What Is an API Key?

What Is an API Key?

An API key is a unique code that allows an application programming interface (API) to identify the user or application that is calling it. By using API keys, one can monitor and control who is using the API and how they are using it. It serves a similar purpose as usernames and passwords but has a different form, sometimes consisting of a single key or multiple keys. To ensure optimal security against possible API key theft, users should follow best practices to stay protected from its associated effects.


To comprehend what an API key is, we must first recognize the concept of an API. An API, or Application Programming Interface, is a form of software intermediary that permits two or more programs to collaborate. For instance, CoinMarketCap's API allows different applications to access and utilize digital currency information, such as price, volume, and market cap.

An API key is an authentication tool that comes in various forms, ranging from a single key to a set of multiple keys. It is analogous to a username and password and is used by an API client to validate an application's access to an API. Through the use of this key, a given system is able to determine whether an app has the necessary authority to make a call to the API. API owners use API keys to observe API activity, including different types, levels, and volumes of requests.


An API key is a code that is used to identify and manage access to an API. Depending on the specific system, it can refer to a single code or multiple codes. The API key is used to control and monitor the use of the API, tracking who is making use of it and how.

An API key is a unique identifier used by an API to authenticate and authorize the user or application making the request. Authentication can be achieved through the use of codes, while the cryptographic signature of a request can be verified with a special set of codes.

Authentication generally involves identifying the entities involved and confirming their identities. These authentication codes are generally referred to as an "API key," while codes used for cryptographic signatures have different names, such as "secret key," "public key," or "private key."

Authorization defines which API services are allowed to be accessed. An API key works similarly to an account's username and password. It can be used to add extra security layers to the overall process.

An API key is unique for each entity that is authorized to make requests to an API endpoint. The appropriate key must be included when making an API call that requires authentication or authorization.

Cryptographic Signatures

Some API keys are equipped with cryptographic signatures to provide an extra degree of protection. When a user needs to send data to an API, they can attach a digital signature created with a different key. Cryptography enables the API provider to evaluate the digital signature in comparison to the data sent to ensure accuracy.

Symmetric and Asymmetric Signatures 

Data shared through an API can be verified with cryptographic keys that fall into the following categories:

Symmetric Keys

Symmetric key cryptography uses one secret key to both sign data and verify signatures. In this case, the API key and secret key are usually generated by the API owner, and the API service must use the same secret key for signature verification. Because the same key is used, symmetric key cryptography is faster since less computation is needed to generate and verify the signature. HMAC is a good example of a symmetric key.

Asymmetric Keys

These require a pair of keys: one private and one public. The private key is used to generate the signature, while the public key is used to verify the signature. The owner of the API generates the API key, while the user is responsible for generating the private/public key pair. The public key is the only key that needs to be shared with the API owner, while the private key remains secure and local to the user.

The use of asymmetric keys provides increased security due to the separation of signature generation and verification. This means that third-party systems are capable of verifying signatures without having the ability to create them. Additionally, certain forms of asymmetric encryption can offer improved protection by adding a password to private keys. An example of this is an RSA key pair.

Is an API Key a Secure Method of Authentication?

As a user, you are responsible for managing your API key correctly. It should be treated with the same level of care as a password, as it essentially works the same way. Never share your API key with anyone else, as doing so could endanger your account.

API keys are a very attractive target for cybercriminals, as these can be utilized to take sensitive actions on systems, like asking for confidential information or conducting financial transactions. Sadly, instances of web crawlers successfully invading code repositories on the web to obtain API keys have been reported.

API key theft can be extremely damaging and can result in extensive financial damage. Additionally, API keys that never expire give the perpetrators of the theft the ability to use them for an indefinite amount of time before they can be revoked.

Tips for Properly Utilizing API Keys

It is essential to take measures to protect API keys, as they provide access to sensitive data and can easily be exploited. To maximize their overall security, adhere to the following best practice guidelines when using API keys:

  1. If feasible, API keys should be updated regularly. This entails removing your present API key and creating a new one. With multiple systems, it's straightforward to make and delete API keys. As some systems need you to reset your password every 30 to 90 days, API keys should be cycled through with a similar frequency, if possible.
  2. To help prevent your API key from being accessed by unapproved parties, create a whitelist of IP addresses that are authorized to use your key. You can also create a blacklist with IPs that you specifically want to restrict from accessing your key. With an IP whitelist and blacklist in place, even if your API key is stolen, it cannot be accessed from an unrecognized IP address.
  3. By creating multiple API keys and assigning each key to a specific task, you can minimize the risk of an unauthorized user gaining access to your system. Additionally, you can limit access to each key by implementing IP whitelisting, thus further limiting the potential risk of a breach.
  4. Ensure the secure keeping of your API keys by avoiding storing them in public areas, public computers, or in a plain text format. Utilize encryption or a secret manager to safeguard each of your keys, and be vigilant when handling them to prevent accidental exposure.
  5. To ensure the security of your account, do not share your API key with anyone. Doing so will enable the other party to gain the same level of access and authorization as you, which could lead to your API key getting stolen in a security vulnerability. Keep your API key between yourself and the system that approves it, and do not share it with outsiders.

If your API key is exposed, it's important to act fast. Disable it immediately to minimize any further risk. Additionally, collect evidence, such as screenshots of any documents related to the incident, and contact the applicable organizations. Finally, filing a police report increases your chance of recovering any losses.


API keys are essential for maintaining secure authentication and authorization processes, so users must take the utmost care in managing and protecting them. Securing API keys involves considering various aspects and layers. To keep their accounts secure, users should treat their API key like a password.

Symmetric Keys
Asymmetric Keys
Cryptographic Keys
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