1
vote
0answers
157 views

PGP encryption options

I recently began using PGP desktop and found several options for my encryption capabilities. Which of these (AES, Cast, Triple DES, TwoFish, IDEA) is the most recent, firstly, secondly may the NSA not ...
2
votes
2answers
172 views

Where does the meaning of reduction to a hard problem lie?

Given you a protocol, if we can reduce breaking the protocol to a hard problem, such as DLP or CDH, then we can say that this protocol is secure. Theoretically speaking, reduction is a good method ...
5
votes
1answer
494 views

Where could I submit my algorithm?

I have come up with an encryption algorithm and I am looking for a place to possibly publish it. Any ideas?
0
votes
1answer
173 views

Is AES a linear hash?

So, having read a variety of documentations on AES encryption, I came to the unknowledgeable conclusion that the key schedule applied to the array of chunks, and not just the 14 cycles on a single ...
2
votes
1answer
346 views

What kind of machine can generate 100-400 digits prime number? RSA

The 64 bit machine's biggest number can be 2^63 (9,223,372,036,854,775,807). So what kind of a monstrous machine can generate 100-400 digits prime number? I probably don't understand something, so ...
2
votes
2answers
434 views

Is scrypt a hashing function, encryption, or PBKDF?

I have installed a python implementation of scrypt and noticed it has several functions, both an encrypt and hash function. Yet Wikipedia lists it as being used for PBKDF instead of PBKDF2. Is scrypt ...
3
votes
2answers
217 views

Random session key + predictable IV

I'm using Blowfish in a toy Diffie-Hellman communications scheme. Random session keys are generated for each connection. In this case I can simply feed a null array to the IV right? The same ...
5
votes
1answer
4k views

PBKDF2WithHmacSHA512 Vs. PBKDF2WithHmacSHA1

I'm working on a Java authentication subsystem that specs the storage of passwords in the DB as PBKDF2-generated hashes, and I'm now trying to decide whether I ...
1
vote
2answers
454 views

Reuse of a DH / ECDH public key

I was wondering whether it is safe to use the same DH or ECDH key pair in more than one key agreement, particularly if these public keys are in a public registry. These public keys could be used by ...
2
votes
1answer
1k views

DES Key Schedule Algorithm

Reading through the DES Specification it says that the keys are permuted with PC-1 initially and then shifted left both $C$ and $D$. However, before it gets ...
2
votes
2answers
376 views

Is OTP useful in modern electronic communication?

I have seen from time to time questions about various OTP schemes and "OTP" (i.e. stream cipher) schemes. The most common OTP troubles appear to be: How to extend size of previously generated key or ...
0
votes
1answer
324 views

Key space: Dense and sparse

I'm taking a cryptography class and I come across these terms dense and sparse key space allt he time. What do they mean? As far as I can I understand, dense key space means that there are more ...
1
vote
2answers
4k views

How does GCM (Galois/Counter Mode) work? [closed]

Can somebody explain how this mode works? What view has cipher text and how does it help to authenticate input’s data?
1
vote
1answer
327 views

How is multiplication inverted in IDEA's decryption round?

As we can see in the picture we have a multiplication in this algorithm, we know that two 16 bit inputs should have a 32 bit output, but here we just use 16 bits of the 32 bit output. For ...
2
votes
0answers
334 views

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? [closed]

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? I know you can, of course, use a 4096 bit key for your server certificate, but I usually see 2048 bit ...
5
votes
1answer
7k views

How are the AES S-Boxes calculated?

I'm trying to understand how the AES S-Boxes are calculated. I understand how the multiplicative inverse is calculated over GF(2^8), but I'm confused by the description of the affine transformation. I ...
6
votes
1answer
3k views

How long does it take a quantum computer to brute force AES?

I understand that using Grover's algorithm it only requires $2^{64}$ lookups for a 128 bit AES encryption, leading people to say we need to increase to 256 bit keys. But how long would it actually ...
3
votes
1answer
2k views

How much is slower GCM AES-128 than one of the stream chipher eSTREAM?

