Questions tagged [hmac]
HMAC is a method for constructing a message authentication code based on a cryptographic hash function.
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Create a TOTP for machines using HMAC or AES
I'm trying to create a sort of Time-based One Time Password (TOTP) where machines are involved (not humans). In this kind of TOTP the step is 15 minutes between one code to the next one and both ...
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Is an HMAC based on a second-preimage resistant hash function always unforgeable?
If hash function is collision-resistant, then its associated HMAC is always unforgeable. But suppose that a hash function is only second-preimage resistant, not necessarily collision-resistant. Then ...
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Does HMAC support or guarantee confidentiality? [closed]
I know that HMAC supports or guarantees both authentication and integrity, but does it also provide confidentiality?
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Break HMAC-SHA256 of PAN with known hash?
Imagine a database containing hashed (HMAC) Primary Account Numbers (PANs ) and associated identifiable information (e.g. transactions).
Consider a data breach. Prior to the breach, an attacker made ...
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1answer
73 views
Is it acceptable to use a HMAC-SHA256 hash as a secp256k1 private key?
Say I want to generate a deterministic private key related to some data, for instance to a domain name. The easiest way I can think of is:
take a secret material which will work as "generator&...
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1answer
50 views
Authenticated, Quantum-resistant GPG2?
GPG2 does not provide authentication. It still uses SHA-1 by default. It does not seem to get any stronger as time goes by.
If one were to pass a randomly-generated symmetric key (from a TRNG) over ...
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1answer
42 views
Is it safe to use the same password/secret for both VeraCrypt volume and its HMAC?
I am trying to script the integrity check of a VeraCrypt volume.
...
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2answers
100 views
Extending AES-GCM initialization vector
We all know that applications of crypto primitives like to not think about the management of nonces, and initialization vectors and often prefer to just set them to random values. This sometimes leads ...
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1answer
568 views
How is it possible that these two encryption functions yield the same result?
I opened this post in stackoverflow some time ago where I explained a problem I had about not finding a way that would allow to successfully get the result of a string encrypted with a "aes-256-...
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1answer
35 views
HMAC SHA256 - fixed vs dynamic key - security and collision impacts
Assume we should apply an hmac sha256 on different messages made of incremental numbers (Ex. 1 to 1 billion).
Does it make sense in terms of security to apply a different fixed key for each message?
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1answer
87 views
With AES encryption and a known key and plaintext, can an attacker create a different key and plaintext resulting in the same ciphertext?
In short: with AES encryption can an attacker create a new key2 and plaintext2 so that AESkey1(plaintext1) = AESkey2(plaintext2)
If so, can it be solved by just applying for instance a MAC like AES-...
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1answer
45 views
HMAC for hash list
If I have a very large input to hash with a hash function vulnerable to length extention and I am using a hash list, should I HMAC each part of the input or just HMAC the final hash of all the hashes ?...
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Using HMAC with AES modes that do NOT require padding [closed]
I'm trying to use HMAC with AES modes that do not require any sort of padding.
Although I am aware that modes like AES-GCM and ...
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1answer
58 views
OpenSSL FIPS integrity check
As far as I know, FIPS requires a set of self tests (POST) to verify the cryptographic algorithms permitted and the integrity of the module.
These tests are performed at run-time, so OpenSSL does a ...
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1answer
60 views
What is the best way of deterministically choosing N of M, given 32 bytes of sha256?
I have a list of M=10,000..100,000 items and 32 bytes of sha256 H.
I want to choose N=10..100 items (without order).
Is there an efficient way to do this?
Or should I use something like ...
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0answers
41 views
Why the salt is used as a key in the extract phase of HKDF?
What is the reason that in the HKDF standard (RFC5869), in the "extract" phase, the 'salt" parameter is instantiated as HMAC key, and the secret keying material 'IKM' is instantiated as HMAC input ...
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1answer
50 views
Is it okay to reuse a single symmetric key for a large volume of messages and HMACs, so long as “nonces” are randomly generated for both of them?
https://www.reddit.com/r/crypto/comments/fnku50/nonce_reuse_vs_iv_reuse/
Nonce reuse with the same key is catastrophic to security. The same premise holds for
initialization vectors. If the key ...
