HMAC consists of twin benefits of Hashing and. HMAC, as noted, relies on a hash. b) Statement is incorrect. It takes a single input -- a message -- and produces a message digest, often called a hash. g. But it also provides unforgeability. HMAC has a cryptographic hash function H and a secret key K. The server receives the request and regenerates its own unique HMAC. The parameters key, msg, and digest have the same meaning as in new(). . 03-16-2020 05:49 AM. Data are taken in blocks of length L 64 bytes (Mineta et al. Unit -1 Cryptography | Symmetric, Block & Stream Cipher, AES, DES, RC4, Modes of Block Cipher -2 Asymmetric Cryptography | H. from hmac import compare_digest. #inte. HMACSHA512 is a type of keyed hash algorithm that is constructed from the SHA-512 hash function and used as a Hash-based Message Authentication Code (HMAC). CMAC is a block-cipher mode of operation that is commonly used with AES (Advanced Encryption Standard) and 3DES (Triple Data Encryption Standard) algorithms. It is my understanding that HMAC is a symmetric signing algorithm (single secret key) whereas RSA is an asymmetric signing algorithm (private/public key pair). The man page says this about it: Authenticated encryption with AES in CBC mode using SHA256 (SHA-2, 256-bits) as HMAC, with keys of 128 and 256 bits. This property of mapping signif-icantly accelerates the learning process of CMAC, which is considered a main advantage of it comparing to other neural network models. 1 Answer. AES-GCM vs. Alternatives to HMAC-MD5 include HMAC-SHA256 [HMAC] [HMAC-SHA256] and [AES-CMAC] when AES is more readily available than a. . The key should be randomly generated bytes. Message authentication code. ) Uses shared symmetric key to encrypt message digest. To replace a given hash function in an HMAC implementation, all that is required is to remove the existing hash function module and drop in the new module. For help with choosing a type of KMS key, see Choosing a KMS key type. Here is a table showing the differences of the possibilities for each primitive: Feature. The HMAC and CMAC key types are implemented in OpenSSL's default and FIPS providers. HMAC Authentication. HMAC can be used with any iterative cryptographic hash function, e. This value Created by Ciphertext + Key = Message Authentication Code. If you use AES as "KDF" in this way, it is equivalent to sending an AES-ECB encrypted key that the recipient decrypts. Think of HMAC as an extension to what MAC is able to do. hexdigest ()) The output is identical to the string you seen on wiki. Full Course: Authentication Codes (MACs). Java Mac HMAC vs C++ OpenSSL hmac. The hash value is mixed with the secret key again, and then hashed a second time. Unlike the previous authentication methods there isn’t, as far as I can tell a. Cryptographic algorithm validation is a prerequisite of cryptographic module validation. At the risk of being overly reductionist, AES-SIV is basically a nonce misuse resistant variant of AES-CCM: Where AES-CCM uses CBC-MAC, AES-SIV uses CMAC, which is based on CBC-MAC but with a doubling step (left shift then XOR with the round constant). One construction is HMAC and it uses a hash function as a basic building block. It then compares the two HMACs. 58. This can be seen from the code. The NIST provides test vectors in NIST: Block Cipher Modes of Operation - CMAC Mode for Authentication for AES128, AES192, and AES256. Cryptography is the process of securely sending data from the source to the destination. The fundamental difference between the two calls are that the HMAC can only. This module implements the HMAC algorithm. 1 on the mailing list. 01-24-2019 11:39 AM. hmac. A (digital) signature is created with a private key, and verified with the corresponding public key of an asymmetric key-pair. From the description of CMAC and HMAC, given the key and the tag, I think it is easy to derive the CMAC message than the HMAC message. 03-16-2020 05:49 AM. How to calculate a hmac and cmac. For information about creating multi-Region HMAC KMS keys, see Multi-Region keys in AWS KMS. CMAC: CMAC is a type of message authentication code that is based on a block cipher. Are they the same? Yes, you might check that following way. Cryptography and Network Security Chapter 12 Fourth Edition by William Stallings Lecture slides by Lawrie Brown. By which I mean I have to put a bunch of values together and HMAC-SHA1 encrypt them. Yes, HMAC is more complex than simple concatenation. So I guess the question is: are there any known algorithms - such as Grover's algorithm - that would significantly bring down the security of HMAC-SHA256 assuming a. A (digital) signature is created with a private key, and verified with the corresponding public key of an asymmetric key-pair. A subset of CMAC with the AES-128 algorithm is described in RFC 4493. 