Questions tagged [hmac]
HMAC is a method for constructing a message authentication code based on a cryptographic hash function.
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HKDF randomness extraction - salt or no salt?
According to the HKDF paper, the use of a salt serves two purposes: domain separation and randomness extraction.
This question is solely about the necessity of a salt for the purposes of randomness ...
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1answer
57 views
Applications in which you should/shouldn't use a salt with HKDF
rfc5869 has the following to say about the use or lack thereof of salts with HKDF:
HKDF is defined to operate with and without random salt. This is done to accommodate applications where a salt value ...
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Message Authentication Code (MAC) calculation using OpenSSL
I have (1) a cipher text (2) a key and (3) an IV. I need to find the authentication tag of the cipher text. It is known that the authentication tag is created with the HMAC-SHA256 message ...
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Benefits of HMAC-based server authentication [migrated]
Context and assumptions:
TLS 1.2 or 1.3, server authentication only
Client uses HMAC to authenticate itself to the server, using a PSK key
Client is a library, not a web browser, which doesn't allow ...
2
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2answers
52 views
Why bother to generate Key, IV and encrypt them?
When we perform encryption with Public or Private Key, Asymmetric AES with RSA and CBC 128, and when we use the padding as well. Why do we have to bother adding the additional:
Key + IV?
...
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3answers
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Zero-knowledge proof of HMAC digest
I'm reading the Wikipedia for HMAC, and I feel a little bit lost.
I'm wondering if there exists...
$$digest = \operatorname{HMAC}(msg, key)$$
Is it possible to prove that $digest$ is computed from $...
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0answers
67 views
Why does HMAC use the hash twice? [duplicate]
According to the HMAC specification in RFC2104, an HMAC is computed in the following way:
HMAC(K, text) = H(K XOR opad, H(K XOR ipad, text))
where ...
2
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1answer
60 views
Should I use HMAC to create a multiple part HASH token
I have a web API with a custom API authentication system that users each have a SecretKey and a public ApiKey. Using these two keys client(or user) can generate a token for the authentication on the ...
2
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0answers
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key reuse: does knowing H(S) reveal HMAC(S)
given a hash H() , like sha256
and a secret text S
and a public salt P
will knowing H(S) reveal HMAC(P, S) ?
to clarify: the question is if it possible to learn the digest, not the secret.
In my ...
0
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1answer
67 views
Reverse SHA256 Hashed Value from Multiple Instances where Part of Hashed Value is known
I apologize in advance if this question has been answered already. However, I have not been able to find an existing answer - despite the case being pretty simple and common I imagine. Perhaps there ...
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1answer
157 views
Why is birthday attack invalid on this MAC
I am trying to understand why the following birthday attack is invalid for this MAC construction.
Let Mac : $\{0, 1\}^{128} \times \{0, 1\}^{256} \to \{0, 1\}^{128}$ be a MAC. Consider the following ...
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Use HMAC for every block encryption operation [duplicate]
Is it possible to use HMAC while performing encryption of blocks?
I think that the main problem with the approach would be to get the same output size as the block, from the HMAC function.
Also, the ...
0
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1answer
66 views
Can a one time public key'd HMAC be secure?
Imagine authentication like $hmac = H(nonce, ciphertext)$. $nonce$ is truly random and chosen (randomly and WITHOUT replacement) from predetermined set $N$. So ${nonce} \in N$ and once used cannot be ...
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What is the difference between HMAC-SHA3-512 and KMAC? [duplicate]
Reading through the wikipedia entry for HMAC I see that SHA-3 can be used with the HMAC algorithm to give HMAC-SHA3-512.
I also know that there is KMAC, which from ...
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1answer
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How to produce Auth Data and tag in GCM? Does MAC appended CTR mode encrypted text weaker than GCM?
In https://en.wikipedia.org/wiki/Galois/Counter_Mode, there's a diagram which tells us how GCM works in general.
I have watched computerphile video on how ECB,CBC and CTR mode works and able to ...
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1answer
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is there any good attack model of HMAC?
are there any good attack models of HMAC ? like how it can be attacked ? if there are any possible attacks of HMAC i would be happy to know about it.
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What is the need of xor-ing the key with an outer and inner pad in HMAC?
