5
votes
1answer
639 views

Are there any MGF1 and OS2IP functions available in C?

I need MGF1 and OS2IP functions, as defined in the PKCS #1 v2.1: RSA Cryptography Standard. Is there anything available in OpenSSL, or any other open C library?
10
votes
3answers
599 views

Does NTRU decrypt correctly now?

The NTRU public-key cryptosystem has a lot of interesting properties (being resistant to quantum computer attacks, being standardized by several important bodies), but it also has a pretty unique ...
5
votes
2answers
237 views

Is my HMAC secure if I have a complete series of HMAC'd prefix strings

Let's say I have a long sentence, like "The quick brown fox jumped over the lazy dog." Let's further say that I need to keep this string encrypted, so I use an HMAC. Let's further further say I want ...
3
votes
1answer
413 views

Is XOR in a CBC-like mode secure?

Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively. The first byte of ciphertext is computed like this: $C_{1} = K_{1} \oplus P_{1}$ ...
3
votes
3answers
2k views

Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings

I'm building a system that has to take file paths, and generate a unique name for each one. I'm planning on using SHA1 as the hash function. My question is: do I have to deal with possible collisions ...
4
votes
1answer
456 views

How were the AES key and block length subsets of Rijndael selected?

My intuition tells me it's a trade off between speed and security, but how did the standardisation process select these three seemingly arbitrary key lengths (namely, AES-128, AES-192, AES-256).
1
vote
2answers
3k views

Initialization vector length insufficient in AES

I use AES with AES/CBC/PKCS5Padding with the following encryption and decryption code sections in Java: ...
4
votes
2answers
2k views

Why DSA cannot be used for encryption?

Here it is mentioned that DSA cannot be used for encrypt. But Both RSA and DSA can be used to generate public and private keys, right? (Or am I wrong?). Then why can't I use the DSA public key to ...
5
votes
3answers
1k views

Encryption with “constant” initialization vector considered harmful

I try to get the full reasoning behind the above statement. First, after reading articles here and at wikipedia i understand that using an IV only once is good practice. For stream ciphers not doing ...
5
votes
1answer
756 views

Do Rabin Fingerprints have any advantages over CRC?

Background In both, bitstrings are interpreted as a polnomical over GF(2) and they each can be used to implement a hash over a sliding window. The definitions of each are as follows: Rabin ...
6
votes
1answer
284 views

How to enhance randomness of AES?

I'm using PHP to encrypt a string and Java to decrypt it on a remote server. To perform the encryption, I'm using the strategy that can be found here. My problem is that the strings I encrypt are ...
-1
votes
1answer
201 views

How can we find Public key have only 8 or 16bits? How many messages does Eve need to know the Public key in RSA?

Suppose Alice sends messages to Bob by encrypting the messages with Bob's public key. Eve knows that the data is encrypted using RSA, but does not know the public key. Can Eve figure out the public ...
6
votes
1answer
710 views

How can disk encryption systems (like Truecrypt) resist frequency analysis when they allow random access?

I don't understand how disk encryption (e.g. TrueCrypt) is supposed to resist frequency analysis. If blocks can be randomly accessed (which they can), doesn't that mean that frequency-domain ...
2
votes
2answers
291 views

Order of hashing concatenation

A = hash("blue" + X); B = hash("pink" + X); If A and the literals are known and X is unknown, are there attacks on B aside from the attacks on directly on hash()? ...
2
votes
2answers
369 views

Is it possible to figure out the public key from encrypted text?