0, which is available in Master. Instead of a single key shared by two participants, a public-key cipher uses a pair of related keys, one for encryption and a different one for decryption. The advantage of utilizing a hash-based MAC rather than a MAC-based a. HMAC is a widely used cryptographic technology. Both AES and SHA-2 performance. And of course any common MAC can be used in the same role as HMAC, as HMAC is just a MAC after all. 1. A cipher block size of 128 bits (like for AES) guarantees that the. MAC techniques are studied which are CBC-MAC, XMAC, CMAC, and HMAC. We use SHA1 because it is available on XP and above, though we would prefer SHA-256 or a CMAC. MAC address is defined as the identification number for the hardware. This is going to be a long question but I have a really weird bug. Java vs Python HMAC-SHA256 Mismatch. The number of blocks is the smallest integer value greater than or equal to the quotient determined by dividing the length parameter by the block length, 16 octets. The attack needs 297 queries, with a success probability 0. ∙Message encryption. CRC64 vs an 8-byte (64-bit) truncated HMAC or CRC32 vs a 4-byte (32-bit) truncated HMAC. The main difference in MACs and digital signatures is that, in digital signatures the hash value of the message is encrypted with a user’s public key. 3: MD5 (K + T + K) seems preferable to both T+K and K+T, and it also makes bruteforcing. g. compare_digest is secrets. Officially there are two OMAC algorithms (OMAC1 and OMAC2) which are both essentially the same except for a small tweak. It's just that you have swapped the direction of encryption and decryption for AES. In short: public class HMACSHA256 : HMAC {. To resume it, AES-CMAC is a MAC function. Learn more about message authentication. 1. View the full answer. HMAC has several advantages over other symmetric MACs, such as CBC-MAC, CMAC, or GMAC. . NIST SP 800-90A ("SP" stands for "special publication") is a publication by the National Institute of Standards and Technology with the title Recommendation for Random Number Generation Using Deterministic Random Bit Generators. CMAC NN, it is found that CMAC is a competitive intelligent controller used in modeling, identification, classification, compensation and for nonlinear control. hexkey:. In most cases HMAC will work best, but CMAC may work better where there is embedded hardware which has hardware accelleration for block ciphers. Compute HMAC/SHA-256 with key Km over the concatenation of IV and C, in that order. If understood right, CMAC is not quantum-safe because it relies on AES-128 (which isn't considered as quantum-safe), while HMAC is, because it relies on SHA3 (which is considered as quantum-safe). The HMAC verification process is assumed to be performed by the application. So, will CBC solve my purpose. . In most cases HMAC will work best, but CMAC may work better where there is embedded hardware which has hardware. CMAC Block Cipher-based MAC Algorithm CMACVS CMAC Validation System FIPS Federal Information Processing Standard h An integer whose value is the length of the output of the PRF in bits HMAC Keyed-Hash Message Authentication Code . Cipher Based MAC (CMAC) and 2. . HMAC Algorithm • HMAC consists of twin benefits of Hashing and MAC, and thus is more secure than any other authentication codes. Second, what exactly is HMAC and how does it differ from Mac? HMAC is more secure than MAC because the key and message are hashed separately. Additionally the Siphash and Poly1305 key types are implemented in the default provider. In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a secret cryptographic key. Other EVP update functions are called things like EVP_SignUpdate, EVP_VerifyUpdate, EVP_OpenUpdate, EVP_SealUpdate, EVP_DigestUpdate, EVP_CipherUpdate. I've checked and I can confirm that your results can be obtained if we concatenate opad with hex-encoded hash. g. 12. How to. Hash-based MAC (HMAC). Hash-based message authentication code (HMAC) is a mechanism for calculating a message authentication code involving a hash function in combination with a secret key. It doesn't apply simply because the adversary doesn't hold the secret key and can therefore not try to create collisions. For HMAC, it is difficult. Hash Based Message Authentication Code, HMAC, is an essential piece for. 1. While MAC algorithms perform a direct calculation, HMAC involves an additional step of. Yes, creating a hash over the key is actually a common method of creation of KCV's (outside of encrypting a block of zero bytes). As you can see, I have taken the example posted here: How to calculate AES CMAC using OpenSSL? which uses the CMAC_Init/Update/Final interfaces of OpenSSL and