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Hello! My question rather splits into two sections:
Is AES correctly implemented in the .net Framework?
-
If not, are there any reviews of implementation mistakes that would weaken the security of AES (e.g. against timing attacks)?
Error-checking with hash-then-encrypt
-
I have a file i wish to transmit (encr... |
My question rather splits into two sections:
* Is AES correctly and security implemented in the .net Framework?
Are there any reviews of implementation mistakes that would weaken the security of AES (e.g. against timing attacks)?
* Error-checking with hash-then-encrypt
I have a file i wish to transmit... |
These types of cryptographic primitive can be distinguished by the security goals they fulfill (in the simple protocol of "appending to a message"):
- **Integrity:** Can the recipient be confident that the message has not been accidentally modified?
- **Authentication:** Can the recipient be confident that the ... |
Do any non-US ciphers exist? |
I'd like to create a database of questions and answers so that an attacker with access to the database can't obtain either the questions or the answers.
If `H0` and `H1` are secure hashes, looking up the answer to a question might proceed as follows:
lookup(H0(question)) -> value
H1(question) XOR value -... |
I'd like to create a database of questions and answers so that an attacker with access to the database can't obtain either the questions or the answers.
If `H0` and `H1` are secure hashes, looking up the answer to a question might proceed as follows:
lookup(H0(question)) -> value
H1(question) XOR value -... |
In the abstract of [this][1] paper at the end of the 3rd paragraph the authors say
> In both schemes we rely on the linear assumption over bilinear groups.
What is the linear assumption ?
How do you break this linear assumption ?
I would appreciate if somebody could give me concrete examples.
[... |
What does the linear assumption over bilinear groups mean? |
How do you use the Tiger hash function with GPG? |
I would like to ask what happens if we build an RSA system with modulus a product of more than 2 primes, for example let $n=p_{1}p_{2}...p_{L}$. I know only the classical RSA system with $n=pq$ with $p$ and $q$ large prime numbers.
I guess the modulus $n=p_{1}p_{2}...p_{L}$ will be not a good idea, because one can us... |
The answer is *yes*, non-US ciphers exist and are in fact very popular.
Actually, some who are looking for alternatives, opt for non-NSA/NIST ciphers, for instance Salsa/ChaCha from DJB (who is US citizen).
A lot of ciphers have been developed in EU and Japan.
China definitely has developed ciphers for its own use,... |
How do I know if a given curve requires a FpCurve F2mCurve or ECCCurve? |
Scenario 1: Encryption
----------------------
Maybe you have just WBC crypto that does decryption (i.e. inver cipher function) and slowly (WBC crypto tends to be fairly slow)?
In this case you can easily decrypt, but cannot very easily encrypt.
If you were able to find out the key it would make encryption easie... |
Salesforce recently announced they are moving away from HMAC SHA256 to RSA SHA256. Why did they make that move?. Any technical factors?
Is HMAC really easy to break?
![enter image description here][1]
https://login.salesforce.com/help/pdfs/en/salesforce_summer13_release_notes.pdf
PS: I am not a security exper... |
I am reading "Biclique cryptanalysis of the full AES" paper. What do they mean by *"sharing active S-boxes"*? How can this concept can be advantageous to make a bicycle? If there is someone who reads this paper, please explain it to me. |
The answer is *yes*, non-US ciphers exist and are in fact very popular.
Actually, some who are looking for alternatives, opt for non-NSA/NIST ciphers, for instance Salsa/ChaCha from DJB (who is US citizen).
A lot of ciphers have been developed in EU and Japan.
China definitely has developed ciphers for its own use,... |
Consider a secure modern block cipher like AES/Serpent/Twofish.
I hear everyone say that the complexity is 2^128 for a 128 block cipher.
But isn't the weak link the actual hashed and salted password? Any brute force should be targeted at it?
By my rough calculations 2^128 = 84^20, so any proper password compos... |
The weak link is the password? |
Are there any known timing attacks (both practical and theoretical) on any implementations of the following?
