4
votes
1answer
63 views

Does length-prepending stop length-extension attacks?

Does length-prepending stop length-extension attacks on Merkle-Damgård hash functions, assuming that the length is checked?
1
vote
2answers
123 views

Shamir's ID based signatures - Notation issues

I am currently implementing Shamir's ID Based signature scheme as defined in the original paper (archive link). The sign and verify operation are defined as follows: Sign: $s = g * r^{f(t,m)} (\mod n)...
1
vote
0answers
44 views

Is XSalsa20-Poly1305-SIV a reasonable choice for nonce-misuse-resistant authenticated encryption?

Consider XSalsa20-Poly1305-SIV. This is obtained by: computing a MAC $t_{secret}$ of the plaintext from the key and nonce, as in ChaCha20-Poly1305 except that the plaintext, not the ciphertext, is ...
1
vote
2answers
174 views

PHP AES 256 CBC faster than AES 128 CBC? Or am I doing something wrong?

for last couple of days I'm learning a bit about encrypting data in PHP, as I need a good encryption/decryption function for storing user's passwords in DB. I use ...
3
votes
1answer
116 views

How to correctly encrypt data with proper authentication using AES-256-CBC in php?

I have been using the openssl function for encrypting data with AES-256-CBC in php. I have been able to encrypt it using an unique IV (by generating with openssl_random_pseudo_bytes)for each new ...
3
votes
2answers
369 views

Is authenticated encryption unnecessary if the message is digitally signed?

Normally, it is necessary to use authenticated encryption if the message may be tampered with. Can the authentecation be omitted if the message has been otherwise authenticated?
0
votes
0answers
28 views

NIST SP800-108 KDF modes comparison

According to NIST SP800-108, there are three modes that can build KDF from PRF: counter mode, feedback mode and double-pipeline iteration mode. Assume that the same PRF and input distribution are used,...
0
votes
1answer
56 views

Difference between HMAC-SHA1(key, msg) vs SHA1(key + msg) [duplicate]

Is there any practical difference from using HMAC-SHA1(key, msg) vs SHA1(key + msg) as a way to verify the authenticity/...
3
votes
2answers
70 views

Misuse-resistant authenticated encryption based on SHA-3/Blake2b and AES-CTR/ChaCha20

I am wondering if the following is a useful misuse-resistant authenticated encryption scheme: Parameters (shared by many users): Choose a hash function $H$, such as Blake2 or Keccak. SHA2 could ...
1
vote
1answer
74 views

Is the identity function a one-way function?

The definition of the one way function says: it must be verifiable in polynomial time probability of inverting it less or equal to negligible Now, I am not sure I fully understand one way ...
1
vote
2answers
416 views

What operations are used in symmetric cryptography and why?

In continuation to Why are bitwise rotations used in cryptography?: what other operations are commonly used in symmetric cryptography? Are there particular operations on numbers that are good for ...
5
votes
2answers
117 views

Example of a PRP that is not a strong PRP

The exact definition of security for a pseudorandom permutation is straightforward - for some encryption scheme $E\,\colon\,\mathcal{K}\times\mathcal{D}\rightarrow\mathcal{D}$, it must be the case ...
1
vote
1answer
28 views

Generally accepted algorithm for two-pass, misuse-resistant AEAD that is efficient in software

I would like to know what the standard is for two-pass, nonce-misuse-resistant AEAD that is efficient in software. Thus, AES-SIV is excluded; modes based on a stream cipher like ChaCha20 are ...
2
votes
0answers
189 views

Choosing an optimal generator for an irreducible polynomial over a binary field?

I am reading the Certicom tutorial “An Example of an Elliptic Curve Group over F2m ” and I have following questions: How do they assume that generator $g = (0010)$ is correct for this polynomial? ...
0
votes
1answer
39 views

Considerations on using a single long-term key for file encryption

I'm thinking about designing my own container file format that allows me to store a file in it along with, say, a thumbnail or other metadata. Some of these files are confidential and therefore must ...
1
vote
1answer
34 views

Explanation of protocol secure under random oracle but insecure with any hash fuction

It is known that there is a protocol that is secure in the random oracle model, but where any real hash function makes the protocol insecure. The proof is constructive, but I could not understand the ...
1
vote
0answers
47 views

Effect of the birthday bound on AES-GCM

What is the effect of the birthday bound on the security of AES-GCM, when a very large number of messages are encrypted? I am looking for attacks that are useful in obtaining information about the ...
3
votes
1answer
97 views

Padding in PMAC

How does padding in PMAC work? I have been told two stories: Firstly, I have been told that it works similar to CMAC padding, and secondly, I have been told that it does not need padding. I find the ...
3
votes
0answers
29 views

Can I get an explanation of HDCP's key exchange protocol?

