhance protection.

The API owner generates each API key specifically for a designated entity, and each time an API endpoint is called that requires user authentication or authorization, the appropriate key is used.

Cryptographic Signatures

Certain API keys employ cryptographic signatures as an extra layer of verification. When a user submits data to an API, a digital signature generated by another key can be added to the request. Using cryptography, the API owner can validate that the signature matches the transmitted data.

Symmetric and Asymmetric Signatures

Cryptographic keys used to sign data sent through APIs generally fall into two categories:

Symmetric Keys

Symmetric keys use a single secret key for both signing data and verifying the signature. In this model, the API owner generates both the API key and the secret key, which API services use to verify the signature. The main advantage of a single key is faster signature generation and verification, with reduced computational overhead. HMAC is a widely used example of a symmetric key system.

Asymmetric Keys

Asymmetric keys involve a pair of keys: a private key and a public key, which are distinct but cryptographically linked. The private key generates the signature, while the public key verifies it. The API owner generates the API key, while the user generates their own private and public key pair. The API owner uses only the public key for signature verification, while the private key remains confidential.

The primary benefit of asymmetric keys is heightened security, as signature creation and verification are separated. This lets external systems verify signatures without exposing the signing process. Some asymmetric encryption systems also support adding passwords to private keys. A common example is an RSA key pair.

API Key Security

The user is responsible for API key security. API keys function as passwords and require the same level of caution. Never share your API key with third parties, as doing so is equivalent to sharing your password and can put your account at risk.

API keys are frequent targets for cyberattacks since they enable critical operations like accessing personal information or conducting financial transactions. There have been incidents where attackers have breached online code repositories and stolen API keys.

If API keys are stolen, this can lead to serious consequences and substantial financial losses. Some API keys do not expire, so attackers may continue using them until they’re revoked.

API Key Security Best Practices

Because API keys provide access to sensitive data, secure usage is essential. Follow these best practices for robust API key management:

1. Rotate API Keys Regularly

Regularly rotate API keys. To do so, delete the current API key and create a new one. For environments with multiple systems, deleting and generating API keys is straightforward. Just as some systems require password changes every 30–90 days, API key owners should rotate keys on a similar schedule when possible.

2. Use IP Whitelisting

When creating a new API key, specify a list of authorized IP addresses (IP whitelist). You may also define a list of blocked IP addresses (IP blacklist). If a key is compromised, unauthorized IPs won’t be able to use it.

3. Use Multiple API Keys

Issuing multiple keys for different tasks reduces risk, as your account security doesn’t rely on a single key. You can also assign distinct IP whitelists for each key, greatly improving your security posture.

4. Store API Keys Securely

Never store keys in public locations, on shared computers, or as plain text. To enhance security, use encryption or a secrets management service for each key, and take care to avoid accidental disclosure.

5. Never Share Your API Keys

Sharing your API key is equivalent to sharing your password. Doing so gives third parties the same authentication and authorization as you. If a data breach occurs, stolen API keys can be used to compromise your account. Only you and the generating system should use your API key.

If your API key is compromised, immediately revoke or disable it to prevent further damage. If you suffer financial losses, document key information about the incident and contact relevant organizations as well as law enforcement to increase your chances of recovering lost assets.

Conclusion

API keys serve authentication and authorization roles, so users must store them securely and use them cautiously. Multiple layers and strategies exist for securing API keys. Always treat your API key as you would your account password.

FAQ

What is an API key and what is its purpose?

An API key is a unique code for authenticating and managing access to a programming interface. It ensures security and enforces user permissions for the API, preventing unauthorized access.

How do you securely store an API key in an application?

Store API keys in encrypted form using environment variables or configuration files with restricted access. Never embed keys in source code. Use a secrets manager to automate encryption and decryption at runtime.

What are the risks and security threats of API key leaks?

API key leaks can lead to unauthorized account access, theft of funds, total account takeover, and unauthorized transactions. Attackers may access sensitive data, alter security settings, and cause significant financial losses.

How do you restrict permissions and access rights for API keys?

Grant only the minimum permissions required for your API keys by following the principle of least privilege. Regularly review and update permissions for optimal security.

What should you do if your API key is compromised or stolen?

Immediately revoke or disable your API key to prevent further misuse. Contact the API provider for further instructions. Promptly generate a new replacement key.