1. ECDSA (I'm aware of [this one][1] - are there any applicable to prime fields?),
2. ECDHE (again, over a prime field),
3. AES,
4. SHA2
[1]: http://eprint.iacr.org/2011/232.pdf |
Consider a secure modern block cipher like AES/Serpent/Twofish.
I hear everyone say that the complexity is `2^128` for a 128 block cipher. But isn't the weak link the actual hashed and salted password? Any brute force should be targeted at it?
By my rough calculations `2^128 = 84^20`, so any proper password compo... |
There is vast literature on [timing attacks on AES][1], but to the best of my knowledge no such attack on SHA-2 or any construction that uses SHA-2 (e.g., HMAC-SHA256).
[1]: http://scholar.google.com/scholar?hl=en&q=timing%20attack%20aes&btnG=&as_sdt=1,5&as_sdtp= |
I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here :-).
1) My friend said that when he used public key cryptography in the past, he used to keep his public key private too. Only giving it out to people that reall... |
It seems the only specified CTR mode ciphers in TLS are all GCM based.
GCM ciphers run `AES-CTR` and do encrypt-then-MAC with a MAC based on Galois-field arithmetic (`GHASH`) - and the latter seems to be difficult to get right in software (side-channel attacks, constant time) or require CPU hardware support (e.g. In... |
What is wrong with AES-CTR-HMAC-SHA256 - or why is it not in TLS? |
It seems the only specified CTR mode ciphers in TLS are all GCM based.
GCM ciphers run `AES-CTR` and do encrypt-then-MAC with a MAC based on Galois-field arithmetic ("GHASH") - and the latter seems to be difficult to get right in software (side-channel attacks, constant time) or require CPU hardware support (e.g. In... |
Using
openssl s_client -host myserver.net -port 443
I can see the cipher negotiated is indeed using `ECDHE` for session key exchange:
SSL handshake has read 5894 bytes and written 447 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Sec... |
With OpenSSL and ECDHE, how to show the actual curve being used? |
It seems the only specified CTR mode ciphers in TLS are all GCM based.
GCM ciphers run `AES-CTR` and do authenticated encryption with a MAC based on Galois-field arithmetic ("GHASH") - and the latter seems to be difficult to get right in software (side-channel attacks, constant time) or require CPU hardware support ... |
Given that a TLS client and server have already agreed upon ECDHE for session key establishment, how does the selection of the **actual elliptic curve ("domain parameters") being used** for deriving the DH keys work?
Is the curve somehow negotiated and if so how does that work (in the context of TLS)? |
With TLS and ECDHE, how does curve selection work? |
I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here :-).
1. My friend said that when he used public key cryptography in the past, he used to keep his public key private too. Only giving it out to people that reall... |
The question is subjective in nature, and this comment is also subjective. It was too long to leave as an actual comment so I'm posting it as an answer, although it isn't really an answer, it's a comment. This is for posterity, I guess -- this thread is already high in Google searches.
[NaCl][1] is probably the most... |
I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, Android & maybe even Windows ports will eventually exist). The question is how to make the crypto library as portable as pos... |
The question is subjective in nature, and this comment is also subjective. It was too long to leave as an actual comment so I'm posting it as an answer, although it isn't really an answer, it's a comment. This is for posterity, I guess -- this thread is already high in Google searches.
[NaCl][1] is probably the most... |
I've had lots of practice adding points for my crypto class. However I've run into a situation where I need to subtract two points for decryption:
Pm + kPb - nb(kG) = Pm
Where Pm is the plaintext, Pb is participant b's public key, nb is participant b's private key, G is a base point in the elliptic group Ep(a... |
Subtracting a point in elliptic curve cryptography? |
In the abstract of [this][1] paper at the end of the 3rd paragraph the authors say
> In both schemes we rely on the linear assumption over bilinear groups.
What is the linear assumption ?
How do you break this linear assumption ?
I would appreciate if somebody could give me concrete examples.
More sp... |
Using
openssl s_client -host myserver.net -port 443
I can see the cipher negotiated is indeed using `ECDHE` for session key exchange:
SSL handshake has read 5894 bytes and written 447 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Sec... |
Using
openssl s_client -host myserver.net -port 443
I can see the cipher negotiated is indeed using `ECDHE` for session key exchange:
SSL handshake has read 5894 bytes and written 447 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Sec... |
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.
