Questions tagged [hmac]
HMAC is a method for constructing a message authentication code based on a cryptographic hash function.
584
questions
1
vote
1
answer
44
views
Can asymmetric encryption be used in HMAC, and still ensure the data has not been tampered with? [closed]
Suppose I want to send a message, but not privately; I want everybody to see it, even an attacker in the middle. I would do this by appending a public key to the start of the data, which could be used ...
- 11
3
votes
2
answers
471
views
Is HMAC part of the TLS/SSL process?
Does HMAC take part in TLS/SSL? When the client and the server pass the TLS handshake and create a common SESSION key, do they also HMAC each message that is being sent out for the purpose of data ...
1
vote
1
answer
116
views
Is it necessary to (length) pad a fixed length one time pad in the presence of a HMAC?
Imagine a protocol where all one time pad messages are of a fixed length. And they're textual only, à la Truths/Tweets. So a short message would be padded with spaces (ASCII 32) up to the protocol's ...
- 13.9k
1
vote
1
answer
161
views
Why does the RFC version of HKDF-Expand start the counter at 1?
In RFC 5869, the definition of HKDF-Expand is given as follows, with the terminating counter value ranging from 1 to (presumably) 255:
...
- 475
1
vote
1
answer
56
views
HMAC data and key swap
In some contexts (HKDF (RFC-5869 sec 2.2) and Bitcoin's BIP32 (master key generation)), I have seen the key and the data swapped for HMAC. E.g., let HMAC be a function $h:\{0,1\}^c \times \{0,1\}^b \...
- 79
0
votes
1
answer
34
views
Storing 4 char prefix for 32bit hex token after storing HMAC digest
Currently I am working on a public api that uses token authentication. The token is a 32 bit random hex that is shared with the user and then stored in our database as an HMAC digest using a secret ...
0
votes
0
answers
60
views
Can a circuit in a zk-SNARK be reversed-engineered?
The definition of zk-SNARK involves not leaking any information from the prover-verifier interaction, but what about leaking information from the circuit itself? e.g., could there be a circuit to ...
- 1
0
votes
0
answers
37
views
0
votes
0
answers
19
views
Has reducing MAC size and increasing message size the same effect on security?
I am evaluating ways to reduce the overhead of (H)MACs on small messages. I was primarily wondering if there is a difference between halving the MAC length or keeping the same MAC length but using it ...
- 101
1
vote
0
answers
106
views
Can a blind "semi-HMAC" scheme using a hash of a blind signature avoid the problems of (provably insecure) blind HMAC schemes?
The impossibility of a secure "blind HMAC" scheme - an HMAC-based analogue of blind signatures - is known (as I understand it, essentially due to the user being unable to validate the ...
- 111
0
votes
1
answer
78
views
CTR HMAC SHA1 vs GCM Key management
The protocol SRTP uses by default AES in CTR mode with HMAC-SHA1.
For my thesis I want to research if GCM would be a better option.
Therefore I read following discussion.
There the answer was that GCM ...
- 15
1
vote
1
answer
67
views
Where should MAC keys come from in a one time pad situation?
I refer to questions For a one-time pad, which MAC method is information-theoretically secure?, Seeking clarification of OTP & MAC discussion and this page illustrating various MACi. And the ...
- 13.9k
0
votes
1
answer
129
views
DIY: password key derivation tool using PBKDF2 / HMAC
First of all, I don't want to reinvent the wheel, just want to build my own car. Non-product environment; only for fun and entertainment.
The goal is to use a single private (and never published) ...
- 1
5
votes
1
answer
216
views
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 ...
- 2,698
3
votes
1
answer
94
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 ...
2
votes
2
answers
151
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?
...
John Smith
0
votes
3
answers
132
views
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 $...
TaihouKai
1
vote
0
answers
163
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
votes
1
answer
70
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 ...
- 123
2
votes
0
answers
43
views
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 ...
- 121
0
votes
1
answer
86
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 ...
1
vote
2
answers
240
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 ...
Studentincyrpto
0
votes
0
answers
16
views
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
votes
1
answer
74
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 ...
- 13.9k
0
votes
0
answers
36
views
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 ...
- 133
0
votes
1
answer
84
views
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 ...
- 91
0
votes
2
answers
185
views
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.
0
votes
0
answers
140
views
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 ...
- 69
1
vote
1
answer
54
views
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 $τ$ ...
- 23
5
votes
1
answer
366
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 ...
- 229
1
vote
1
answer
110
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
votes
1
answer
139
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:...
- 175
0
votes
1
answer
48
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
votes
1
answer
68
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?
- 23
0
votes
1
answer
274
views
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 ...
- 115
0
votes
1
answer
91
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 ?
- 107
0
votes
0
answers
56
views
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 ...
- 107
0
votes
0
answers
24
views
HMAC vs hashing (data + pepper) [duplicate]
Is there a difference between HMAC and hashing (data + pepper) or both of them are equally secure ?
- 107
2
votes
2
answers
119
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
...
- 461
0
votes
1
answer
39
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 ...
1
vote
1
answer
79
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 ...
- 11
2
votes
0
answers
37
views
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 ...
- 408
0
votes
0
answers
48
views
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 ...
- 1
2
votes
1
answer
218
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 ...
- 51
2
votes
1
answer
90
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)):
...
- 41
1
vote
0
answers
99
views
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) ...
- 115
0
votes
1
answer
138
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:
...
- 39
1
vote
2
answers
103
views
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 ...
- 77
2
votes
0
answers
120
views
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 ...
- 43.4k
0
votes
0
answers
469
views
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 ...
- 115