Suppose Alice sends messages to Bob by encrypting the messages with Bob's public key. Eve knows that the data is encrypted using RSA, but does not know the public key. Can Eve figure out the public ...
3
votes
0answers
242 views

RSA reencryption scheme

Is there such an algorithm that would allow to upgrade the encryption of a RSA-encrypted message without revealing the plaintext to the untrusted user? Basically, such an algorithm would probably be ...
2
votes
1answer
223 views

Public Key Encryption with forward secrecy

Is there a known non-trivial system with plausibly secure public key encryption where: 1. $\;\;$ the $\:$ time $\:$ function is efficiently computable 2. $\;\;$ [pubkey,privkey] $\:$ pairs are ...
1
vote
1answer
437 views

Recovering the key in an ElGamal Signature Scheme variant

From page 318 in Stinson's "Cryptography: Theory and Practice", question 7.3: Suppose that Alice is using ElGamal Signature Scheme. In order to save time in generating >the random numbers k that ...
2
votes
2answers
293 views

How do I demonstrate that a PRNG not designed for cryptography is not suitable for generating passwords?

This is a replication of this question on Stack Overflow. There's class Random in .NET runtime which is designed for use as a cheap fast source of pseudo-random ...
2
votes
3answers
439 views

RSA finding the inverse of the public exponent

I have a very basic doubt in RSA key generation and its usage. In RSA key generation you choose two large prime numbers of a very large order. Then you multiply them.(eq $p \cdot q = N$) Now, ...
4
votes
1answer
159 views

Do public/private pairs work both ways?

Public/private key algorithms such as RSA encrypt a message with a private key but only decrypted with another (mathematically related) key. Can the public key decrypt the messages encrypted with ...
6
votes
1answer
212 views

Message space in security definitions

What is the message space in the following example and how does a message space relate to a security definition? I mean, what difference does it make to such a definition if your message space is ...
5
votes
1answer
546 views

Elliptic curves for ECDSA

i'm trying to implement parameters generation for ECDSA according to SEC1 v2.0: Input: The approximate security level in bits = t is {80, 112, 128, 192, 256} ...
6
votes
3answers
533 views

Security equivalence proofs for breaking RSA

It is my understanding that while a practical solution to the factoring problem will definitely break RSA, it has never been proven that the security of RSA is equivalent to factoring. In otherwords, ...
4
votes
2answers
629 views

What is the smallest plaintext/ciphertext size for an algorithm like?

When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
5
votes
2answers
492 views

Practical necessity of semantic security under chosen plain text attack (CPA) in CBC mode

I was not able to understand why we practically need a CPA security in Cipher Block Chaining. (which insist on having a random IV), let say if the encryption is not CPA secure i.e , the adversary can ...
3
votes
1answer
242 views

Has there been any cryptanalysis of RC4-52?

Several websites ( such as Is there a secure cryptosystem that can be performed mentally? ) briefly mention RC4-52 as a modification of standard RC4. RC4-52 has only with 52 instead of 256 elements ...
5
votes
1answer
154 views

Digital signature for an expiring password

I would like to create a publicly available tool that is used to generate a password that gives a limited time access to a resource. My idea is to digitally sign the current date with a private key ...
5
votes
1answer
203 views

One-way hash on encrypted data, result hidden from hasher

I'm looking for a one-way hash function that can be performed by A on an encrypted piece of data E(D) provided by B, without the performer A able to figure out D or H(D). This similar to HMAC(Message, ...
6
votes
3answers
2k views

How does the key schedule of Rijndael looks for keysizes other than 128 bit?

It said in Wikipedia that: [....] Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The blocksize has a maximum of 256 bits, but the ...
6
votes
1answer
516 views

A fair peer-based coin-flipping protocol?

I found this question on the game programming site and was intrigued. I came up with an answer off the top of my head but I'm no cryptanalyst so it is probably not water-tight. This is how my idea ...
18
votes
4answers
1k views

How to fairly select a random number for a game without trusting a third party?

Several people are playing a game with random events and require a way to produce a random number. (Such as dice rolls or a lottery.) Can this be done such that each player has the power to be ...
7
votes
2answers
637 views

Does AES have any fixed-points?

Is there any pair of 128-bit strings M and K such that AES$_K$(M) = M? If yes, how do I go about (efficiently) finding such a pair?
6
votes
1answer
671 views

What causes first block of AES decryption to be garbled, even with correct IV?

I am attempting to duplicate wireshark's packet capture decryption for a TLS HTTP session, where I control the private key of the server. The cipher suite number is 0x00002f, TLS_RSA_AES_128_CBC_SHA ...
7
votes
1answer
432 views

CBC key lifetime, or, “how big is too big?”