1. 1. When I go to implement something that needs data security, there are many options -- openssl, mcrypt, truecrypt, crypt, py... |
Related to "[Is it possible to derive the encryption method from encrypted text?][1]".
Given ciphertexts generated by any of the major asymmetric ciphers ([RSA][2], [ElGamal][3], [ECC][4], etc..) can these ciphertexts be distinguished from random noise? Justify why, why not?
That is do the major asymmetric ciph... |
Are any of the major asymmetric ciphers distinguishable (EG, RSA, ECC)? |
I am aware that MD5 has a known collision vulnerability and should not be relied upon when uniqueness is required, but in the environment I am working on I only have access to MD5 hash function. Background detail below, but in general **how much and how bad is the change in the probability of hash collision if I remove... |
In the abstract of "[Cryptography with Tamperable and Leaky Memory][1]", at the end of the 3rd paragraph, the authors say:
> In both schemes we rely on the linear assumption over bilinear groups.
What is the linear assumption ? How do you break this linear assumption ?
I would appreciate if somebody could gi... |
In information theory, entropy is the measure of uncertainty associated with a random variable. In terms of Cryptography, entropy must be supplied by the cipher for injection into the plaintext of a message so as to neutralise the amount of structure that is present in the unsecure plaintext message. How it is measur... |
Generally, algorithms based on discrete logarithm specify that private keys are chosen as scalars between 1 and the order of the group (denoted $q$ here). For instance IEEE P1363 and FIPS 186-3 both specify this range for DL private keys. Is it a problem if the key is not uniformly chosen from this range?
One possib... |
So according to [Wikipedia][1] unbalanced feistel ciphers provide greater provable security. Specifically, they state:
> The Thorp shuffle is an extreme case of an unbalanced Feistel cipher in which one side is a single bit. This has better provable security than a balanced Feistel cipher but requires more rounds.
... |
Currently I'm implementing a PRNG for an embedded system. Using the [RFC 4086][1] I've decided to use the X9.17 - to be more specific the successor X9.31- standard to implement my PRNG. X9.17 uses DES, but X9.31 uses AES!
Now I need to specify the value of the AES key for X9.31. I know that at least my AES key must... |
I have been reading the question "[What is a white-box implementation of a cryptographic algorithm?][1]" and it led to this [short article / Q&A][2] which states in question 2:
> Q2: What is the difference with code obfuscation?
> Related and
> complementary techniques for protecting software implementations bu... |
> White-box cryptography is aimed at **protecting secret keys** from
> being disclosed in a software implementation.
A cryptography algorithm gets the key and plaintext(encryption mode)/ciphertext(decryption mode) as input and outputs the ciphertext/plaintext.
A white box implementation of the cryptography algorit... |
What is *"preimage resistance"*, and how can the lack thereof be exploited?
How is this different from collision resistance, and are there any known preimage attacks that would be considered feasible? |
If you had to implement BGN, how would you do it?
I'm looking for an implementation of the public-key cryptosystem due to Boneh, Goh, and Nissim (aka [BGN][1]), or at least some suggestions on implementing it myself. My goals are to explore/learn/play around with its structure, and, eventually, to produce some kind ... |
If you had to implement the BGN Cryptosystem, how would you do it? |
Are there any known collisions for the hash functions SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512?
By that, I mean are there known values of $a$ and $b$ where $F(a) = F(b)$ and $a ≠ b$? |
> **Possible Duplicate:**
> [Is SHA-512 bijective when hashing a single 512-bit block?](http://crypto.stackexchange.com/questions/301/is-sha-512-bijective-when-hashing-a-single-512-bit-block)
<!-- End of automatically inserted text -->
Is there any guarantee that there are no collisions for all 512-bit input... |
What exactly is the base for the KECCAK (SHA3) claim that a security strength of 256 bits is "post-quantum sufficient"? |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
Is there an example of two known strings which have the same MD5 hash value (representing a so-called "MD5 collision")? |
I'm reading the paper "[Message Freedom in MD4 and MD5 Collisions: Application to APOP][1]" about finding collisions for the MD5 hash algorithm involving the concept of tunnels as described in "[Tunnels in Hash Functions: MD5 Collisions Within a Minute][2]".
