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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Consequences of tampered /etc/ssh/moduli

What are the consequences if an attacker is able to modify the /etc/ssh/moduli file?
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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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Why don't people hash and salt usernames before storing them

Everyone knows that if they have a system that requires a password to log in, they should be storing a hashed & salted copy of the required password, rather than the password in plaintext. What I ...
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4answers
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NSA Suite A Cryptography: Security through obscurity?

What is the opinion of scholars, cryptographers on NSA Suite A? Containing unpublished algorithms. Could it really be that much better than the published algorithms besides being obscure and not ...
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9answers
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What cryptographic algorithms are not considered secure? [closed]

What cryptographic algorithms are not considered secure, but yet are still widely used and available in standard libraries? If applicable, mention a secure alternative.
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How does RSA encryption compare to PGP?

On this answer ck says RSA and PGP are different. What you are essentially asking is how do I run my petrol car on diesel? The answer is you can't. I would be interested in a more ...
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Shouldn't GPG key fetching use a secure connection?

If I run this for example: gpg --keyserver hkp://keyserver.ubuntu.com --recv-keys 0xFBB75451 then does the importing occur in a secure way? I mean does it go over only secured connections? (HKP?) ...
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How would you store a 4 digit pin code securely in the database?

I'm familiar with password hashing, using salts, bcrypt etc. But it doesn't seem like this would work to store a 4 digit pin code since the attacker could try all 10,000 combinations quite quickly. ...
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Secure Configuration of Ciphers/MACs/Kex available in SSH

Following on the heels of the previously posted question here, Taxonomy of Ciphers/MACs/Kex available in SSH?, I need some help to obtain the following design goals: Disable any 96-bit HMAC ...
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3answers
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Convergence - an SSL replacement?

Today, Moxie Marlinspike, a security researcher famous for his research on Android and SSL and related protocols (author of sslstrip/sslsniff), released "Convergence" which says is "an agile ...
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What is a cryptographic oracle?

I came across the term "cryptographic oracle" and despite a bit of googling I was unable to come across a clear, concise definition. What is a cryptographic oracle and what does it do? Can anyone ...
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What's the practical limit for rainbow-table based bruteforce?

Say we have a hash of a password. The password can be considered to be made of of totally random characters and has a fixed length of N. The hash is SHA1(password+salt), where the salt is of length M. ...
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Cracking a linear congruential generator

I was recently listening to the security now podcast, and they mentioned in passing that the linear congrunential generator (LCG) is trivial to crack. I use the LCG in a first year stats computing ...
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5answers
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Can ECC be used without infringing on patents?

Can ECC (Elliptic Curve Cryptography) be safely used without infringing on Certicom's patents? I would like to make use of ECC in an embedded system to establish a secure channel. But, I am concerned ...
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2answers
4k views

Is HTTP compression safe?

The CRIME attack taught us that using compression can endanger confidentiality. In particular, it is dangerous to concatenate attacker-supplied data with sensitive secret data and then compress and ...
21
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1answer
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Has SHA-3 Arrived?

I know NIST called for contenders (in 2007) regarding the new hash algorithm to replace SHA-2. Has there been a selection, or finalists selected?
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2answers
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Is “real salt” the same as “initialization vectors”?

In the question about real vs. fake salt, the answers describe how real salt 'perturbs the encryption algorithm.' I know roughly how initialization vectors work; is this the same concept, or something ...
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5answers
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PCI Encryption Key Management

(Full disclosure: I'm already an active participant here and at StackOverflow, but for reasons that should hopefully be obvious, I'm choosing to ask this particular question anonymously). I currently ...
21
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1answer
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Timing attacks on password hashes

Timing attacks can have a devastating impact in scenarios where the secret is involved, often in cases where byte-wise array comparison is used. Now there are those that advertise using constant ...
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6answers
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What are the good use cases for disk encryption?

I've been researching disk/file system encryption, and on the surface it seems like a good idea for a lot of things. But as I dig further, the security it offers seems more mirage like than real. ...
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What are the chances to generate the same ssh key?

I could generate ssh keys on the client like (without password): ssh-keygen -b 8192 -t rsa -f /home/THEUSER/.ssh/id_rsa -P '' -v and copy the generated id_rsa.pub to the server: ssh-copy-id -i ...
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2answers
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Is it okay to sign a PGP key without an IRL meeting?

[PGP] can get paralyzed by excessive analness. — Phil Zimmermann Preamble I am in the process of building my own web of trust. That is, I want people (PGP users…) to be—fairly—sure that, by ...
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3answers
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How long should a random nonce be?

NIST provides good guidelines on the length of keys and hashes for various algorithms. But I don't see anything specifically on the length of a random or pseudo-random nonce (number used once). If ...
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2answers
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Why is it always `HASH( salt + password )` that we recommend?

Browsing over this site, many forums, online articles, there's always one specific way we're suggesting to store a password hash: function (salt, pass) { return ( StrongHash(salt + pass) ) } But ...
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3answers
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What specific padding weakness does OAEP address in RSA?

It's been recommended to use OAEP when padding messages to be encrypted via RSA, to prevent known plain text attacks. Can someone elaborate this in better detail? I'd specifically like to know the ...
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What is the actual value of a certificate fingerprint?