tried various NIST values to check if. HMAC itself does not use the AES algorithm in any way (the AES-CMAC algorithm does but that algorithm requires an additional key). University Institute of Engineering (UIE)The significant difference between MAC and hash (HMAC here) is the dependence on a key. 9340 is way way larger than 340. by encrypting an empty plaintext with the. To examine the difference in the default key policy that the AWS. hmac = enc [-32:] cipher_text = enc [16:-32] The CFB mode is actually a set of similar modes. hmac. /foo < foo. 3. On receiver’s side, receiver also generates the code and compares it with what he/she received thus ensuring the originality of the message. The main difference is that an HMAC uses two rounds of hashing instead of. HMAC has several advantages over other symmetric MACs, such as CBC-MAC, CMAC, or GMAC. Understanding the Difference Between HMAC and CMAC: Choosing the Right Cryptographic Hash FunctionIn this tutorial, we’ll learn about Hash and MAC functions and the differences between them. We look at two MACs that are based on the use of a block cipher mode of operation. CMAC. The pair of keys is "owned" by just one participant. provide a way to make sure the message has not been tampered, are "secured" by a secret, but symmetric key. digest (key, msg, digest) ¶ Return digest of msg for given secret key and digest. There are some technical contexts where a MAC is sufficient (e. So you need tell pycrypto to use the same mode as in CryptoJS:Difference in HMAC signature between python and java. An HMAC function is used by the message sender to produce a value (the MAC) that is formed by condensing the secret key and the message input. Hash-based message authentication code, or HMAC, is an important building block for proving that data transmitted between the components of a system has not been tampered with. The NIST provides test vectors in NIST: Block Cipher Modes of Operation - CMAC Mode for Authentication for AES128, AES192, and AES256. I am all for securing the fort, however HMAC solution presents one problem - its more complicated and requires developer to firstly create HMAC and then feed it into a request,. Concatenate IV, C and M, in that order. compare_digest) outputs. From the viewpoint of hardware realization, the major differences between the CCMAC and HCMAC are those listed in Table 1. As with any MAC, it may be used to simultaneously verify both the data integrity. The Difference Between HMAC and CMAC: Exploring Two Cryptographic Hash FunctionsMACs can be created from unkeyed hashes (e. Here is the code. The advantage of. While MAC algorithms perform a direct calculation, HMAC involves an additional step of applying the hash function twice. One possible reason for requiring HMAC specifically, as opposed to just a generic MAC algorithm, is that the. HMAC objects take a key and a HashAlgorithm instance. First of all, you are correct in that GMAC requires an IV, and bad things happen if a particular IV value is reused; this rather rules out GMAC for some applications, and is a cost. MAC. When people say HMAC-MD5 or HMAC-SHA1 are still secure, they mean that they're still secure as PRF and MAC. crypto. In general, the network interface cards (NIC) of each computer such as Wi-Fi Card, Bluetooth or Ethernet Card has unchangeable MAC address embedded by the vendor at the time of manufacturing. I have written this code? It is not advisable to use the same key for encryption and HMAC, or in short for two different purposes. It is not something you would want to use. This produces R and S integers (the signature). AES-SIV is MAC then encrypt (so is AES-CCM). A MAC is also called a keyed hash. You can use an CMAC to verify both the integrity and authenticity of a message. Improve this answer. 1 messages with a success rate of 0. 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. HMAC stands for hybrid message authentication code. There are different researches done. 1. So really, choosing between SHA1 and SHA256 doesn't make a huge difference. CMAC uses a block cipher to generate the hash, while HMAC uses a cryptographic hash function. 3. To summarize the key differences between hashing and HMAC: Conceptual Difference: Hashing guarantees the integrity of data, while HMAC ensures integrity and authentication. H. It is due to by the inner. As with any MAC, it may be used to simultaneously. This module implements the HMAC algorithm. 