IPSec recommends rekeying SA's figuring in both time and amount of data sent. Even when using AES-256 in CBC mode, the key and IV commonly get re-negotiated after 100MB. My case isn't using IPSec, ...
7
votes
1answer
770 views

In which situations is a length-extension attack a problem?

A lot of hash functions, including the SHA-2 family(but not the SHA-3 candidates and SHA256d) are vulnerable to length extension attacks. But when is this property a problem? I guess certain naive ...
2
votes
1answer
1k views

How to sign a message using RSA?

Assuming I already have a D, P, Q, etc of an RSA key: How do I now sign a message? If it matters – the message is around 100 bits. I don't know much about cryptography, but I can get these numbers ...
3
votes
3answers
218 views

Are asymptotic lower bounds relevant to cryptography?

An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
1
vote
1answer
315 views

Existing dictionaries of popular words to help solve a random substitution cipher?

I'm trying to find faster ways to solve this: http://cryptogram.org/solve_cipher.html Actually lists of common words are good, but they are often limited to 1000 words. I found this, but I'm not ...
1
vote
0answers
61 views

cipher text only attack - how to know when to stop when brute-force attack? [duplicate]

Possible Duplicate: How can I do a brute force (ciphertext only) attack on an CBC-encrypted message? My question is about a cipher text only attack - I have as input only the initialization ...
4
votes
1answer
172 views

Question about hash collisions

If we have a hash function $h(x)$ and then a hash function $H(X) = h(h(X_0) || h(X_1))$ where $X_0$ is the first half of $X$, $X_1$ is the second half of $X$ and $||$ is concatenation. Then assuming ...
5
votes
1answer
264 views

Is it safe to encrypt a public key alongside a message with AES?

If I have a message M and a public key P, and I encrypt them alongside one another: CIPHER = AES(M + P, aes_key) Is CIPHER now weakened if someone knows what P ...
5
votes
1answer
278 views

Can a digital money system exist, that's secure, anonymous and allows offline transactions?

I just read Offline anonymous electronic money systems and their cryptographical base , which asks for anonymous offline systems. The OP claims eCash is such a system, and the answer claims that ...
8
votes
3answers
969 views

Is it okay to use a hash of a timestamp as the IV for AES?

The message format includes a datetime field in the clear. Is it okay to also use this field (or some hash thereof) as the initialization vector? In this case, CBC is the mode being used.
8
votes
1answer
510 views

XSL on serpent and rijndael - which is most affected?

So I've often looked at serpent and thought it was a very strong contender in AES. Not so long ago I was looking for evidence as to why it didn't beat rijndael. So far, the closest I've got answering ...
3
votes
1answer
327 views

Blind signature with openssl

I'm trying to understand (to reproduce in practice) how does blinded tokens work. Currently i'm lacking examples. According to Wiki the blinded signature protocol is the same as ordinary signature ...
1
vote
1answer
168 views

ID-Secret Scheme

I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present. Party 1 and Party 2 hold some credentials, an ID and a Secret. Party 1 Creates this message: ...
1
vote
1answer
189 views

Block ordering and security in a MAC?

To authenticate a message $m = m_1 \,\|\, \dots \,\|\,m_n$ the tag $t := F_k(r) \oplus F_k(m_1) \oplus \dotsb \oplus F_k(m_n)$ is used, where r is uniform random number $(0,1)^n$ and $m=(0,1)^n$. Even ...
4
votes
1answer
536 views

Is this authenticated one-way communication protocol secure?

I am looking to see if this one-way communication protocol is secure. Assume Alice wants to send Bob a message (and doesn't need Bob to reply in the same session/channel - think email). Bob knows ...
1
vote
1answer
58 views

Proving item association without revealing one of the associated items

I'm a total noob when it comes to cryptography but I believe this falls under the "zero knowledge" category. I have two associated pieces of information: tag — known by both parties. Unique per ...

15 30 50 per page