But I couldn't understand about the difference between poi... |
I want to calcuate the [CRC32 algorithm](http://www.libpng.org/pub/png/spec/1.2/PNG-CRCAppendix.html) using polynomials directly but I don't know how. I found the generating polynomial listed here https://en.wikipedia.org/wiki/Cyclic_redundancy_check. This corresponds to `0xedb88320` in the example code.
Can someone... |
The traditional authenticated DH protocol with PFS against active adversaries, ensures that the compromise of both party's long-term private keys after the session is completed will not help the adversary to compute session key, even adversary gets involved in the generation of messages.
<br>
An ID-based key-exchange... |
The traditional authenticated DH protocol with PFS against active adversaries, ensures that the compromise of both party's long-term private keys after the session is completed will not help the adversary to compute session key, even adversary gets involved in the generation of messages.
<br>
An ID-based key-exchange... |
Let $G:\{0,1\}^{*} \mapsto \{0,1\}^{*}$ be a secure PRG. Prove or disprove that the following construction also yields a secure PRG.
$$G'(k) = G(k||0),$$
where $||$ denotes the concatenation of two strings.
I understand that proving/disproving such constructions usually involves a proof by reduction or a counterex... |
I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here :-).
1. My friend said that when he used public key cryptography in the past, he used to keep his public key private too. Only giving it out to people that reall... |
I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here :-).
1. My friend said that when he used public key cryptography in the past, he used to keep his public key private too. Only giving it out to people that reall... |
I'm reading the SSL specs here.
The interesting thing seems to be that RC4 is not re-keyed with a new IV for each message. The stream cipher state is simply carried over to the next record. Why is this secure? Shouldn't messages be encrypted with different IVs? Honestly, this is one part I don't fully understand abo... |
I'm currently trying to understand the difference between the Long term key and the Session keys.
I'm currently studying the secret key, and under that there's a "Long-term" key and a "Session key"
what's the difference? |
The problem you're likely to encounter is that most real-world hash function attacks will be collision attacks, because collisions can be found with at least $2^{n/2}$ efficiency (or better, if the algorithm has a known weakness.) Preimage attacks don't necessarily have to have such a tidy relationship with the size o... |
I've added a few comments already so I decided to write answer to this question.
Your friend sounds like 'The Crypto Nut' from a [XKCD][1] strip. :^)
Public Key
----------
First of all, public key cryptography does not protect the public key.
Thus, trying to keep public key secure does not provide better secur... |
How can I prove/disprove that a construction yields a secure PRG? |
Can you give me an example of…
1. An attack which has second preimage resistance, but not collision resistant, and
2. an attack which has preimage resistant but not collision resistant?
I have looked at Rogaways paper but it seems complicated, hence was wondering if a succinct example exists. |
Are there any examples of attacks on hash functions which:
1. break collision resistance but not second preimage resistance, or
2. break collision resistance but not preimage resistance?
I have looked at Rogaway's paper<sup>1</sup>, but it seems complicated, hence was wondering if a succinct example exists.
... |
Are there attacks that break collision resistance but not preimage resistance? |
I'm currently studying the secret key, and under that there's a "Long-term" key and a "Session key".
What's the difference between the Long term key and the Session keys? |
What's the difference between the Long term key and the Session keys? |
Can you give me an example of…
1. An attack which has second preimage resistance, but not collision resistant, and
2. an attack which has preimage resistant but not collision resistant?
I have looked at Rogaways paper but it seems complicated, hence was wondering if a succinct example exists. |
I'm currently studying secret key cryptography, and I've come across the terms "long-term key" and "session key".