1. • The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key. hexdigest ()) The output is identical to the string you seen on wiki. Any cryptographic hash function, such as SHA-2 or SHA-3, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-X, where X is the hash function used (e. AES (Advanced_Encryption_Standard) is a symmetric encryption standard. First, HMAC can use any hash function as its underlying algorithm, which means it can leverage the security. crypto. The only difference apart from the output size is that these special. . $egingroup$ SHA-3 can be computed in parallel, is faster than SHA-256, and doesn't even require HMAC for security (simple message concatenation with key is secure). There is another way which is CBC-MAC and its improved version CMAC and is based on block ciphers. HMAC treats the hash function as a “black box. . Preneel and van Oorschot [] show some analytical advantages of truncating the output of hash-based MAC functions. If understood right, CMAC is not quantum-safe because it relies on AES-128 (which isn't considered as quantum-safe), while HMAC is, because it relies on SHA3 (which is considered as quantum-safe). Martin Törnwall. In new code, default to HMAC with a strong hash like SHA-256 or SHA-384. Only the holder of the private key can create this signature, and normally anyone knowing the public key. If they are the same, the message has not been changed Distinguish between HMAC and CMAC. HMAC Algorithm in Computer Network. SHA-256 is slow, on the order of 400MB/sec. The HMAC process mixes a secret key with the message data, hashes the result with the hash function, mixes that hash value with the secret key. But unlike the traditional MAC we talked about earlier, a hash-based message authentication code, or HMAC, is a type of MAC that uses two keys and hashes stuff twice. HMAC and NMAC based on MD5 without related keys, which distin-guishes the HMAC/NMAC-MD5 from HMAC/NMAC with a random function. HMAC will yield different results for each. ), where h() is a hash function. , FIPS-approved and NIST-recommended) cryptographic algorithms and their individual components. $egingroup$ Advantages of HMAC are speed, as stated in the fine answers; and small size of the authenticating token (128 bits or even much less, vs at least 1024 bits). It is similar to HMAC, but instead of using a hash function, it uses a block cipher to produce a MAC for a message. Full Course: Authentication Codes (MACs). Construction: HMAC is a hash-based construction, whereas CMAC is a cipher-based construction. The ASCII art picture above applies as well with the difference that only step (4) is used and the SKCIPHER block chaining mode is CBC. (Possible exception: Maybe on a tiny microcontroller you will have hardware support for HMAC-SHA256, but not for XSalsa20. HMAC-MD5 has b = 128 bits of internal state. The CF documentation for hmac is sorely lacking useful details. The AES cipher does normally not play a role in signing/verifying, unless it is used in a cipher based MAC algorithm such as the previously mentioned AES-CMAC algorithm. This Recommendation specifies techniques for the derivation of additional keying material from a secret key—either established through a key establishment scheme or shared through some other manner—using pseudorandom functions HMAC, CMAC, and KMAC. HMAC doesn't have that capability. CBC-MAC, CMAC, OMAC, and HMAC. keytab vdzharkov@VDZHARKOV. If you use HMAC, you will more easily find test vectors and implementations against which to test, and with which to. Obviously, just like a KCV created by encrypting zero's, you might want to make sure that it isn't used the same way in your protocol. Hash the result obtained in step 2 using a cryptographic hash function. Derive one or more keys from a master secret using the HMAC-based KDF defined in RFC5869. 6 if optimized for speed. The rfc4493 only provides a test code for AES128. With regard to the leading CPU architecture for PC's, there are the Intel whitepapers. In doing so, confidentiality protects data by making it unreadable to all but authorised entities, integrity protects data from accidental or deliberate manipulation by entities, authentication. CryptoJS only supports segments of 128 bit. . $ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc LD_LIBRARY_PATH=. For this, CMAC would likely run faster than HMAC. Available if BOTAN_HAS_CMAC is defined. ∙Hash Functions. Regarding the contrast of hash function and MAC, which of the following statements is true? Compared to hash function, MAC involves a secret key, but it is often not secure to implement a MAC function as h(k, . The CCMA test will cost about $100. At the risk of being overly reductionist, AES-SIV is basically a nonce misuse resistant variant of AES-CCM: Where AES-CCM uses CBC-MAC, AES-SIV uses CMAC, which is based on CBC-MAC but with a doubling step (left shift then XOR with the round constant). An HMAC also provides collision resistance. As of 1-1-2016, TDES KO2 encrypt is no longer compliant. g. Which MAC algorithm is faster - CBC based MAC's or HMAC - depends