Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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Are there any known weaknesses with ElGamal algorithm?

I am working on a messaging system and plan to use ElGamal asymmetric encryption to protect the message contents during storage and transmission. (This would be in addition to TLS used during ...
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Why does OpenSSL append extra bytes when encrypting with aes-128-ecb?

Plaintext: Attack at dawn!! Hex: 41747461636b206174206461776e2121 Key: ...
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Is the following symmetric design secure?

Assume: $O$ be a reversible random permutation oracle on a finite set and $O^{-1}$ the inverse permutation (pretty much equivalent to a random permutation: What is the difference between a bijective ...
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How many keys does the Playfair Cipher have?

I was just studying the Playfair cipher and from what I've understood, it is just a slightly better version of a Caesar cipher, in that it isn't actually mono-alphabetic but rather the 'digrams' are ...
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Can I use PBKDF2 for authentication and decryption?

I want to store a hash for authenticating a password. I also want to use the same password for decryption. Can I use PBKDF2 for both? (I plan to use different salts for the authentication and the ...
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Should RSA primes p and q differ in length by “a few digits”?

When generating RSA keys in the original RSA paper it is stated: to gain additional protection against sophisticated factoring algorithms, p and q should differ in length by a few digits Why is ...
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175 views

Can Alice send Bob a secure message with only DSA and no key exchange?

Suppose Bob has a DSA key pair, and Alice has Bob's public key. Is there any secure way that Alice can send Bob a message only he can read if Bob can not send any reply? I think the answer is no, ...
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557 views

Is Chaocipher a secure cipher under ciphertext-only attack?

Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ...
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214 views

Should different key pairs be used for signing and encryption?

In the recent iOS Security white paper from Apple (February 2014), the section on iMessage discusses using two different asymmetric key types as part of its standard operation: When a user turns ...
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336 views

Can two people with different one time pads securely exchange a message like this?

Alice has a message, generates a one time pad, encrypts her message and sends it to Bob. Bob generates his own one time pad, encrypts the message again, and sends it back to Alice. Alice then decrypts ...
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Why is it said that if we have a duplicate ciphertext block it can leak our information?

I have been recently going through a question: http://security.stackexchange.com/questions/15767/what-do-key-size-and-block-size-mean-in-cryptography and it created in me a series of doubts. Referring ...
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518 views

What is 'security margin'?

I have been academic papers about Rijndael, Serpent, and Twofish, and there is this term that is vague to me. I cannot find a tangible definition in google. Can someone briefly define, describe, and/...
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What happens if an RSA key pair has identical public and private exponents?

Rather, is it possible for big prime numbers? Classroom examples usually involve smaller primes, so for example if you are given a prime number pair $p = 3$, $q = 13$ you would get $n = 39$ and $e = ...
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Encryption algorithm that produces dummy output on incorrect passwords

Background: I've been thinking about using encryption in the context of backing up files to untrusted locations (to the point of making the file publicly and widely distributed for practically ...
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How do I solve this RSA instance for m?

How we can solve this equation and get the value of M? $$8 = M^{13} \mod 33$$ not a computer program, but a mathematical operation.
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Decrypting DES with decrypted and encrypted data [duplicate]

I got two 8-byte strings. One which is decrypted is: FF FF FF FF FF FF FF FF and one which is encrypted is: ...
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Leading 00 in RSA public/private key file

I found these following values ALWAYS have the leading 00 in public/private key, public key: modulus private key: modulus, p,q, d mod (p-1), d mod (q-1), coefficient e.g., modulus ...
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218 views

How can I break this encryption scheme?

Let $p$ be a large public prime. Alice holds a private key $(e_1,d_1) \in Z_{p-1}^*$ such that $e_1 d_1 = 1 \mod {p-1}$. Bob also holds a different private key $(e_2,d_2)$ with the same property. Let'...
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RSA cipher wrong use

Why is it foolish if you decide to use an RSA cipher to encode some message by first converting each letter of the message to an integer? So for exmaple Space=0, a=1, b=2,... After the conversion I ...
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Which crypto libraries/programs do we have the most confidence in? [closed]

I have recently begun studying crypto. If it's one thing I have learned it's that we should not implement our own crypto. Therefore we should look to using existing software and libraries. When I ...
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Security considerations on “expand 32-byte k”-magic number in the Salsa20 famility of stream ciphers?

I'm currently examining the NaCl library written by Daniel J. Bernstein and I noticed that the library hard codes the sigma: ...
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What are some good references for the implementation weaknesses in RSA

I'm pretty sure I understand textbook RSA. Choose p and q, large primes, and compute n=pq. Choose e such that $gcd(\phi(n),e)=1.$ Publish n and e. Compute d such that $de=1$ (mod $\phi(n)$). To ...
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FIPS 140-2 Compliant Algorithms

Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES". Any suggestions would be much ...
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I need an opinion of encryption method I thought of in High school

First, I'm really not into cryptography, but have some basic knowledge. This was a thought experiment (and later exercise for my programming skills), but even though it was long time ago and I tried ...
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309 views

Why does RSA give better security on longer messages?