The diagram above shows the standard HMAC algorithm. However
consider the algorithm of HMAC without xoring the key with outer or inner pad. In other words let the structure of HMAC remain the same ...
1
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1answer
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Is the collision chance 2^(n/2) of an n-bit tag τ unchanged if reduced to (n/2)-bits using a reduction of τ to some 2^(n/2) order group element?
If $H(k, Μ) = τ$, in the context where $τ$ is an $n$-bit tag produced as a mac on a key, $k$, and a message, $M$, through a keyed-hash function, $H$, is there a function $F(τ) = T$ that transforms $τ$ ...
4
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1answer
318 views
Does hashing an ECB encryption with a strong hash function produce a secure MAC?
Does applying a strong hash function like SHA-256 to the ECB-encryption of a message (using some secret key $K$) produce a secure mac? For example, given a message $m$, would a simple mac construction ...
1
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1answer
69 views
HMAC key generation and encoding
I've this piece of .NET code that is based on a Microsoft sample on how to generate a key and sign using HMACSH256.
But I've altered the key generation a little bit and also decided to use Base64 to ...
0
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1answer
74 views
What authenticated encryption do kerberos use in windows?
I have learned about the kerberos protocol and seen that the windows version uses a couple of authenticated encryption schemas (like rc4-hmac-md5).
What type of authenticated encryption is it? Is it a:...
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1answer
45 views
Necessity of PBKDF2 in current Setup?
I have a single password which is random bytes that encrypts a database. Right now I am using an encryption scheme of https://gist.github.com/jbtule/4336842. To summarize, we take our one password, ...
2
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1answer
65 views
Can future time-based keys be deduced from a previous key?
If a time-based key generated by an authenticator app like Google Authenticator is compromised, can future keys be deduced from the compromised key?
0
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1answer
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Does SHA384 make sense with HMAC-SHA256?
In the sense of security level (as defined, for example, by Ferguson and Schneier in the book Practical Cryptography), does it make sense to use SHA384 with HMAC-SHA256 in the general settings. By ...
0
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1answer
51 views
Use peppers with Bcrypt (HMAC + Bcrypt)
Is it useful to combine HMAC with Bcrypt ?
If it so, should I do the HMAC on the password before "Bcrypt"ing it ? or should I do the HMAC on the Bcrypt output ?
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Managing master keys used in PBKDF2 and HMAC (store, rotate)
My use case:
I have few master keys, I use each for a specific operation (e.g. one for encrypting user's data and another for creating JWT signatures etc...).
I use these master keys in two specific ...
0
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0answers
20 views
HMAC vs hashing (data + pepper) [duplicate]
Is there a difference between HMAC and hashing (data + pepper) or both of them are equally secure ?
2
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2answers
90 views
AWS signature v4 key derivation
Generating Authorization header with AWS signature v4 involves deriving signing key as follows:
https://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html
...
0
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1answer
35 views
Complexity of deriving message from CMAC vs HMAC when the key is known
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.
After obtaining the key and tag for CMAC, an intruder can apply ...
0
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1answer
67 views
How to compose multiple values to MAC authenticate?
If the data I want to authenticate consists of multiple values and I compute a MAC simply concatenating the values, an adversary can "shift" characters within those values without ...
2
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0answers
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Confused about encapsulation using different types of hash functions
I'm reading Improved Efficiency for CCA-Secure Cryptosystems Built Using Identity-Based Encryption. In Section 4 there is a description of encapsulation schemes that says
We suggest an encapsulation ...
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Is 64-bit SHA-256 IV-based MAC for fixed-length messages reasonably secure?
I want to use truncate8(SHA256-nopad(IV=secret, message)) as a 64-bit MAC, where message is guaranteed to be exactly one hash ...
2
votes
1answer
143 views
What does the running transcript hash in RFC-8446: TLS 1.3 do?
From RFC8446:
In general, implementations can implement the transcript by keeping a
running transcript hash value based on the negotiated hash. Note,
however, that subsequent post-handshake ...
2
votes
1answer
77 views
Question about IETF RFC6979 determinisitc (EC)DSA document section 3.6 additional data k'
In RFC6979, on page 14, Section 3.6 "Variants":
o. Additional data may be added to the input of HMAC, concatenated
after bits2octets(H(m)):
...
