2
votes
1answer
252 views

AES-CTR-256 Sub Keys With Encrypted Sub Key Index

I was working with some encryption and I decided to put a spin. To preface this would be used to encrypt multiple files. You start with a key file generated from random data. For example you could ...
3
votes
1answer
566 views

AES VS PRNG+HASH+XOR

I was thinking of doing symmetric encryption using just hashing and simple XOR encryption. It would work as: Alice and Bob share a symmetric key Alice manages to send an (authenticated) IV to Bob ...
3
votes
1answer
243 views

Security equivalent to Diffie–Hellman problem?

I've been doing the security proof for one of my Theorem. Basically, given $g^a$, $g^b$, $g^{cb}$, $g$ and $c$ as known values. Is the problem of computing $g^{acb^{-1}}$ equivalent to the Diffie ...
3
votes
1answer
485 views

KDF based on HMAC-SHA-256

Is KDF based on HMAC-SHA-256(Hashed Message Authentication Code, Secure Hash Algorithm) algorithm a suitable option to generate symmetric key from the secret key? What is the basic funda, behind ...
14
votes
2answers
3k views

Is it safe to seed a random number generator from system time?

It seemed to me that the Bouncy Castle SecureRandom class for C#/.NET only uses DateTime.Now.Ticks as its seed by default. I ...
1
vote
1answer
148 views

Rate my idea: is that a stronger GPG-like algorithm?

I came up with a simple idea but I don't know if it is really secure or not. I know that you shouldn't create any algorithm on your own. I'm just curious, that's all. Algorithm explanation: First ...
9
votes
4answers
1k views

Predicting PRNG given some of its previous output

I a have a question about PRNGs and this is my very first experience with them. I have the following generator that takes a 56-bit seed $p$ during initialization and then chooses both $X$ and $Y$ ...
1
vote
1answer
90 views

Process of dividing 168bit key into 56bit keys in TripleDES

I used TripleDES so many times but never thought about this. In TripleDES it requires 168bit ...
7
votes
6answers
1k views

Generate Elliptic Curve Private Key from User Passphrase?

I'd like to generate a private elliptic curve key from user input like pass phrase. Is the best way to do this with a key derivation function like PBKDF2? Is there a better way? Edit (based upon ...
4
votes
1answer
113 views

Turning PRPs in PRGs with a counter

I am following the Coursera Cryptography I course and I have the following question, I am a bit perplexed by the statement, in week 2 lecture "What are block cyphers?" that a counter-mode PRF is a ...
2
votes
2answers
260 views

OCB nonce usage

I've just come across this piece of code in Bouncy Castle's implementation of OCB Mode: ...
2
votes
1answer
111 views

Is it possible to deduce the value of a string when given its hash and multiples hashes of the string + other known strings?

To be clear, I have access to $H(S)$ and as many $H(S||K)$ as I want. Every string $K$ is known. Can I use the extra information to my advantage and try to deduce $S$, without requiring bruteforce? Or ...
2
votes
3answers
499 views

Can a EC private key be derived from a public key?

I understand that the public key does not expose the private key. That is not the question. The question is: Given a EC public key, can a different, but plausible and functional private key be ...
1
vote
1answer
327 views

Importance of salt when deriving an encryption key

I'm very curious to know this and a bit confuses too: Suppose, I have two files encrypted using AES-128bit with keys PBKDF2-derived from the same password and the same salt. If an attacker does ...
2
votes
2answers
507 views

Polynomial representation of the affine part of the AES S-box

I have been reading up on the polynomial representation of the AES Sbox (PDF: “Essential Algebraic Structure Within the AES” by Murphy and Robshaw) and I can't get it to produce the correct output. ...
2
votes
1answer
126 views

LFSR and Markov chain question [closed]

This may seem an elementary question about LFSRs, and their link to Markov chains. LFSRs show Markov chain behaviour in that there can be a transition matrix defined over the LFSR, this follows from ...
1
vote
0answers
93 views

Attacks on Full TripleDES [closed]

I have been reading about attacks and many of them work on specific rounds of TripleDES but not on full TripleDES. Is there any attack except brute force that works on full TripleDES? (theoretical)
4
votes
1answer
72 views

Are HMACs based on hashes with larger bit-lengths also more secure?

When doing encrypt-then-mac, I can choose to use a hmac as the MAC. For example, I could use a hash like SHA-256 or SHA-512 (by using it as a keyed hash) to create that HMAC. Does it increase ...
2
votes
2answers
671 views

How secure is using a pad (using xor) on a encrypted data, for the purpose of obfuscating/hiding the underlying encryption?

Edit: I know this isn't really a one time pad (as pointed out), though I don't really know what to call it aside from just a pad, I guess. I have been reading around (mostly various stackexchange ...
8
votes
1answer
303 views

Is there a cryptographic function or system in which it becomes HARDER to break as time passes?

Is there a function or system which is time depending in which the effort required to brute force the decryption increases with time? It is easy to break encryption from many years ago because ...
8
votes
3answers
1k views

Modes of operation that allow padding oracle attacks

It seems to me that padding oracle attacks are mainly a concern for users of CBC mode encryption. Question: are any other modes of operation vulnerable to padding oracle attacks? And if so, why? ...
2
votes
2answers
217 views

Given $g$, $b$, $g^{ab}$, is finding $g^a$ a hard problem?

