Last Updated : 31 Aug, 2021
HMAC (Hash-based Message Authentication Code) is a type of a message authentication code (MAC) that is acquired by executing a cryptographic hash function on the data (that is) to be authenticated and a secret shared key. Like any of the MAC, it is used for both data integrity and authentication. Checking data integrity is necessary for the parties involved in communication. HTTPS, SFTP, FTPS, and other transfer protocols use HMAC. The cryptographic hash function may be MD-5, SHA-1, or SHA-256. Digital signatures are nearly similar to HMACs i.e they both employ a hash function and a shared key. The difference lies in the keys i.e HMACs use symmetric key(same copy) while Signatures use asymmetric (two different keys).
History
Processes and decisions pertinent to business are greatly dependent on integrity. If attackers tamper this data, it may affect the processes and business decisions. So while working online over the internet, care must be taken to ensure integrity or least know if the data is changed. That is when HMAC comes into use.
Applications
- Verification of e-mail address during activation or creation of an account.
- Authentication of form data that is sent to the client browser and then submitted back.
- HMACs can be used for Internet of things (IoT) due to less cost.
- Whenever there is a need to reset the password, a link that can be used once is sent without adding a server state.
- It can take a message of any length and convert it into a fixed-length message digest. That is even if you got a long message, the message digest will be small and thus permits maximizing bandwidth.
Working of HMAC
HMACs provides client and server with a shared private key that is known only to them. The client makes a unique hash (HMAC) for every request. When the client requests the server, it hashes the requested data with a private key and sends it as a part of the request. Both the message and key are hashed in separate steps making it secure. When the server receives the request, it makes its own HMAC. Both the HMACS are compared and if both are equal, the client is considered legitimate.
The formula for HMAC:
HMAC = hashFunc(secret key + message)
There are three types of authentication functions. They are message encryption, message authentication code, and hash functions. The major difference between MAC and hash (HMAC here) is the dependence of a key. In HMAC we have to apply the hash function along with a key on the plain text. The hash function will be applied to the plain text message. But before applying, we have to compute S bits and then append it to plain text and after that apply the hash function. For generating those S bits we make use of a key that is shared between the sender and receiver.
Using key K (0 < K < b), K+ is generated by padding O’s on left side of key K until length becomes b bits. The reason why it’s not padded on right is change(increase) in the length of key. b bits because it is the block size of plain text. There are two predefined padding bits called ipad and opad. All this is done before applying hash function to the plain text message.
ipad - 00110110 opad - 01011100
Now we have to calculate S bits
K+ is EXORed with ipad and the result is S1 bits which is equivalent to b bits since both K+ and ipad are b bits. We have to append S1 with plain text messages. Let P be the plain text message.
S1, p0, p1 upto Pm each is b bits. m is the number of plain text blocks. P0 is plain text block and b is plain text block size. After appending S1 to Plain text we have to apply HASH algorithm (any variant). Simultaneously we have to apply initialization vector (IV) which is a buffer of size n-bits. The result produced is therefore n-bit hashcode i.e H( S1 || M ).
Similarly, n-bits are padded to b-bits And K+ is EXORed with opad producing output S2 bits. S2 is appended to the b-bits and once again hash function is applied with IV to the block. This further results into n-bit hashcode which is H( S2 || H( S1 || M )).
Summary:
- Select K.
If K < b, pad 0’s on left until k=b. K is between 0 and b ( 0 < K < b ) - EXOR K+ with ipad equivalent to b bits producing S1 bits.
- Append S1 with plain text M
- Apply SHA-512 on ( S1 || M )
- Pad n-bits until length is equal to b-bits
- EXOR K+ with opad equivalent to b bits producing S2 bits.
- Append S2 with output of step 5.
- Apply SHA-512 on step 7 to output n-bit hashcode.
Advantages
- HMACs are ideal for high-performance systems like routers due to the use of hash functions which are calculated and verified quickly unlike the public key systems.
- Digital signatures are larger than HMACs, yet the HMACs provide comparably higher security.
- HMACs are used in administrations where public key systems are prohibited.
Disadvantages
- HMACs uses shared key which may lead to non-repudiation. If either sender or receiver’s key is compromised then it will be easy for attackers to create unauthorized messages.
Next
Message Authentication Codes
Share your thoughts in the comments
Please Login to comment...
FAQs
HMAC algorithm stands for Hashed or Hash-based Message Authentication Code. It is a result of work done on developing a MAC derived from cryptographic hash functions. HMAC is a great resistance towards cryptanalysis attacks as it uses the Hashing concept twice.
What is HMAC hash-based message authentication code? ›
Hash-based message authentication code (or HMAC) is a cryptographic authentication technique that uses a hash function and a secret key. With HMAC, you can achieve authentication and verify that data is correct and authentic with shared secrets, as opposed to approaches that use signatures and asymmetric cryptography.