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0answers
24 views
Integrity for mixture of encrypted/unencrypted database fields
I have multiple blobs each (symmetrically) encrypted with its own randomly generated key.
Now I want to encrypt these blob keys with user keys and store them in a database.
A table could have the ...
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1answer
82 views
Why Authenticated Encryption the same message again is not secure?
It is the Exercise 9.14 (9.1) from the book A graduate course in applied cryptography by Boneh and Shoup.
Let $(E, D)$ be an AE-secure cipher.
a. $E_1(k,m):=(E(k,m), E(k,m));$
$$D_1(k,(c_1,c_2)):= ...
0
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1answer
47 views
does using an HMAC protect against hash table DoS attacks?
For a hash set where the values are supplied by a third party, one concern is that an attacker can run a denial of service attack by creating many values that all fall into one bucket of the hash ...
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2answers
121 views
What is the difference between a PRF and a PRP, and are cryptographic hash functions the same as HMAC (PRFs or PRPS)?
I read one answer to a similar question that put forth that a hash function is distinct from a PRF, however I've also found materials purporting that cryptographic hash functions are PRFs, and I'm not ...
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1answer
66 views
Is it possible to affect the output of HMAC w/ SHA-512 by providing it with a custom message?
Consider an HMAC algorithm that uses SHA-512 with an unknown private key. Is it possible to affect its output, either partially or totally, by providing it with carefully crafted messages?
For the ...
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0answers
65 views
Why is double encryption used to generate EphIDs in DP3T?
The most famous proposed COVID-19 application is DP3T. In this app a user constantly broadcasts EphIDs generated from a secret key as follows:
$$EphID 1 || ... || EphID n = PRG( PRF(SK_t , “broadcast ...
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0answers
36 views
How to generate temporary Credentials for TURN server Using TURN REST API in Java
I am new to this site, hence I apologize for my English and way of phrasing the question. I am trying to generate temporary credentials to my TURN server using the TURN secret that I generated with ...
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1answer
101 views
Does pepper *require* an HMAC?
Assume you are already given a properly-salted, password hash $X$ from some slow PBKDF (e.g., like Argon2id).
Now, you want to apply some large (~256-bit) secret "pepper" $S$ to it before storing it ...
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1answer
34 views
how to predict a sequence for reverse engineering of a ticketing system [closed]
i am student in the fith year of college IT-science and a crypto noob.
i have been wondering how the folwing sequence of ticket i bougth in all at once were built for :
how they work or how they are ...
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0answers
171 views
How to bruteforce password from HMAC-SHA256 hash (if you have the key)?
Short of creating one's own script / program, is there an existing, readily available way of iterating through a list of potential passwords to find which one corresponds to a hash (HMAC-SHA256), ...
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1answer
65 views
Key at start or end of HMAC
In the book Information Security Principles and Practice, the author explains why HMAC should be used for integrity with a symmetric key with the message, to prevent a MiTM to replace both the message ...
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1answer
167 views
SHA1 standard steps
I'm a computer engineering student and I want to implement a cryptographic function for a college project. I want to realize my personal implementation of a WPA2 hash producer in C (and upload it to ...
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2answers
126 views
Can a MAC be used as a HMAC?
I am reading through an information security book right now, and a confusing question poses itself to me:
"Could you use a MAC as a HMAC? That is, does a MAC satisfy the same properties that a ...
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1answer
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How many codes can I safely generate using the same HMAC key?
Can an attacker guess the key given enough codes for the same key? And if so, how many times is it safe to use the same key?
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2answers
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How to design a secure challange-response authentication protocol?
I am implementing a custom challenge-response protocol to authenticate a client to a server. Mutual authentication is not required, i.e. the server doesn't need to be authenticated to the client.
The ...
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1answer
53 views
Using the output of HKDF directly
I am using HKDF with an IKM and salt, the OKM is used as the key for an HMAC operation. The HMAC algorithm is authenticating messages in a communications system
The salt is the concatenation of 2 ...