I am trying to understand the notion of RSA security. Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long. If the ...
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366 views

What does 0…0 and 1…1 mean

I am very new to cryptography but can someone explain what exactly does 0...0 and 1...1 mean in general term. Is it that 1st and ...
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Decrypting an encrypted text out of order

Does there exist a cipher that can be encrypted twice with two different keys and then decrypted twice using either key first? For example: ...
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Cryptographic system with double keys with reversible order

While reading Shamir, Rivest and Adleman's paper on "Mental Poker", I've met a mention of system such that $E_a(E_b(x)) = E_b(E_a(x))$, without however disclosing details on it, with $E_a(x)$ being “...
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Encryption of small messages

Some time ago, I asked how to encrypt small messages like e.g., four decimal digit numbers (banking PINs). I've got my answer, but also a warning like it makes no sense as it's easy to guess: Even ...
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Can we proxy-re-encrypt using homomorphic encryption schemes?

Homomorphic encryption schemes are PKE schemes with an additional special method Evaluate. The Evaluate method takes input any function (as boolean circuit) and encrypted inputs of the function and ...
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Searchable Encryption with Substring Search

I want to search substrings in encrypted string. To do that I have read “Implement Rabin-Karp Algorithm” and “Substring-Searchable Symmetric Encryption”. After that, I completed the Rabin-Karp ...
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287 views

How does Microsoft's BitLocker Recovery Code work?

I don't trust Microsoft BitLocker because it is closed source, which makes it so people can't audit it. But now I'm really interested in how its recovery code works. In my own knowledge, encrypted ...
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188 views

When/why is RSA (hybrid) encryption used rather than alternatives?

I've read that RSA is not meant for encrypting large plaintext because: (Are these also true for other public-key encryptions like ElGamal?) It is slow. Padding makes the ciphertext blocks much ...
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Picking a nonce in the context of CCM (CTR with CBC-MAC) mode

After having read the RFC 3610: Counter with CBC-MAC (CCM) and the Wikipedia article on CTR mode, I'm not sure how a nonce should be picked. The RFC says: A nonce N of 15-L octets. Within the ...
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Twofish vs. Serpent vs. AES (or a combo)

I've seen some posts and info online, but they are from 2009, 2010, 2011 or 2012, which is 3-6 years ago, which is a very long time. So I'm looking for an up-to-date answer about which of these is the ...
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ZIP 2.0 encryption bruteforce attack

I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password. The password was written on a paper slip, but I remember that it consisted of 30+ ...
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Back up an information as $n$ pieces and require exactly $n-1$ to recover it

Let $X\in \Bbb F_2^p$ be some information. How do I create $Y_1,\dots,Y_n \in \Bbb F_2^q$ so that having less than $n-1$ of the $Y_i$s gives you no information on $X$ but having $n-1$ of them allows ...
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Secure AES Key Generation via Salsa20?

I am not creating my own cryptography or anything, but to learn about the Dos and Donts of cryptography, I am looking into AES encryption and ways to generate keys for that. As far as I've understood,...
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Security of tokenization of plain text conversations - cryptanalysis

I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
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How does a key wrapping like RFC 3394 secure my cryptographic keys?

So I'm messing around in the BouncyCastle library with the RFC 3394 AES Key Wrap engine and I'm trying to understand the benefit of it. The problem I'm running into is how to store keys securely on a ...
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Is it ever safe to use encryption with compression?

In the wake of compression-based side-channel attacks like CRIME and BREACH, are there any safe ways to combine compression and encryption? The JWE Specification was finalised almost 2 years after ...
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How hard is the Solitaire cipher to crack?

Assuming your deck is completely random and that it is not retrivable, how hard would it be for a casual person to decrypt a message encrypted with the Solitaire cipher?
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Formal relationship between encryption and random number generators?

Cryptographically secure random number generators seem to have similar properties to symmetric encryption: initial seed is permuted to produce a random numbers (key and ciphertext) given the seed, ...
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Question about the definition of a perfect cipher

I need to prove that the following encryption scheme is a perfect cipher: Let $p$ be a prime. The secret key is a pair $(a,b)$ sampled uniformly at random from $\mathbb{Z}_p^* \times \mathbb{Z}_p$. ...
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How are state wiretaps obtaining plaintext from encrypted transmissions?

According to the US 2011 Wiretap Report, encryption — on the off chance that it is encountered — has been no hurdle to retrieving the content of a conversation. Public Law 106-197 amended 18 U.S.C....
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Does the Biclique attack on AES pose a credible risk to its security?

I have heard a lot about the biclique cryptanalysis research on AES, which as far as I know is the closest anyone has got to breaking AES. Exactly how close did they get? Does this attack propose a ...
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Storing Credentials for a Third Party

(Originally posted to SOF, but I got no answers) I am designing a small application for use inside my company. My application needs to connect to a third party website on behalf of my application ...
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Client and server using same SSL certificate - any issues?

I'm working on software where multiple components will communicate with each other using SSL. There would be one central component acting as a server, which would also require the clients to present ...
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How to communicate authentication tag for GCM?

I have written some code to do AES in GCM. I currently manually append the tag property to the ciphertext, is this the proper way to communicate the authentication tag?
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Is this streamable combination of encryption and MAC secure?

I want to combine encryption and MAC. For encryption I use AES-256 with CBC and PKCS5Padding. For MAC I use HmacSHA512. I use the Encrypt-then-Mac approach (calculate MAC over the ciphertext and ...