completely on which ciphers and hashes are used. B has to check whether the ciphertext. The hmac call gives you keyed hash of the string "data" using string "key" as the key and sha1 as the hash function. PRF is another common security goal. Contrary to you mentioning HMAC, GCM does use a MAC construction but it is called GMAC. The function is equivalent to HMAC(key, msg, digest). . So the term AES-HMAC isn't really appropriate. CMAC. TL;DR, an HMAC is a keyed hash of data. HKDF (master, key_len, salt, hashmod, num_keys = 1, context = None) ¶. What are advantages/disadvantages for using a CMAC that proofs the integrity and authenticity of a message but doesn't encrypt the payload itself? Why should it be used instead of symmetric encrypted payload and CRC (CRC is encrypted as well)? This could also proof authenticity, integrity AND confidentially. People also inquire as to what AES CMAC is. I'm trying to decrypt kerberos traffic with wireshark for the learning purposes. The benefit of using KMAC128 k ( m) instead of H ( k ‖ m) is that there is no danger of such colliding uses. . {{DocInclude |Name=Key and Parameter Generation |Url=The EVP functions support the ability to generate parameters and keys if required for EVP_PKEY. Cryptographic hash functions execute faster in software than block ciphers. The attacker has to be able to compute the full digest that the message already contains in addition to computing what the new digest value is meant to be. There are two types of Message Authentication Code (MAC): 1. This paper puts forward the idea of using advanced modes of operation of symmetric block ciphers to achieve confidentiality and authentication in one cryptographic operation. Cryptography is the process of sending data securely from the source to the destination. A good cryptographic hash function provides one important property: collision resistance. is taken as a filename, since it doesn't start with a dash, and openssl doesn't take options after filenames, so the following -out is also a filename. , MD5, SHA-1, in combination with a secret shared key. Both AES and SHA-2 performance can be. The HMAC and CMAC key types are implemented in OpenSSL's default and FIPS providers. CMAC. 1 Answer Sorted by: 3 DAA is a specific deprecated government standard for authenticated encryption. In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a secret cryptographic key. . With an HMAC, you can use popular hashing algorithms like SHA-256, etc with a secret key to generate a Message Authentication Code. . HMAC can be used in sequence with some iterated cryptographic hash function. As a naive example: sha256 ('thisIsASe' + sha256 ('cretKey1234' + 'my message here')) Which is a simplified version of the function given. This can provide validation. This refinement, adopted by NIST, is the C i pher-based Message Authent i cat i on Code (CMAC) mode of oper- ation for use with AES and triple DES. Digital signatures are the public key equivalent of private key message authentication codes (MACs). Anybody who has this key can therefore be a verifier and signer. There's actually a very big problem with SHA256 (key||data): SHA-256, along with SHA-512, SHA-1, MD5, and all other hashes using the Merkle–Damgård construction, is vulnerable to a length extension attack: given H (x), it's very simple to find H (x||y), even if you only know the length of x, because of how the. HMAC SHA; HMAC is a bit more complicated than the raw hash function, but for longer messages it is just a bit slower than the raw hash function. Cifra 's benchmark shows a 10x difference between their AES and AES-GCM, although the GCM test also included auth-data. For detecting small errors, a CRC is superior. The difference between the numbers of clock cycles, taken by the two algorithms, is not large. The basic idea is to generate a cryptographic hash of the actual data. g. Whining about coding sins since 2011. . Only the holder of the private key can create this signature, and normally anyone knowing the. Data Authentication Algorithm (DAA) is a widely used MAC based on DES-CBC. Sorted by: 3. Using compression function the date is hashed by iteration. Templates include all types of block chaining mode, the HMAC mechanism, etc. e. 153 5. The main difference between MAC and HMAC lies in the way they are calculated. Recently, I have been plagued by the differences between a hashes, HMAC's and digital signatures. However, security weaknesses have led to its replacement. This. The algorithm makes use of a k-bit encryption key K and an n-bit constant K 1. UM1924 Rev 8 5/189 UM1924 Contents 7 9. c. HASH-BASED MAC (HMAC) Evolved from weakness in MAC A specific construction of calculating a MAC involving a secret key Uses and handles the key in a simple way Less effected by collision than underlying hash algorithm More secure HMAC is one of the types of MAC. Cipher-based Message Authentication Code, or CMAC, is a block-cipher. 