What is the HMAC authentication key? ›
An HMAC key is a type of credential associated with an account, typically a service account. You use an HMAC key to create signatures using the HMAC-SHA256 signing algorithm. The signatures you create are then included in requests to the Cloud Storage XML API.
What is the HMAC SHA algorithm? ›
HMAC is a message authentication code (MAC) using a hash function. It combines with any cryptographic hash function, for example, md5, sha1, sha256. Hash function is wrapped to a class as one template parameter in HMAC and the wrapper class only has a static function involving the hash function.
What is the difference between hash and HMAC? ›
A message authentication code (MAC) is similar to a cryptographic hash, except that it is based on a secret key. When secret key information is included with the data that is processed by a cryptographic hash function, the resulting hash is known as an HMAC.
What is the primary difference between a hash and hashed message authentication code HMAC )? ›
A hash lets you verify only the authenticity of the data (i,. e., that the data you received is what was originally sent). An HMAC lets you verify both the authenticity and the originator of the data. A hash doesn't use a key.
What are the benefits of HMAC authentication? ›
Ultimately, HMAC provides a great layer of security for companies that have sensitive data that needs protecting. It's an important measure to protect data integrity from attackers and offers a clear indication if data has been compromised. See how Kinde compares to other authentication providers.
What is the best practice of HMAC authentication? ›
3 Best practices for HMAC
To use HMAC effectively and securely, it's recommended to use a strong hash function, such as SHA-256, SHA-384, or SHA-512. A secure key should be generated randomly, stored securely, and rotated periodically. The key should be long enough to prevent brute-force attacks.
What is signing with HMAC authentication? ›
HMAC Signing is an access token method that adds another level of security by forcing the requesting client to also send along a signature that identifies the request temporally to ensure that the request is from the requesting user, using a secret key that is never broadcast over the wire.
Why do we need HMAC authentication in Web API? ›
HMAC (hash-based message authentication code) is used to verify that a request is coming from an expected source and that the request has not been tampered with in transit.
HMAC does not encrypt the message. Instead, the message (encrypted or not) must be sent alongside the HMAC hash. Parties with the secret key will hash the message again themselves, and if it is authentic, the received and computed hashes will match.
What is the use of message authentication code? ›
Message Authentication Code (MAC), also referred to as a tag, is used to authenticate the origin and nature of a message. MACs use authentication cryptography to verify the legitimacy of data sent through a network or transferred from one person to another.
What is the difference between HMAC and JWT? ›
A JWT (when using HMAC as the signing scheme) is basically just an HMAC message where the message data is a JSON object. The interesting thing about the JWT system is that the sender and the receiver of the JWT are typically the same entity, that is, the webserver.
What are the disadvantages of HMAC? ›
One of the main drawbacks of HMAC is that it requires both parties to share a secret key in advance, which can be challenging in some scenarios, such as public key infrastructures or distributed systems.
How to generate HMAC secret key? ›
Create an HMAC key
- In the Google Cloud console, go to the Cloud Storage Settings page. Go to Settings.
- Select the Interoperability tab.
- Click add_box Create a key for a service account.
- Select the service account you want the HMAC key to be associated with.
- Click Create key.
You can't decode it as it's a one way encryption. To validate you need to recreate the the HMAC_SHA256 on your side from the data that has been passed and a shared secret key. You then compare your calculated value to one provided and if they match you know the data hasn't been tampered with.
How is the hash message authentication code HMAC algorithm used in an ipsec VPN? ›
Here is how an HMAC works, in its simplest form. First, both the server and the client agree to use the same cryptographic hash function (SHA-384) and establish a shared secret key. Then, the sender combines that shared secret key with the data being sent and creates a hash out the combination of the two.
What is the HMAC OTP algorithm? ›
Time-based one-time password (TOTP) is a computer algorithm that generates a one-time password (OTP) using the current time as a source of uniqueness. As an extension of the HMAC-based one-time password algorithm (HOTP), it has been adopted as Internet Engineering Task Force (IETF) standard RFC 6238.
What type of message authentication code uses hashing? ›
HMAC. With a Keyed-Hash Message Authentication Code (HMAC) system, a one-way hash is used to create a unique MAC value for every message sent. The input parameters can have various values assigned, and making them very different from each other may produce a higher level of security.
What is HMAC SHA-384? ›
HMACSHA384 is a type of keyed hash algorithm that is constructed from the SHA-384 hash function and used as a Hash-based Message Authentication Code (HMAC). The HMAC process mixes a secret key with the message data and hashes the result. The hash value is mixed with the secret key again, and then hashed a second time.
