All Questions

122 views

Will SHA1 or Other Hash Functions Ever Contain Quotes [closed]

I feel foolish asking this, but will the hash generated by SHA-1 or other encryption methods ever have the possibility of containing a quote? Or any other characters that may be escaped such as ", ', ...
53 views

Is the half-homomorphic property of RSA a problem for blind RSA signatures?

For blind RSA signatures, is it problematic that RSA is half-homomorph? Take a scenario where blind RSA signatures are used for something like a voting procedure or this proposal: Lots of people, ...
101 views

Defence against timing attacks

I know this is a difficult subject but would a good defense against timing attacks be not sending a message if the decryption or authentication fails? So if the attacker provides a wrong HMAC for ...
128 views

How difficult is it to get a key using simple XOR

Recently someone gave me an algorithm as follows: XOR = Key XOR Random1 XOR Random2. They think that in order for someone to extract "Key" from XOR they would need Random1 and Random2.. but looking ...
77 views

Find the prime factorization in the DLP

Suppose we have $g^x \equiv h \pmod N$ Where $N = pq$ and $p$, $q$ are distinct primes. Also $(p-1)/2$ and $(q-1)/2$ are primes. If we know what $x$, $g$ and $h$ are, is it possible for us to know ...
156 views

How to compare between two cryptographic algorithms in terms of security? [closed]

How to compare between two cryptographic algorithms (e.g. SHA-1 and SipHash) in terms of security? That is, how could one prove that algorithm X is more secure than algorithm Y?
124 views

Multiple encryption of part of block

Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones: Block 1: Byte 0 - 7 Block 2: Byte ...
38 views

AES mode scheme feedback [duplicate]

I've been studying encryption on a hobby basis, and wanted to know if I got this basic cypher construction right (this is another experiment, see the AES ECB experiment thread earlier). Encryption: ...
99 views

AES key from encrypted text and VI

So I'm trying to figure out if it's possible to extract the private key if you have the ciphertext and the IV corresponding to that ciphertext. It's for some kind of a challenge, and can't really ...
51 views

AES different modulo operations

I don't get the modulo 10001 operation in mixColumns so much. If I have to take the byte computations mod 100011011 anyway what leads me to a result of 4byte length, why do I need the mod 10001 ...
105 views

Vigenere ciphers : Need help for math analysis

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
108 views

Koblitz encoding a message to a point, what is the “associated auxiliary base parameter”?

I am looking at the Koblitz method for encoding a message as an elliptic curve point. The first step given in the paper I'm reading is: "Choose an elliptic curve and its associated auxiliary base ...
425 views

How do we compute IV+1 in CTR mode?

This may be a very simple question, but I have not found info about this in any place. My question is about CTR mode: When it says $IV+1$… How do we make this operation? For example, if I have the IV ...
2k views

What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
137 views

What is the advantage of using the socialist millionaire protocol to authenticate vs HMACing some random number?

Say Alice and Bob have a shared secret $s$. Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$, where $r_1$ and $r_2$ are randomly ...
155 views

Predicting Google Authenticator OTP Codes [closed]

I use Google Authenticator to generate OTP codes for logging in. As you know, the numbers change every 30 seconds or so, and (AFAIK) use an RSA key to generate those numbers. If someone were to ...
51 views

Will the complement of a 64-bit key and message produce the complement ciphertext if ECB is used in DES?

Say I have a 64-bit message/key: P1: 1011....... K1: 0101....... I run this message/key pair through DES in ECB mode and obtain some cipher that looks like the ...
43 views

Recombination thresholds in degree reduction of multiplied Shamir shares

Shamir's secret sharing can be considered multiplicatively homomorphic, if one is aware of the fact that multiplying two shares of a (n,t)-threshold shared secret yields a share of the same secret, ...
388 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 ...
3k views

128 bit 3DES Key and AES Key: what's the difference?

Apologies if this is really basic but I couldn't find the answer to this. I have heard some Info Sec colleagues talking about creating an AES key in preference to a DES or 3DES key but I don't know ...
118 views

Is format preserving encryption suitable for use with words or names?

Is it possible to use FPE to encrypt names and language words like 'Bob' 'the' 'tree', in order to preserve both length and format (like keeping characters within a certain range like A-Z a-z) The ...
261 views

Creating serial key generator using ECDSA, how to get signature short enough?

I've written some questions in this stackoverflow and got great responses but now I'm trying to wrap it all together. I have for the last couple of weeks been building a serial key generator project ...
141 views

ccrypt and its security

I would like to know how secure is ccrypt to encrypt files (like images, videos and other non-plain text data) using single password of 20+ chars length. It uses Rijndael with 256-bit block size and ...
14k views

How does RSA signature verification work?