Evaluate the speed of the algorithm GCM AES-128 and compare it whith speed of one of the stream chipher in eSTREAM. Can someone give such an assessment?
5
votes
4answers
385 views

Why to try get key out of white box crypto? How can one protect WBC itself?

Help me understand the following. With WBC the question is mainly being stated as can one try to break WBC to identify the key. My question is: Why would one ever want to do that anyways? If one can ...
5
votes
1answer
515 views

Why does NaCl's crypto_secretbox for xsalsa20-poly1305 require the first 32 bytes to be zero?

The NaCl web site says this is a requirement of the API, but its seems more than just an API issue. It means the first 32 bytes of the first salsa20 block are effectively ignored. I didn't see ...
4
votes
2answers
537 views

What is the definition of “security beyond the birthday paradox”?

I'm reading a paper about MACs and I would like to be sure about the meaning of a security beyond the birthday paradox. Is there a definition?
4
votes
2answers
338 views

What (precisely) is a block cipher?

If I follow the wikipedia or crypto.stackexchange definition, any simple XOR encryption where the key is as long as the plain text should qualify as a secure block cipher. Now I thought what would ...
3
votes
2answers
554 views

Encoding information in packet lengths to actively sidestep encryption

If you've only got an encrypted data channel can you actively sidestep the encryption and communicate with an outside party who can see the data but cannot decrypt it? Yes - if you can find some ...
0
votes
1answer
104 views

Quadratic Residues in identification setting

Suppose Alice has two primes $p$ and $q$ such that $p\equiv q \equiv 3 \pmod 4$. $n=p\cdot q$ is part of her certificate to identify her. A party say Bob, sends her a random quadratic residue ${}\bmod ...
1
vote
1answer
116 views

Is there any restriction in using lossless compression algorithms for huge key sizes?

I'm studying McEliece and Multivariate Public Key cryptographic systems. The main problem here is the huge key size. Is there any restriction in using lossless compression algorithms to fix this ...
2
votes
1answer
330 views

Is SHA-256 a one way permutation when restricting the domain to {0,1}^256? [duplicate]

Suppose we consider the space of $\lbrace 0,1 \rbrace^{256}$ as the domain and SHA-256 as our hash function. Does SHA-256 become a one way permutation? Has anyone tried to prove this? Or can it be ...
1
vote
1answer
500 views

Key-size of encryption method

Is there a definied keysize to be used with the "AES_256-CBC" method in PHP, and what is the size? Some background: I want to store encrypted text into a PostgreSQL database. The user who posts the ...
2
votes
1answer
168 views

Repeated Encryption using same/different Encryption systems [duplicate]

I would like to know if there are any security risks/gains from encrypting twice, i.e. $$\text{plaintext}\xrightarrow{encrypt}\text{intermediate text}\xrightarrow{encrypt}\text{ciphertext}.$$ I would ...
4
votes
2answers
3k views

Which stream cipher can we replace the RC4 in the SSL?

In cryptography, the Fluhrer, Mantin and Shamir attack is a particular stream cipher attack, a dedicated form of cryptanalysis for attacking the widely-used stream cipher RC4. The attack allows an ...
1
vote
3answers
270 views

One-Time Pad Distribution of Keys Between Two Parties

Consider the One-Time Pad (OTP). Suppose two parties, A and B, generate a completely random secret key in a real-life meeting, and they keep this secret. Now A wants to send some message to B using ...
2
votes
1answer
370 views

Is using Ed25519 parameters in ECDSA safe?

I recently discovered the Curve25519 key exchange lib and the Ed25519 signature lib. Due to the speculations about NIST-designed curves, there is a chance that I ditch them and use the curves above ...
2
votes
0answers
640 views

How do I enable AES-NI (hardware acceleration) for Node.js crypto on Linux? [closed]

I wrote a basic function to test the speed of the AES-256-CBC mode of the Node.js built-in crypto functions. These functions use OpenSSL, so they should support AES-NI, but when I correctly enable ...
2
votes
2answers
483 views

Do we have to use an IV for AES encryption to be FIPS 140-2 compliant?

