Cryptography is the practice and study of logical means used to achieve information confidentiality, integrity and authenticity. It covers, among other things, encryption (making some data unreadable except for those who know a given secret element, called a key), data hashing (in particular for ...

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Which strategy to encrypt data accessed by multiple users?

I need suggestions to design my database architecture (in the context of a web application) on the particular point of its encryption ; knowing that the following elements must be respected: 1- Data ...
7
votes
3answers
1k views

Why do we have such big keys?

In Chapter 7 of Applied Cryptography, Bruce Schneier claims that, due to thermodynamic limitations, "brute-force attacks against 256-bit [symmetric] keys will be infeasible until computers are built ...
5
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4answers
1k views

Client side encryption - only web browser available

I am creating an enterprise application, the server side runs a whole set of different apps, On the client side, there is only a webpage, no applet or anything else. Unfortunately data created by the ...
2
votes
2answers
2k views

Understanding salted password hashing using Java

Context: I am using this tutorial and trying to understand and implement salted password hashing using Java. After spending some time on this topic, I figured out that the basic idea is to: Convert ...
0
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2answers
57 views

Is there a way to give out secure tickets wihout storing them?

I'm building a website on which I want to make it very easy for users to create pages anonymously and later be able to come back and edit those pages. One way to do so is to give out confidential ...
0
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1answer
82 views

How to authenticate users?

I'm in the scenario that I'm planning a detailed description on "how to securely encrypt files" without putting too much in one Q/A. So, in a file-encryption scenario, what are the possible ways to ...
1
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1answer
49 views

Is the method of hardening the creation of a Cryptographically Generated Address (CGA) called hash extension

CGAs are sha1 hashes truncated to a 59 bit value. Along with a 3 bit security parameter they form a IPv6 address (more precisely the interface identifier). from wikipedia: The Sec parameter ...
4
votes
1answer
121 views

One time password question

Suppose F(X) = (5X) mod 9 is used to generate a one time password. I am supposed to generate the first 8 values using the above formula, starting with the seed value of F(5) Well I know that F(5) = ...
2
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3answers
256 views

How can two parties compare whether a simple (5 letter) shared word matches, without disclosing their word to each other?

I'm having some trouble with this scenario, some advice would be great. The context is that a group of people have each been give a simple 5 letter word - for example: Alice: ACTOR Bob: JEANS Dan: ...
4
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2answers
323 views

Sharing RSA keys between PGP and SSH protocols: Does this pose a security risk?

If I generate a PGP subkey that only has the authentication capablity and use this to generate an SSH keypair to authenticate Git for example, does this pose a security threat? When I do, should I ...
1
vote
1answer
165 views

Can DUKPT BDK be 192 bits?

All examples seem to be with 128 bits. Can it be 192 bits?
0
votes
2answers
99 views

Is there a cryptographic function that generates a reconizable visual pattern?

I have to build a system that will ultimately print a pass allowing access to a building. The validation of this ticket will be done manually (it can also be automatic but that's not likely at this ...
0
votes
2answers
201 views

How is encryption broken [duplicate]

The title describes pretty well what I want to ask, because I just can't wrap my head around it. I understand the basics of breaking encrypted data with the method of kind-of-bruteforcing where you ...
5
votes
1answer
333 views

How secure is CertiVox M-PIN?

CertiVox have designed a system with the aim of "getting rid of passwords". Essentially the system authenticates users with two factors of authentication: A 4 digit PIN and a token stored within the ...
0
votes
1answer
438 views

Google Chrome obsolete cryptography

I have a apache server running and following configuration for ssl: Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains" SSLProtocol -all +TLSv1.2 SSLCompression Off ...
1
vote
1answer
59 views

Linux Kernel module signing

If the linux kernel is compiled to check for kernel modules signing, it checks the validity of the public key (X.509) w.r.t the current system time. For the first time the system is booting up, it ...
4
votes
2answers
6k views

RSA public key and private key lengths

I'm having a problem understanding the size of an RSA public key and its private key pair. I saw different key sizes for RSA algorithm (512, 1024,... for example), but is this the length of public ...
5
votes
1answer
3k views

SSH Key: Ed25519 vs RSA

A lot of people recommend using Ed25519 instead of RSA keys for SSH. The introduction page of Ed25519 (http://ed25519.cr.yp.to/) says: [..] breaking it has similar difficulty to breaking [..] RSA ...
2
votes
2answers
132 views

Are hashes of hashes used for password storage in practice? Why/why not? [duplicate]

A naive developers might store a password in the database directly, which would then be compared directly with the password sent from a client. A more security conscious developer might instead store ...
5
votes
2answers
1k views

Is HTML5 sessionStorage secure for temporarily storing a cryptographic key?

