Questions tagged [sha-1]

SHA-1 is a hash function that is two generations old, no longer considered secure for all uses and should only be used for backward compatibility.

Filter by
Sorted by
Tagged with
12
votes
2answers
3k views

How reassuring is 64-bit (in)security?

In Feb 2017, CWI and Google announced SHAttered hash collision attack on SHA1, which took $2^{63.1}$ work estimated 6500 CPU years, to achieve. Therefore, 64-bit should be considered now an insecurity....
32
votes
2answers
41k views

Why is HMAC-SHA1 still considered secure?

This Q & A https://security.stackexchange.com/questions/33123/hotp-with-as-hmac-hashing-algoritme-a-hash-from-the-sha-2-family says that the security of HMAC-SHA1 does not depend on resistance to ...
45
votes
2answers
11k views

Why is SHA-1 considered broken?

Is there a known pair of distinct bit strings (A,B) such that SHA-1(A) == SHA-1(B)? If the answer is no, then how can SHA-1 be considered broken?
98
votes
2answers
18k views

What is the new attack on SHA-1 “SHAttered” and how does it work?

There's a new recent Attack on SHA-1 named "SHAttered" by Google and some researchers. I understand that it uses some fancy new techniques, but not the details. My question is: How? How does the ...
37
votes
3answers
7k views

Does “Shattered” actually show SHA-1-signed certificates are “unsafe”?

Note: I am not advocating anyone continues using SHA1-signed certificates: they are dead as far as security is concerned and should no longer be used. I'm just trying to clarify my understanding of ...
16
votes
1answer
10k views

In 2020, SHA-1 practically broken in chosen-prefix collision (CP-collision). Can double SHA-1 hashing prevent CP-collision?

In a recent study SHA-1 is a Shambles - First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust by Gaëtan Leurent and Thomas Peyrin. 2020, they showed the first practical chosen-...
4
votes
1answer
3k views

How hard is it to generate a simultaneous MD5 and SHA1 collision?

I was recently reading that MD5 is "broken" because it's pretty easy to generate collisions (like 2^(L/2)). And the SHA1 (theoretically) fares no better. The ...
56
votes
2answers
20k views

Is truncating a SHA512 hash to the first 160 bits as secure as using SHA1?

I am from a web development background (I don't know an awful lot about cryptography or how the algorithms themselves work), so I am asking this question in simple terms. Consider a hash of the word '...
30
votes
2answers
44k views

HMAC-SHA1 vs HMAC-SHA256

I have three questions: Would you use HMAC-SHA1 or HMAC-SHA256 for message authentication? How much HMAC-SHA256 is slower than HMAC-SHA1? Are the security improvements of SHA256 (over SHA1) enough to ...
20
votes
2answers
11k views

Why initialize SHA1 with specific buffer?

SHA-1 is initialize with a specific buffer: h0 = 0x67452301 h1 = 0xEFCDAB89 h2 = 0x98BADCFE h3 = 0x10325476 h4 = 0xC3D2E1F0? Why?
8
votes
1answer
6k views

SHA1 no longer considered secure for SSL Certificates — what about Cipher Suites?

Many browsers and Internet companies have recently claimed that SSL Certificates with a signature algorithm of SHA1 will imminently no longer be considered secure. Most notably, Google and Google ...
8
votes
3answers
7k views

Why does Openssh use only SHA1 for signing and verifying of digital signatures?

I am learning SSH protocol. With my current understanding of SSH protocol, I think that message digest algorithms for using in digital signature should be derived from Key Exchange. But Openssh ...
4
votes
1answer
12k views

How is input message for SHA-2 padded?

I read about how is an input message prepared to be hashed by MD4,MD5 or SHA-1: Step1 Append padding bits The input message is "padded" (extended) so that its length (in bits) equals to 448 ...
17
votes
3answers
11k views

After Google's collision attack, is RSA-SHA1 signature still safe?

Google succeeded to get a collision in SHA-1 last year in an attack called shattered. Does this fact make certificates based RSA-SHA1 Signature risky for creating fraud certificates? If RSA-SHA1 ...
11
votes
1answer
2k views

Why are the initial states of hashes functions (like SHA-1) often non-zero?