I'm talking about HDCP v1.x. The specification is a too dense for me and easy-to-understand information about it on the net is scarce. What I've gathered is: that there is a master key that is a 40-...
0
votes
1answer
58 views

Proving a function is a one way function

I am trying to prove that a function is a one-way function. The function I am working on in particular is $f'(x,y)=f(x)||f(x \oplus y)$. For what I have understood looking at similar solved ...
0
votes
1answer
53 views

Negative lookup table concept

Interested in password cracking, I thought of a concept for lookup tables that can tell if a hash can be created using a dictionary in about O(log n) time. A simple overview of the idea is a follows: ...
0
votes
0answers
36 views

Encryption of both data and code [duplicate]

Suppose we have 3 parties: Alice possesses invaluable data $x_1, x_2, ...$; Bob can compute some extremely useful function $f$; Carol owns a world's largest data center which have enough resources to ...
11
votes
2answers
1k views

How can I make my cipher show the avalanche effect?

I am a beginner in cryptography. I designed an password based encryption-decryption algorithm, which uses a random salt and a password to encrypt a message. I'm using SHA-512 for hashing, matrix ...
0
votes
1answer
38 views

Key sizes for RSA over elliptic curves

I know that it is possible to define RSA over elliptic curves just as DSA and Diffie-Hellman have been. I know that it doesn't offer much of a speed advantage, but does it at least reduce the size of ...
1
vote
1answer
38 views

Create a potential input for sha-256 hash given a substring of input?

Let's say I'm given a specific SHA-256 hash. Further assume that the SHA-256 input, that yielded this hash contained a known sub-string. Is there a way to find the input (containing the specific ...
4
votes
1answer
61 views

Is there any more asymetric-time permutation than x^3 (mod p)?

I've been using "asymetric-time bijective functions (or permutations)" for several practical uses. I've applied them to solve problems in software-attestation and proof of unique blockchain storage. ...
0
votes
0answers
43 views

Why does Rabin cryptosystem split the message into key blocks?

Why does Rabin cryptosystem split the message into key blocks and not into plain text blocks like in Merkle Damgard Construction? Is it because it acts in a way similar to IV? Probably not, it doesn'...
1
vote
1answer
88 views

Can RSA with padding detect all errors in ciphertext?

I'm new in cryptography and there are a couple of things that i'm not sure if i understand correctly. First, when using padding (PKCS or OAEP), if the chiphertext has errors in transmission we'll we ...
1
vote
1answer
58 views

Why does a hacker need to crack the key to an encrypted file, instead of just brute forcing the password? [closed]

Most encryption softwares don't seem to have a trial limit. So why would a hacker need to crack the key, or even need to know the salt value, if he can just brute force the 6-8 digit password?
5
votes
1answer
42 views

Terminology for secret sharing

To my understanding, there are two "approaches" to t out of n threshold encryption. In both of them, n shares are given to different shareholders, and at least t of them must agree to "proceed". "...
2
votes
1answer
68 views

Can gnupg master key decrypt something encrypted with subkey?

When creating gpg subkeys, the master key signs and certifies that a subkey belongs to that master. That's ok, but, can master key decrypt something encrypted by a subkey? I guess no, but I want to be ...
0
votes
0answers
25 views

gnupg master key with certificate and authentication capabilities

After researching about GPG and Smartcards I came to a dilemma. The usual setup I've seen more widely is a master key (with SC capabilities) and 3 subkeys (with S, E, A each): ...
1
vote
1answer
66 views

How to calculate secret key size of a CP-ABE scheme

How can I calculate the real size of key in a CP-ABE scheme. For example, I have this GSWV scheme: Fuchun Guo, Willy Susilo, Duncan Wong, Vijay Varadharajan: CP-ABE with constant-size keys for ...
3
votes
2answers
121 views

Can RSA (theoretically) be used as a block cipher?