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0answers
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What's the difference between H(m) $\oplus$ H(key) and H(m || key) in MAC construction?
We all know that HMAC has the form of $H(ikey || H(okey || M))$. I'm wondering what if we replace the H(okey || M) into H(okey) $\oplus$ H(M)? In other words, is $$H\Big( ikey \mathbin\| \big( H(okey) ...
0
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1answer
97 views
How to calculate a hmac and cmac
I'm searching for a simple description that tells me in a schematic way how hmac and cmac is calculated.
So far I found the following:
...
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0answers
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Why doesn't appending a message to a key instead of vice versa defeat length extension attack? [duplicate]
It's well established that H(K||M) is vulnerable to length extension attacks for SHA-2 and other hashing algorithms, and instead an HMAC construction should be used. However - why can't H(M||K) be ...
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2answers
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Is nonce-less Encrypt-then-HMAC as secure as poly1305
While reading https://crypto.stackexchange.com/a/88732/87450 I noticed that it suggests encrypt-then-HMAC as a defense for partition attacks. However as far as I know unlike poly1305, HMAC does not ...
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0answers
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Encrypt-then-HMAC with a single key is secure?
The partition oracle attacks exploits the non-committing AEAD schemes.
Informally, a committing encryption scheme is one for which it is computationally intractable to find a pair of keys and a ...
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0answers
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Bitcoin Key Recovery Without Nonce Re-Use
There are a lot of questions in these forums regarding the recovery of private keys.
But I'm here to postulate on something unique to a specific piece of research that I looked into recently.
The ...
2
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1answer
412 views
Generating HMAC(SHA256) keys using WebCrypto deriveKey() API
I am using the javascript WebCrypto API window.crypto.subtle.deriveKey() API to generate HMAC keys like this:
...
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0answers
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Is Poly1305 enough for cascading ciphers? [duplicate]
ChaCha20 along with Poly1305 provides confidentiality and integrity. Now suppose I cascade AES on top of ChaCha20. Is it safe to assume that the Poly1305 MAC is still secure, even if I cascade ...
0
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1answer
78 views
How do high hash rates affect hashed password security?
Given the increase in hash rate since the rise of numerous block chains, I wonder how this affects the security of many hashed password systems.
Is a standard linux ...
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0answers
45 views
Authentication tag length and post-quantum security
The recommended hash length for post-quantum security seems to be either 384-bits or 512-bits. 512-bits gives 256-bit collision resistance, and 256-bit security is obviously ideal for post-quantum ...
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Randomizing output of HKDF for the same input key material [duplicate]
Given HKDF and a master input material key $k$, I would like to derive ephemeral keys that cannot be linked together. If I understand correctly, the specification of $HKDF$ adding a unique random $...
1
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1answer
161 views
HKDF Bit Security
I've always understood the bit security of hash functions to be related to their output size (eg. collision resistance). However, I recently came across a table from a Wickr blog post that lists HKDF-...
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Forgery of the Carter-Wegman MAC
Consider the nonce-based Carter-Wegman MAC which works on key space $K=\{0,1\}^n \times \{0,1\}^n,$ message space $M=\{0,1\}^{mn}$, nonce space $N=\{0,1\}^n$ and the tag space $T=\{0,1\}^n$ as follows:...
4
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1answer
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Is HMAC-SHA256 a PRF?
In the abstract of The Exact PRF-Security of NMAC and HMAC, Gazi, Pietrzak, and Rybar state:
NMAC was introduced by Bellare, Canetti and Krawczyk [Crypto’96], who proved it to be a secure
...
4
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1answer
159 views
Is the HMAC of a broken hash such as MD2, MD5, SHA1 etc, also broken?
As we know, MD5 and SHA1 (to some extent) are broken, and older algorithms like SHA0 or MD4 and MD2 are very broken.
Does this also imply that the corresponding HMACs are also broken?
Obviously nobody ...
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How secure is Encrypt-And-MAC?
From this popular Crypto.SE thread, the general feeling is that Encrypt-Then-MAC is the most secure. From the first answer, the poster says that Encrypt-And-MAC provides integrity of the plaintext. If ...