Assume I am building a local web application (e.g. browser extension) in HTML5 to encrypt a database locally. Access to the database is controlled by a password and a cryptographic master key is ...
3
votes
1answer
76 views

How can the parallelization in CTR mode be attained?

I am using CTR mode to encrypt/decrypt files. Theoretically CTR mode is faster than CFB or CBC because of its individual operations on blocks. In my case CTR mode takes almost as long as CFB. How can ...
2
votes
2answers
198 views

Can I use AES CTR mode to encrypt files with same key and nonce?

I want to encrypt the files stored in SD card and I am using the CTR mode of AES to encrypt it. The key and IV are fixed. So each time I encrypt/decrypt I use the same key and nonce. Most of the ...
8
votes
3answers
489 views

Does TLS_FALLBACK_SCSV provide blanket protection against downgrade attacks?

The TLS_FALLBACK_SCSV flag was touted as a way to prevent POODLE, which abused the potential to downgrade to SSLv3 from TLS. Does the implementation of this flag prevent similar downgrade attacks (e.g....
-2
votes
2answers
287 views

Cryptowall encryption files

This is a question concerning the way the Cryptowall ransomware encrypts files on the victim's computer. Someone knows if it is possible to recover the encryption key comparing the encrypted file and ...
1
vote
1answer
80 views

Prevent padding oracle attack on key exchange process

I found in my searches that the padding oracle attack can be used against the RSA with PKCS1PAdding or OAEP padding, and I used this algorithm for a symmetric key exchange. How can I prevent a padding ...
4
votes
2answers
101 views

Can the intended recipient be derived from a public-key encrypted ciphertext?

Assuming you have a list of possible recipients' public keys, and a ciphertext encrypted with one of those public keys, would it be possible to determine which public key?
0
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1answer
314 views

RSA: same symbols in plaintext give same symbols ciphertext?

I just started studying Information Security, but I just ran this program: http://www.sanfoundry.com/cpp-program-implement-rsa-algorithm/ and faced this strange thing. For small keys (don't try to ...
1
vote
3answers
721 views

What type of hashing method is used for the private key to encrypt for signing messages?

To use RSA for signing, Alice takes a hash of the message, encrypts the hash using her own private key, and appends the result (this is the signature) to the message. Eve can of course still decrypt ...
4
votes
3answers
162 views

GnuPG symmetric encryption yields different output

I have a use case where I want to commit symmetrically encrypted source code using GnuPG (think of Coursera assignments for backup and collaboration). I encrypt/decrypt all sources in a batch with a ...
0
votes
1answer
121 views

Analyzing a TLS connection?

Suppose I want a secure TLS communication between me and myschool.edu. Which of the following should I trust to preserve confidentiality, integrity, and authenticity. Here are the options and my ...
1
vote
1answer
764 views

Prevent CryptoLocker on Server

A quick question, which may have a not-so-quick answer - Are there any ways to prevent files associated with CryptoLocker, to be propagated to a data server, by means of a back up? We use Cobian as ...
12
votes
2answers
4k views

What are the differences between TPM and HSM?

TPM (Trusted Platform Module) and HSM (Hardware Security Module) are considered as cryptoprocessor, but what are the differences exactly? Does one of them have more advantages than another?
1
vote
2answers
202 views

Crypt-analysis methods for breaking or finding weakness in an encryption algorithm? [closed]

How cryptanalysts work on an algorithm related to diffusion/confusion factors in order to find a weaknesses in an algorithm, for example how cryptanalysts could find weakness on DES? is there methods ...
0
votes
4answers
148 views

How does PKI work for the client side?