In a x509 digital certificate there is a "certificate fingerprint" section. It contains md5, sha1 and sha256. How are these obtained, and during the SSL connection, how are these values checked for?
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How big should salt be?

I will be using scrypt to store passwords in my application. As such, I'll be using SHA-256 and Salsa20 crypto primitives (with PBKDF2). Having that in mind, how big salt should I use? Should it be ...
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Homomorphic encryption used for e-voting?

I was reading wikipedia about homomorphic encryptions, and one part got me a bit confused: "The homomorphic property of various cryptosystems can be used to create secure voting systems, ..." ...
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1answer
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WPA significantly less secure than WPA2?

I understand at least theoretically WPA2 is more secure than WPA, but in practice does it make any difference which one you use? From what I know there are no known attacks for either except for ...
18
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6answers
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Principle of asymmetric algorithm in plain english

I was giving a presentation to my colleagues about cryptography basics in which I explained about asymmetric algorithm and its use. One of the common question from the audience about asymmetric ...
18
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5answers
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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 ...
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3answers
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What is the difference between “key length” and “bit strength”?

On occasion, I hear the terms "key length" and "bit strength" used interchangeably. Are these the same things? Or are they different?
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3answers
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MySQL OLD_PASSWORD cryptanalysis?

The password hash used for MySQL passwords prior to version 4.1 (now called OLD_PASSWORD()) seems like a very simple ad-hoc hash, without salts or iteration counts. See e.g an implementation in ...
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Whats the difference between MAC vs hash

What is the difference between the two algorithms? One difference that I know of, is that MAC is keyed and hash is not.
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4answers
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Generate cryptographically strong pseudorandom numbers in Javascript?

Is there any good way to generate cryptographically strong pseudorandom (or true random) numbers in Javascript? The crucial requirement: if a.com's Javascript generates some random numbers, no one ...
18
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1answer
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Collision rate for different hash algorithms

Is there any collision rate measure for popular hashing algorithms (md5, crc32, sha-*)? If that depends only from output size, it's quite trivial to measure, but I suppose that depends also of ...
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4answers
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IPsec (Internet Protocol Security) facts

Internet Protocol Security (IPsec) is a successor of the ISO standard Network Layer Security Protocol (NLSP). What are the advantages, disadvantages, other interesting facts regarding the protocol?
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Describe an example of indistinguishability obfuscation or functional encryption

As described in Perfecting the Art of Sensible Nonsense, a major breakthrough in cryptography research was published in the summer of 2013: Candidate Indistinguishability Obfuscation and Functional ...
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1answer
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Where do I get prime numbers for Diffie-Hellman? Can I use them twice?

I realise it's very hard to generate suitable prime numbers and generators for the Diffie-Hellman key exchange. What is the best way to generate them? And if I have one, can I use it twice? ...
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Flaw in encryption through pseudorandom number stream (from PGP documentation)

I was reading PGP docs and came upon a part written by Phil Zimmermann (PGP's creator) that piqued my curiosity: When I was in college in the early 70s, I devised what I believed was a brilliant ...
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5answers
618 views

What concrete parameters can I change to make my passphrase-protected private gpg key more secure

There are several questions which discuss the resistance of passphrase-protected private gpg keys against brute force attacks. It seems, this kind of discussion could go on forever. Rather than ...
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5answers
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Rainbow table concept for Prime numbers

Is there a concept where pre-computed tables can be used for prime number factorization ? Is it possible that a computer can generate millions of prime numbers, store it and then effectively determine ...
17
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1answer
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4096 bit RSA encryption keys vs 2048

Where do 4096 bit RSA keys for SSL certs currently stand in terms of things like CA support, browser support, etc? In the overall scheme of things is the increased security worth the risk of 4096 bit ...
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2answers
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Does my PGP key really need to match the e-mail address for which I'll be using it?

In considering whether or not I want to join the big web o' trust and put my keys on a key server, I got to thinking about how it would affect my e-mail address' exposure. I generally try to keep my ...
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4answers
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Is it dangerous to publicly share ciphertext?

Alice wants to share a message with Bob, but Alice and Bob can never be in the same place at the same time. We can assume they both know each others public keys (or agreed on a shared key, if that ...
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What are the differences between MD5, SHA and RSA?

MD5 tools output hexadecimal values. In the same manner, do SHA and RSA together produce a hexadecimal (or any other) output? What are the differences between the MD5, SHA and RSA algorithms?
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How quickly can these password schemes really be beaten?

If you use a quick hashing algorithm like MD5 or SHA-1 to hash passwords and you don't use any salt at all, how quickly could one expect a hacker to find my password out? If I use a truly random salt ...
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Multi-tenancy, SSL Certificates, and Subject Alternative Name

The X509 specification allows a CA to issue a single certificate for multiple hostnames, by using the "Subject Alternative Name" extension. From the spec: The subject alternative name ...
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What happens when an Intermediate CA is revoked?

Currently I'm working on a certificate manager that allows our product to securely connect to remote webservices (over TLS/SSL). For security, we use Certificate Revocation List checking (or ...
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In what ways does Full or Partial Homomorphic Encryption benefit the cloud?

Can someone explain, in plain English, the practical ways FHE and PHE can be leveraged in the cloud? Some interesting (and confusing) links include this Microsoft Research PDF and this wiki entry. ...