There is already a question asking "Why initialize SHA1 with specific buffer?" and my question follows on from this: Why are the initial states of hash functions often non-zero? For most, I have ...
9
votes
1answer
2k views

Is HMAC-SHA-1 secure?

Although SHA-1 theoretically has collisions, HMAC-SHA-1 which is based on SHA-1 is still widely used (in TLS for example) and is considered to be secure. How is that possible?
6
votes
2answers
384 views

What is the complexity of finding SHA-1 collisions?

Given the recent news about SHA-1 collisions, what is the complexity of finding a SHA-1 collision? Marc Steven's HashClash is still detailing about 260. Does the previous complexity still hold?
4
votes
2answers
3k views

What does “message schedule” mean in SHA-256?

I am trying to understand the sha-256 algorithm from FIPS 180-2. I understood the padding and parsing of the message string. However after that it states (page 15): For $i = 1$ to $N$: { ...
39
votes
2answers
28k views

Are there any known collisions for the SHA (1 & 2) family of hash functions?

Are there any known collisions for the hash functions SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512? By that, I mean are there known values of $a$ and $b$ where $F(a) = F(b)$ and $a ≠ b$?
12
votes
3answers
11k views

In the SHA hash algorithm, why is the message always padded?

In the SHA hash algorithm the message is always padded, even if initially the correct length without padding; the padding is of the form "1" followed by the necessary number of 0s. Why is it ...
9
votes
2answers
8k views

Is PBKDF2-HMAC-SHA1 really broken?

I just read through this article which demonstrates practical (and seemingly trivial) collisions in PBKDF2-HMAC-SHA1, and provides a few examples of collisions. Am I missing something here? Is PBKDF2-...
9
votes
3answers
3k views

SHA-1 collisions - what about practical attacks?

I understand the theoretical problem with hash collision but when it comes to practice, I get very confused. Suppose a attacker would like to forge a certificate (or any kind of structured piece of ...
7
votes
2answers
3k views

Does a hash function have a Upper bound on input length?

I came across this Answer stating (just a line from the answer):- The input space is "infinite" and thus it has an infinite amount of values that will collide into a single hash And in the ...
7
votes
1answer
748 views

Is SHA-1 still practically secure under specific scenarios?

It is conjectured that SHA-1 has been broken from the "research" perspective but no in real world. That is that there is an algebraic attack that explores weaknesses on its algebraic construction. The ...
7
votes
2answers
568 views

Does a practical collision attack on a cryptographic hash function also mean it fails “indistinguishable from random data”?

It is knowns that SHA-1 has been broken in practice using collision attacks. Related to SHA-1 this mainly had a negative impact on the security of Digital Certificate signatures Email PGP/GPG ...
-3
votes
1answer
162 views
8
votes
2answers
2k views

SHA-1 – Why is it hard to find a certificate collision?

Why is it it’s so much harder to execute a successful collision on certificates than it is on text data? I assume this has to do with the fact the certificate actually is a file that contains signed (...
1
vote
1answer
667 views

SHA1 collision event probability after n iterations

There are String1 and String2 - some variables-strings. The probability of collision for different ...
0
votes
1answer
371 views

Does SHA-1 hash have quasi commutative property? [closed]

Although I have tested with a program and found negative answer, I want to be sure.
17
votes
4answers
63k views

Does the SHA hash function always generate a fixed length hash?

I'm using the SHA1/2 family of algorithms for a particular project. I was wondering if all the SHA algorithms return a fixed length hash regardless of the length of the data.
29
votes
1answer
2k views

How are the functions used in cryptographic hash functions chosen?

I'm learning about cryptographic hash functions and I have some questions about the functions used in the compression function. MD5 uses the following functions: $f_{1}(B,C,D)=(B\wedge C)\lor(D\...
24
votes
1answer
2k views

What is hardened SHA-1, how does it work and how much protection does it offer?

From the shattered website: You can use the online tool above to submit files and have them checked for a cryptanalytic collision attack on SHA-1. The code behind this was developed by Marc Stevens ...
11
votes
3answers
5k views

Accelerating SHA-1

I have a program where computing SHA-1 is the bottleneck. This is using OpenSSL 1.0.0e on a 2.6Ghz 16-core Opteron where I get about 325MiB/s throughput. (SHA1 here is via Andy Polyakov's x86-64 ...
10
votes
2answers
10k views

128 bit hash with least chance of collision?