I understand how the RSA algorithm works for encryption and decryption purposes but I don't get how signing is done. Here's what I (think) I know and is common practice: If I have a message that I ...
114 views

Drawback of ElGamal encryption

I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ...
73 views

What are the steps to decrypt a TLS 1.1 record?

My question is related to another question in Cryptography about TLS 1.1 and 1.2. I have read both RFC 2246 The TLS Protocol Version 1.0 and RFC 4346 The TLS Protocol Version 1.1. What I know is that ...
86 views

How does ccrypt work?

On many Linux/GNU distributions CCrypt (ccrypt) by Peter Selinger is available as a command line utility to encrypt files. How does the protocol work and is it ...
68 views

Are there cryptographic schemes that mask as unencrypted traffic?

Are there cryptographic schemes that make encrypted traffic look like unencrypted traffic?
160 views

Possible hashing scheme

Plaintext(binary) : 10101100 //very short for easy understanding Suppose we have 4 predefined schemes/functions, rotate (101 -> 011) flip (1101 -> 1011) exchange (11011 -> 10111) stretch (1100 -> ...
79 views

Why would cryptography fall apart if there were a finite number of primes? [closed]

I vaguely know that prime numbers are very important in cryptography, but I assume for most encryption methods, they tend to stay rather 'small'. Are we really using massive prime numbers for ...
165 views

How secure is it to use password as AES key?

I am developing a steganography app where user encrypt any file into an audio file. The user can enter a password to protect the hidden data. The same password is converted as a 256 bit key and the ...
86 views

How obvious is it to decrypt numerics encrypted with a reused one time pad?

For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could ...
2k views

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 ...
115 views

Calculation of time needed to crack DES with my CPU

I have a laptop that has the CPU and the RAMs shown below in the images. My question is that, using this CPU and the RAMs, how much time would it take for me to crack an old school DES algorithm ...
99 views

What are the well known protocols that offer perfect forward secrecy? [closed]

As far as I know these are the well known protocols that offer PFS TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA) SSH (RFC4253) OTR (Protocol Version 3 Spec) IPsec (with IKEv1 and IKEv2) ...
134 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
1k views

Shannon confusion and diffusion concept

I read the document(not the whole document) from Shannon where he speaks about the concepts of confusion and diffusion. I read in many places(not in the document but around the internet) that ...
95 views

Multiple keys for the same ciphertext [duplicate]

Say you have a plain text: How are you today? and you encrypt it so it becomes: LKD03Loel03skj1Q03 Now you have multiple people that need to know the plain text of this cipher text but ...
77 views

I am currently working on my diploma project, a high security NFC door lock and need to exchange very sensible data. That's why I thought of PGP encryption, which is as far as I know one of the ...
100 views

Differences between Work Factor and Time Complexity

I am interested to know if work factor means the same thing as time complexity. Quoting Work Factor : Uncovering keys in cryptosystems The Work Factor of a cryptosystem is related to its ...
148 views

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 ...
105 views

Zero Knowledge Non Interactive Proof with random oracle

I am trying to write an assay about Non Interactive Zero-Knowledge proofs and would like to take the simple discrete logarithm problem example fallowing the Feige-Fiat-Shamir heuristics. I understand ...
2k views

How exactly is “true randomness” defined in the realms of cryptography?

Especially in relation to stream ciphers, I frequently read about (sometimes theoretical, sometimes practical) attacks that are able to "distinguish a ciphertext from a truly random stream". What's ...
2k views

The exact difference between a permutation and a substitution

I've noticed confusing definitions about permutation and substitution, preventing to make the difference. A permutation changes the order of distincts elements of a set, but this can be writen as a ...
93 views

What would a backdoor in symmetric key cipher look like? [duplicate]

Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but ...
88 views

Why is C_digest defined in PKCS#11?

Digesting doesn't require any key and can be performed on the client side. Why does the PKCS#11 token interface standard have a C_digest method? For example, why should I send my data to a PKCS11 HSM ...
652 views

If we can find prime numbers larger than 17 milion digits, why can't we find all 1024bit primes? [duplicate]

"Largest Known Prime Number Discovered; Has 17,425,170 Digits" http://www.sciencedaily.com/releases/2013/02/130213225424.htm If we can find prime numbers larger than 17 milion digits, why can't we ...
452 views

decrypt numbers multiplied by a certain floating point number

A friend has about 10K numbers in a an excel sheet. He wanted to encrypt these numbers in order to share the file with a 3rd party that will help him reorganize the tables. What he did, to hide the ...