As I send this question as a request to yahoo's server, the information in the request will be encrypted with yahoo's public key (which is available for everyone). Then the information will arrive at ...
2
votes
5answers
183 views

Does publishing the md5sum of a private key compromise the private key in any meaningful way?

If I have a 4096 DSA private key used for signing binaries, and I want to ensure that a partner has an identical server using the same private key, can I send the md5sum of the private keys over an ...
0
votes
1answer
113 views

How to get my GNUPG Elgamal private key exponent?

I have tried googling around. The closest solution I get is: private.key contains the private key file. $pgpdump -i private.key But this only gives me the following: ElGamal p ElGamal g ElGamal y ...
-1
votes
2answers
119 views

Is it a secure encoder and hasher?

I want to ask if my code secure or not. if this is not secure please tell me the reason. This code is mixed of Rjindael-256, base64_encode and SHA-512. function xencoder($input,$key) { $salt = 'Q(...
3
votes
2answers
655 views

How does a Tor exit node know the public key of the client?

When the Tor exit node executes the client's request and receives a response from the server, it must create an onion cell that can be reversely decrypted along a circuit through the Tor network. Thus,...
0
votes
1answer
243 views

Does it increase the security if we split data to n pieces and encrypt each one with different key and different algorithm?

For example: a 10 MB file will be sliced to 10 pieces (each 1 MB) and then dispersed between network nodes. Each node will encrypt it with its own key and different algorithm (AES, TwoFish, Blowfish, ...
1
vote
2answers
247 views

How can an attacker identify the encryption method with only ciphertext?

Assume that attacker only could obtain ciphertext, but knows that method is symmetric. Is there a way to find which algorithm was used for the encrytion? And in general, if attacker knows the ...
6
votes
1answer
751 views

can multiple encryption of data with multiple keys increase the security?

I mean: does encrypting data multiple times have an effect on diffusion and confusion? Does it increase security, or does it have no effect? Is it useless? Does it make it harder to break the secret, ...
2
votes
1answer
475 views

SSH: What's the difference or interplay between /etc/ssh/[host files] and ~/.ssh/[public key]

I'm new to SSH after a decade of dabbling with Ubuntu and other Linux builds. Today I successfully setup SSH, but I had a few hangups and headaches along the way. Although the system is now running ...
4
votes
1answer
543 views

Showing bank routing/account numbers, and storing them safely

EDIT: This is for the UK/Europe region. I've been scratching my head reading other posts similar to this one about safely storing bank routing and account numbers. I know that routing numbers can be ...
18
votes
5answers
1k views

How can I explain “zero knowledge proof” to an end user?

A ZKP allows proof of knowing the answer to a secret, without actually disclosing what that answer is. Is there any analogy that can help people put this concept into everyday practice? A "lie to ...
1
vote
3answers
836 views

Sharing a common public and private SSH keys for a cluster of machines

I guess this is way to settle an internal debate I am having with myself. In my provisioning process, I am wanting to share a common public and private ssh keys for each machine in a clusters, (...
3
votes
1answer
161 views

Is this symetric or asymetric encryption?

I’m at the beginning of my journey into the world of security. I am reading about the most fundamentals topics and I have encountered something unusual that has thrown me. The Conundrum: I have come ...
1
vote
1answer
59 views

Is it possible to convert a gpg key to a different encryption algorithm [duplicate]

Maybe the answer to this question is a simple and unequivocal "No", followed by "How can you possibly think that this is possible?". And if I think about it rationally this seems to be the only answer....
22
votes
3answers
2k views

What ways are there to verify a self-written protocol?

Before everyone goes yelling: "NEVER DO YOUR OWN CRYPTO", I haven't, technically (I'm still half way), but apart from that I am making a TLS-like protocol, but way lighter. I needed to secure ...
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2answers
106 views

Securing communications in decentralized network of servers

Lets consider the following setup: One has a decentralized network of servers. A single root certificate has been distributed to all servers which has been positively checked as authentic and ...
4
votes
1answer
71 views

Is is possible to avoid internal seeding of a RNG and seed the generator manually using OpenSSL's RAND_bytes()?

I'm trying to write a random number generator with the OpenSSL library. The provided RAND_bytes() function is self-seeding with the /dev/urandom. That's why I am only able to reseed with the RAND_seed(...