I'm building a storage system for JSON documents where they are looked up on a 128 bit key. These JSON documents have a timestamp within them, but apart from that are user-entered data. These JSON ...
4
votes
3answers
1k views

Statistical properties of hash functions when calculating modulo

When using SHA-1 to hash an input, the result is a pseudo-random number in the numeric ID space $\{0\dots2^{160}-1\}$. Do I loose any statistical property in the result if I use modulo to restrict the ...
2
votes
1answer
1k views

What's the perfect chain length : number of chains ratio for rainbow tables?

I'm building a SHA-1 rainbow table to crack basic passwords (i.e. up to 10 character, 0-9,a-z), but I can't seem to calculate that golden ratio that would give me the most coverage. What ration of ...
6
votes
3answers
4k views

How to get an output of SHA-1 with first 2-bit are zeros?

Can someone explain what are the ways to get an output of SHA-1 with first 2-bits which are zeros?
6
votes
1answer
22k views

What does AES256-CTS-HMAC-SHA1-96 mean in relation to Kerberos?

I'm not completely clueless as to what it means, but I'd like to understand it at a higher level. The highest encryption type used by Active Directory domain controllers for Kerberos authentication ...
5
votes
2answers
245 views

“One-Wayness” of SHA 1

I recently started learning about Hash Functions for my first time, and I've gone through and have tried to understand the SHA1 process. Brilliant does an excellent job of explaining it step by step. ...
3
votes
1answer
4k views

TLS: Is Integrity assured when using NULL cipher

In specific implementation we're using TLS 1.0, open ssl 0.9.8 but i'm referring to RFC 5246. For performance reasons, I'm being asked if we can use TLS without encryption. The hope is that the ...
3
votes
2answers
253 views

Does “SHAttered” only work for PDF files?

It appears that SHA-1 is broken in practice. The website detailing this attack shows an infographic of how two PDF files can have the same SHA-1 hash value. Also Google's. I've also read Mathew's ...
3
votes
3answers
1k views

For any hash value, is there an infinite number of inputs that hash to it?

Bruce Schneier writes (back in 2005) in a post on cryptanalysis of SHA-1: SHA-1 produces a 160-bit hash. That is, every message hashes down to a 160-bit number. Given that there are an ...
1
vote
1answer
123 views

SHA-1 – Why are text containers used for certificates?

Why are researchers using text files to prove the successful collisions? In the case of the first MD5 collisions I believe it was PostScript-files. In the case of the recent SHA-1 collision it’s PDF ...
1
vote
2answers
129 views

Losing entropy after re-hashing a hash

Suppose you have a string AAA that was hashed with SHA1 to produce 606ec6e9bd8a8ff2ad14e5fade3f264471e82251. If I rehash ...
7
votes
1answer
512 views

Is SHA-1 safe for signing ECDHE parameters?

Is using the SHA-1 algorithm insecure for hashing the ephemeral ECDH public key in the signed_params structure? There are some worrying articles about using SHA-1: ...
6
votes
1answer
6k views

HMAC-SHA1 input size

I know that the HMAC is a message authentication code that uses a cryptographic key in conjunction with a hash function (SHA1 , MD5, etc.). The HMAC output is 160 bits for HMAC-SHA160 and 256 bits for ...
5
votes
2answers
4k views

What does “bits” mean in the context of hash functions?

What does the "bits" in hash functions mean? I started studying hash functions but I still do not understand what the bits mean. What does it mean to say that MD5 is 128-bits or that SHA-1 is 160 ...
4
votes
1answer
341 views

Combining secure hashes with insecure hashes?

Assuming I'm a bank which seeks for secure hash functions to use in the process of signing on digital contents. I'd like to explain / prove why using each one of the following hash functions might ...
4
votes
2answers
525 views

Brute-force attack given small search-space and hash prefix

Suppose we have a value $secret which is a random 56-bit (7-byte) string. Suppose an adversary wishes to discover $secret. The ...
4
votes
1answer
2k views

Can I use SHA1 as license key?

I have recently started looking into creating secure, while not validating against an external server, software product keys. The idea I have had is to create a key consisting of two parts firstly a ...