3. Usually, when you encrypt something, you don’t want the. To illustrate, supposed we take the binary keys from the wiki article: K1 = 0101 and K2 = 0111. HMAC uses an unkeyed collision-resistant hash function, such as MD5 or SHA1, to implement a keyed MAC. while AES is intended to allow both encryption and decryption. It should be impractical to find two messages that result in the same digest. difference in values of the. . . bilaljo. It can be used to ensure the authenticity and, as a result, the integrity of binary data. HMACVS HMAC Validation System IUT Implementation Under Test K IThe rfc4493 only provides a test code for AES128. The main difference between MAC and HMAC is that MAC is a tag or a piece of information that helps to authenticate a message, while HMAC is a special type of MAC with a cryptographic hash function and a secret cryptographic key. Name : Aditya Mandaliya Class : TEIT1-B2 Roll No : 46 Assignment No 5 1. HMAC () computes the message authentication code of the data_len bytes at data using the hash function evp_md and the key key which is key_len bytes long. Mã xác thực thông báo mã hóa (Cipher Message Authentication Code - CMAC). Answer The main difference between MAC and HMAC is that MAC is a tag or a piece of information that helps to authenticate a message, while HMAC is a special type of MAC with a cryptographic hash function and a secret cryptographic key. The results of sha1 encryption are different between python and java. Actually, AES-128 is quantum safe; 264 2 64 serial AES evaluations are impractical (and even if it was, CMAC can be used with AES-256). In particular, it is a modified version of CMAC using the insecure DES cipher. The published attacks against MD5 show that it is not prudent to use MD5 when collision resistance is. An HMAC is a kind of MAC. The first two objectives are important to the acceptability of HMAC. In cryptography, a message authentication code ( MAC ), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity -checking a message. 87, while the previous distinguishing attack on HMAC-MD5 reduced to 33 rounds takes 2126. The. For detecting small errors, a CRC is superior. c) Depends on the hash function. Question 7 Alice wants to send a message to Bob. And, HMAC can be used with any Merkle-Damgard hash (which SHA-3 isn't; I suppose you could use any hash, but you'd need to redo the security proof) - perhaps. c Result. Approved by NIST. The hmac. I am trying to choose between these 2 methods for signing JSON Web Tokens. ¶. The receiver computes the MAC on the received message using the same key and HMAC function as were used by the sender,GMAC vs HMAC in message forgery and bandwidth. The first example uses an HMAC, and the second example uses RSA key pairs. HMAC is a key to SSL/TLS security, for the reasons described in this recent email by an engineer at Microsoft. Message Authentication Code (MAC) MAC algorithm is a symmetric key cryptographic technique to provide message authentication. HMAC is a mechanism for message authentication using cryptographic hash functions. See full list on geeksforgeeks. Your other question - why do we need to generate K1 and K2 from K - is a little bit harder to answer, but there's actually a very simple explanation: to eliminate any ambiguity in the message authentication. HMAC (Hash-based Message Authentication Code または keyed-Hash Message Authentication Code) とは、メッセージ認証符号 (MAC; Message Authentication Code) の一つであり、秘密鍵とメッセージ（データ）とハッシュ関数をもとに計算される。. It can be argued that universal hashes sacrifice some. It can be seen as a special case of One-Key CBC MAC1 (OMAC1) which also a MAC function that relies on a block cipher (so AES in the present case). HMAC-SHA256 or HMAC-SHA3-512). Consider first CMAC restricted to messages that consist of a whole number of blocks. 5. Improve this answer. 1: There are collision attacks on MD5 far faster the usual birthday attack. The main difference between CMAC and HMAC is that CMAC is a fixed-length hash while HMAC is a variable-length hash. Message authentication codes are also one-way, but it is required to. However, it follows that only GMAC-8KB is faster than CMAC, and only in the case of longer messages. If your ciphertexts can be long, first concatenating the IV and the ciphertext and then passing the result to HMAC might be needlessly inefficient. . 1. KDF. As very simple KDF function, we can use SHA256: just hash the password. AES-CMAC achieves a security goal similar to that of HMAC [RFC-HMAC]. This compares the computed tag with some given tag. CMAC is a block-cipher mode of operation that is. .