Assume AES gets a devastating attack making it unusable. Is it possible to use RSA in a secure way that can encrypt data in bulk? I can't see how RSA (assuming OAEP padding) can be used in normal ...
0
votes
1answer
19 views

What will browser show when a user access website and website present certificate of some other domain with same top level domain [closed]

For example, User tries to access a.example.com and server presents abc.example.com with a.example.com not in SANs list. Will it be just a warning or an error?
0
votes
1answer
50 views

Usage of 3DES for single block

I have a device, HASP, which has functionality to encrypt 8 byte data using 3DES in ECB mode, with three different keys, I am interested how secure is this? I know it might not be most secure, but how ...
3
votes
1answer
272 views

Is it possible to perform a rudimentary asymmetric key encryption algorithm by hand?

I have at least three, distinct motivations for having a simple way to use asymmetric key encryption by hand or without modern computers. First, I was recently demonstrating to a 12-year-old how ...
1
vote
1answer
41 views

Attacks on MICKEY 2.0 Stream Cipher

I would like to know if there are any known attacks, besides from side-channel attacks (differential fault attack, correlation power analysis, template attack), against MICKEY 2.0 or MICKEY-128 2.0. ...
2
votes
2answers
367 views

Many consecutive hashes to slow down brute force attack?

I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to brute force, without a ...
5
votes
1answer
142 views

Diffie-Hellman when $p$ and $g$ are pre-agreed and hidden from Eve

During a regular Diffie–Hellman public key exchange, Alice and Bob agree to use a prime number $p$ and a base $g$… which are both made public and are therefore also assumed to be known by Eve. Alice ...
4
votes
3answers
103 views

Choosing which is public vs private key

When I calculate two RSA keys, what if anything, would make any difference which I call the public vs which I call the private key?
1
vote
1answer
247 views

How can a lattice attack be applied to ECDSA signatures?

The aim is to check if it is possible to break the ECDSA cryptosystem under the following criteria. Suppose that each ECDSA signature is generated by using the GLV method for point multiplication (...
3
votes
2answers
241 views

Why are recomended RSA key lengths so high? [duplicate]

I was checking for authoritative sources to back up my recommendation of a minimum RSA key length of 1024 and was shocked to find that NIST 800-56Br1 and FIPS 186-4 both recommend at least 2048 bits ...
5
votes
1answer
91 views

Do Carter–Wegman MACs allow key reuse if the MAC tag is kept secret?

Poly1305 (and GHASH) are secure authenticators, but only for one use. Thus, nonce reuse in Poly1305-AES, ChaCha20-Poly1305, and AES-GCM all reveal the authentication key. However, my understanding ...
10
votes
2answers
931 views

How does hash speed vary based on string length?

Surprisingly I have not been able to find an answer to this question on Google. If I have a function that is based on any of the popular hashing algorithms used for password generation, by what ...
2
votes
2answers
86 views

Semantic Security and Equal Message Length in the Context of Public Key Cryptography

A lot of definitions for semantic security make use an experiment $\text{Exp}$ which is performed between a challenger $\mathcal{C}$ and an adversary $\mathcal{A}$ that begins as follows: $\mathcal{C}...
0
votes
1answer
80 views

Is it ok to store the plaintext hash of encrypted data

Is it ok to create and store the hash (unkeyed hash function) of a plaintext before encryption or does it lead to vulnerabilities? If it is ok are there requirements for the used hash function and ...
1
vote
1answer
24 views

How is the usual way of using PKCS5/7 when a weird data is given?

PKCS5/7 pads the remaining data elements with a binary representation of how many space requires padding. This is useful and compact but what should I do in the following sample scenario below ? ...
2
votes
4answers
185 views

Are there transitive ciphers (either symmetric and asymmetric)

Say Alice has information that's already encrypted with Bob's key. She wants Bob to decrypt it without knowing what he just decrypted. So she encrypts it with her key and sends it to him, he decrypts ...
1
vote
0answers
44 views

Can anyone tell whether this RHO step of SHA3 is correct?

In rho step of SHA3, I have done right circular rotation whether its correct ?? I am doing in Verilog so I am using concatenation operator for rotation. For x=0 and y=1 that is A[0][1] rotation will ...

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