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1answer
119 views
Length extension attacks, Merkle–Damgård constructions, and HMACs
The wikipedia page for Length Extension Attacks says "Note that since HMAC doesn't use [Merkle–Damgård constructions], HMAC hashes are not prone to length extension attacks."
However, HMACs can be ...
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1answer
45 views
How to implement nonce for hashing a 6 digit sensitive number with hmac with its secret key
I have to pass a 6 digit number which has to be kept very secret through a unsecured netwok.
I am thinking to hash it using hmac and a secret key which only me and the reciever knows
So the code ...
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1answer
52 views
can I use PBKDF2 instead of hmac as a hashing tool for sensitive data
I have read about hmac and PBKDF2.
PBKDF2 - is mainly used for password hashing. It uses ...
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1answer
89 views
Security Considerations in using SHA-1 for One Time Passwords
SHA-1 is considered broken. That's why I'm assuming that using SHA-1 for RFC2289 OTPs is broken as well. Is this assumption correct?
Going further with this assumption using SHA-1 for RFC4226 HOTPs ...
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2answers
60 views
Can the HMAC of a pre-hash be considered equivalent to an HMAC of the message?
Assume:
size of m = 1kB
HMAC hashing function = SHA256
H hashing function = SHA256
It seems reasonable to think that there would be no difference in authenticating a message if either HMAC(k, m) or ...
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1answer
132 views
The output size is smaller than input size is a insecure to hash function [closed]
Why it will be unsafe, and can be break?
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What's the use of HMAC in PBKDF2? [duplicate]
As far as I know, PBKDF2 uses an underlying pseudorandom function in order to generate a hash (like SHA256) so as far I understood PBKDF2 is basically a hash function that uses an underlying function ...
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1answer
141 views
Protect the original message of a hash from brute force
My apologies for the somewhat inaccurate terminology.
Basically I have some simple messages (entropy ~50 bits) the user will use for registration. The messages should remain private, and I don't ...
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1answer
105 views
HMAC of message hash
If I have a message m and want its HMAC, I can simply do HMAC(k, m). But sometimes I am not given ...
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1answer
89 views
An unusual use-case for HMAC as compression function in web browsers
It's an unfortunate fact that, right now (2019), browsers don't expose standardized streaming hashing interfaces in SubtleCrypto. The only way to hash a file, is to ...
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1answer
110 views
Is it OK to just hash a symmetric key to derive an authentication key?
I'm using xsalsa20poly1305 for encryption in my program from libsodium. The recommended size for chunks is 4 kB. In that case, poly1305 will have authentication only for the the individual 4k chunks. ...
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1answer
51 views
Termonology help: What is using AEAD without encrypting data called?
I'm using ChaCha20-Poly1305 in a "full AEAD" mode, where a payload of data is encrypted and a block of unencrypted "additional data" is secured as well.
However, I'd like to also occasionally use the ...
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2answers
146 views
Does HMAC provide anything that AEAD does not?
Alice and Bob have to talk through Eve. (server to device through untrusted third party that relays messages, no TLS available)
Assume a secure key. Out of scope. Example, ECDH key exchange with HKDF....
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Some curiosity about HMAC
Is the probability of distinguishing HMAC from a random oracle is the same as the probability of forging HMAC?
Can we say that the following statement is trivial?
$\Pr[\text{Forging $\operatorname{...
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1answer
139 views
are there more efficient methods than HMAC to achieve convergent encryption?
I’m thinking about the convergent encryption system described in the top answer to this question. However, it seems like preferred modern HMAC algorithms like HMAC-SHA256 (as used in step 2 to create ...
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0answers
46 views
Probability of collision of two HMACs with two random keys
Assume $k_1$ and $k_2$ are two $\lambda$ bit random number ($|k_1|=|k_2|=\lambda$), and HMAC generates $f(\lambda)$ bit tag. How much is the probability of their collision for an input message $m$?
$...
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1answer
94 views
Is this function a secure MAC?
Consider the following function:
$f_k(mm')=\operatorname{HMAC}_{\operatorname{HMAC}_k(m)}(mm')$
Can I use $f$ as a secure MAC?