What's the difference between these two kinds of keys? |
What's the difference between the long term key and the session keys? |
I am reading the "[Biclique cryptanalysis of the full AES](http://research.microsoft.com/en-us/projects/cryptanalysis/aesbc.pdf)" paper. What do they mean by *"sharing active S-boxes"*? How can this concept can be advantageous to make a bicycle? If there is someone who reads this paper, please explain it to me. |
Can I use SHA1 as license key? |
I'm reading the SSL specs, and it seems that the initial handshake has no authenticity protection at all. What is to prevent, say, an attacker from overwriting the "available ciphers" list with one that is full of broken, or even null, ciphers? Is there some sort of defense for this, or is this fundamentally unsolvable... |
How does SSL secure the initial handshake? |
A theoretical question:
1) Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely recover the key?
2) What about if we know the key length? (I assume that we'll need plaintext with the same length of the key). |
Are there any examples of attacks on hash functions which:
1. break collision resistance but not second preimage resistance, or
2. break collision resistance but not preimage resistance?
I have looked at Rogaway's paper<sup>1</sup>, but it seems complicated, hence was wondering if a succinct example exists.
... |
Are there attacks that break collision resistance but not preimage resistance? |
Are there any examples of attacks on hash functions which:
1. break collision resistance and second preimage resistant, or
2. break collision resistance and preimage resistant?
I have looked at Rogaway's paper<sup>1</sup>, but it seems complicated, hence was wondering if a succinct example exists.
<sub><sup... |
The way *Applied cryptography 2ED* explains the puzzle is as follows (I paraphrase it):
1. Bob generates 2^20 messages of the form ``x,y`` where ``x`` is a puzzle number and ``y`` is the secret key. Both ``x`` and ``y`` are different for each of the one million message. Encrypt each message using symmetric cipher wi... |
Why does Merkle's Puzzle requires Eve quadratic complexity of effort to break the system? |
I am working on bent functions that are of interest in cryptography. I developed an algorithm that construct such functions. However, I need some tools to calculate boolean expression from the truth table. Is there such a application or applet available?
I didn't find right tag (please help me in tagging). |
Consider a secure modern block cipher like AES/Serpent/Twofish.
I hear everyone say that the complexity is $2^{128}$ for a 128 block cipher. But isn't the weak link the actual hashed and salted password? Any brute force should be targeted at it?
By my rough calculations $2^{128}$ = $84^{20}$, so any proper passwo... |
I am interested in what conditions are necessary and sufficient to define a cryptographically secure pseudo-random number generator (CSPRNG).
Wikipedia lists two defining characteristics:
1. It satisfies the next-bit test.
2. It withstands 'state compromise extensions' - part of all of the state being compromise... |
I am working on bent functions that are of interest in cryptography. I developed an algorithm that construct such functions. However, I need some tools to calculate boolean expression from the truth table. Is there such a application or applet available? (Actually I am interested in expressions without any NOTs)
I d... |
What Dan Boneh says is not a formal definition as you want it. Let me quote [Rogaway][1] on this:
> In cryptographic practice, a collision-resistant hash-function (also
> called a collision-free or collision-intractable hash-function) maps
> arbitrary-length strings to fixed-length ones; it’s an algorithm
> $H:\{... |
When you are using a named curve like P-256 in openSSL, is there any standard key size for ECDH private key keys? <br>If you look at the ec_key.c file in the openssl source this is what you see.<br>
BN_rand_range(priv_key, order)<br>
Here a cryptographically strong random number is generated which is smaller than the... |
There is already a question asking http://crypto.stackexchange.com/questions/10829/why-initialize-sha1-with-specific-buffer/10857, and my question follows on from this:
__Why are the initial states of hash functions often non-zero?__
For most, I have been able to find a clear explanation of where the initial values... |
Why does SHA-1 initialise with a non-zero state? |
A theoretical question:
1. Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely recover the key?
2. What about if we know the key length? (I assume that we'll need plaintext with the same length of the key). |
What is the limit of plaintext required to break the Vignère encription? |
There is already a question asking http://crypto.stackexchange.com/questions/10829/why-initialize-sha1-with-specific-buffer/10857, and my question follows on from this:
__Why are the initial states of hash functions often non-zero?__
For most, I have been able to find a clear explanation of where the initial values... |
What is the limit of plaintext required to break the Vigenère encryption? |
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