I asked this question Will our app be FIPS 140-2 compliant if we use our own AES algorithm implementation here before and although there are some different thoughts about this, the general consensus ...
4
votes
2answers
358 views

Decrypting without using the private key

Let $g$ be a generator of a multiplicative group $G$ of order $q$, $x$ be a private key, and $h=g^x$ be a public key of an exponential ElGamal cryptosystem. Given a ciphertext $c$ produced as the ...
2
votes
1answer
235 views

2 comparable hashes generated from one string

Assume a website where people log in with their password. The password is now stored in sql database as: md5(password + random_salt) We are adding the ...
3
votes
1answer
172 views

Derive a public EC key from two public EC keys

Alice has two EC key pairs: $a_1$, $a_2$ are private keys (integers), $A_1$, $A_2$ are the corresponding public keys (points). Alice and Bob want to create a new public key $C$. Alice must prove that ...
1
vote
1answer
817 views

Hash functions throughput performance [closed]

Without taking into account security, which hash function is the fastest one among the following: MD5, SHA-1, SHA-2 (for various internal size), Keccak, and other… ?
0
votes
2answers
182 views

Blind Signatures

The verification algorithm given in blind signature. Should it work for both Original message and the signature on it Blinded message and the signature on it. If yes, then how can we verify if ...
8
votes
3answers
415 views

Encrypting files with known headers

If I encrypt a file of a known format that has a lengthy header (e.g. an XML Excel file), does that render the encrypted file susceptible to a "known plain text" attack? In other words, if the first ...
-1
votes
1answer
161 views

Use of Different keys with PCBC

Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones ...
7
votes
5answers
805 views

How to prove the security of the PRNG?

Are there any realties tests or criterias that prove the security of the PRNG? What kind of tests or criteria?
1
vote
0answers
143 views

Infinite depth BLAKE2b tree hashing

In the BLAKE2 paper, the authors define Maximal depth (1 byte): an integer in [1, 255] (set to 255 if unlimited, and to 1 only in sequential mode) Node depth (1 byte): an integer in [0, 255] ...
2
votes
1answer
162 views

The Goldreich-Goldwasser-Micali Construction with bad PRGS

I understand that if we have a secure PRG then the Goldreich-Goldwasser-Micali construction gives us a secure PRF. However, what I've not been able to find much material on is how will the GGM ...
2
votes
1answer
203 views

NP complete problems related to permutations of binary vectors or block ciphers

Recently, T.Gowers wrote a blog entry called "How not to prove that P is not equal to NP" about the Razborov/Rudich Natural Proofs paper. He has a construction where he talks about compositions of ...
3
votes
1answer
7k views

Decrypting the password from SHA-512 hash value

I am currently studying AES algorithm and writing a Code using Python. I am trying to add 'Salt' into the user input password, Here is what I am doing, ...
1
vote
0answers
134 views

How many messages needs to be send to server to get AES key in Cache-timing Attack

I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on ...
4
votes
2answers
122 views

post-quantum threshold secret sharing

I am looking for a references for post-quantum threshold secret sharing schemes. I am especially interested in knowing whether any one based on one-way compressor functions or cryptographic hashes ...
2
votes
2answers
338 views

what are the uses of tweaks in block ciphers?

Few block cipher modes has additional parameter , tweaks , especially the ones that are format preserving . Now the comments section of this blog entry says such tweaks can be used for BIN numbers, ...
4
votes
1answer
401 views

AES file encryption with PBKDF2. Safe parameters?

I'm developing an application that will use public key authentication to contact some webservice. So the user has his keypair on his computer, and I want that file to be encrypted using AES with a key ...
1
vote
2answers
220 views

What is the intuition behind AES or SPN?

I'm new to cryptography and have just encountered AES and SPN. I would like to know how the S-box, permutation step and the MixColumn step help improve security. It seems to me (perhaps mistakenly) ...

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