As in the title, given $g$, $g^{ab}$ are big elements in a prime group $Z_p$ and $b$ in prime group $Z_r$ ($p > r$, $g$ is one generator of $Z_p$). $a$ is unknown and also in $Z_r$, is finding ...
2
votes
2answers
201 views

Storing encryption key

It's my first time using stackexchange! So, I am doing a password manager in Java. But now I am VERY confused because of the encryption. There will be the program login, where the user types its ...
-4
votes
2answers
212 views

pairing-based schemes

some authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve group) is about 1000% more efficient than a pairing based one I would ...
3
votes
2answers
2k views

How long does it take to crack PBKDF2?

How much time will it take to crack PBKDF2 while using a 9 character password? I'm not specifying any specific system or platform. If a brute force attack is made using the best ever super computer ...
8
votes
3answers
3k views

How vulnerable is the C rand() in public cryptography protocols?

I just learned about the basics of public cryptography a few weeks ago and I am curious as to why the C rand() function should not be used for crypto schemes. For example, say I want to generate a ...
2
votes
1answer
289 views

How to find which padding method is used in Block cipher(AES) encyption?

I have a cipher text which is encrypted using AES128 Algorithm. I want to know the following things to decrypt the cipher. IV (Initialization Vector) Padding Method Encryption Key How do I find ...
6
votes
1answer
952 views

Using GMAC for Authentication without encrypting the message

I am pretty new to cryptography and have a sample of GCM mode of operation for AES. PFB the code ...
1
vote
2answers
251 views

Decryption issue with self-coded AES-128

I have written my own AES-128bit implementation in Java, till yesterday I thought it would be alright. (I was working on the encryption) Now I’m trying to decrypt my encrypted cleartext, but this ...
2
votes
2answers
202 views

Collecting entropy: can I use timing of reading as a separate source from the reading itself?

I'm implementing an entropy gathering program. For that I collect 2 bits from two gpio-pins connected to a random source. I whiten this stream of bits using the von Neumann decorrelation algorithm. ...
3
votes
1answer
180 views

Attack on DSA modification with bad hash function

Given a (bad) modification of DSA where the hash function is the identity ($H(m)=m$), I am now supposed to design an attack. So $(m, (r,s))$ are given and I should be able to create a legit signature ...
6
votes
2answers
1k views

Does having a known plaintext prefix weaken AES256? [duplicate]

I plan on storing data, encrypted with AES256, where the first dozen bytes are known plaintext. ('Hello World!' for example.) Does having this known plaintext prefix weaken AES256? I do not care ...
2
votes
1answer
657 views

CBC-MAC length extension attack with IV simulation

I'm doing Matasano's challenges and struggling with second part of 49th problem where I'm asked to do the length extension attack with CBC-MAC without IV manipulation. There is a hint that I can ...
3
votes
2answers
7k views

How to distribute session keys in public key cryptography?

In public key cryptography we can also use session keys which are symmetric. How do the sender (say a server) provides this session key information to its clients? If the sender (here server) ...
6
votes
2answers
306 views

Is it safe to reuse ECDH asymmetric keys for authentication?

Alice, Bob, and Carol each generate ECDH keypairs. Alice and Bob establish a communication channel and negotiate an AliceBob secret. The question is: Is it safe for Alice and/or Bob to reuse their ...
5
votes
3answers
343 views

Leak-proof protocol: is such a thing possible?

Is it possible to design a protocol that by itself guarantees that a malicious implementation cannot leak secret data without breaking the protocol? Setting: Alice and Bob have a pre-shared secret ...
3
votes
1answer
131 views

Galois field step in XEX mode

I'm reading through the XEX mode spec, and I want to make sure I've understood the $\alpha^j$ step correctly: $X = E_K(I) \oplus \alpha^j$ $C = E_K(M \oplus X) \oplus X$ where: $M$ is the ...
4
votes
1answer
161 views

Which version(s) of SRP are in ISO/IEC 11770-4:2006?

I am on the impression that SRP emerges as the least uncommon and best analyzed protocol for authentication and key agreement based on a short password. This states that SRP is part of IEC 11770-4, ...
1
vote
0answers
137 views

A question about elliptic curves and finite fields in bilinear pairings

Based on what mentioned in the paper "Pairings For Cryptographers" http://www.sciencedirect.com/science/article/pii/S0166218X08000449 the two inputs of a pairing map are two members of two additive ...
1
vote
0answers
141 views

How does AES-CCM work in BitLocker?

I'm studying this white-paper: http://jessekornblum.com/publications/di09.pdf The author says that using AES-CCM with the external key (highlighted in green at page 9, figure 4) and with the nonce at ...
2
votes
0answers
104 views

Protocol: Coin Flipping over phone

Protocol: Coin Flipping over telephone Hypothesis: Alice and Bob have agreed: a one to one function $f$ which is easy to compute $f(x)$ from $x$ and while given any value $f(x)$ it is nearly ...
8
votes
2answers
1k views

How does recovering the public key from an ECDSA signature work?

It is possible to recover the public key from an ECDSA signature (R,S). Please explain me how this works.
5
votes
2answers
1k views

How to account for moore's law in estimating time-to-crack?

It seems to be common practice (at least in some communities) to tack on the phrase "with current computing power" when estimating the absurdly long time it would take to, for example, brute-force an ...
2
votes
2answers
250 views

What is the entropy per Diceware word if a random symbol is inserted into a random position in the word?

On the Diceware page is this little gem: For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at ...
-1
votes
3answers
148 views

Could I use an hashing function for Symmetric encryption? [duplicate]

I know there are way better and more tested encryption methods, but I was wondering if the following code could be use for symmetric encryption? ...
2
votes
1answer
94 views

mixing two asymmetrical random number generator streams

Knuth describes in "the art of computer programming part 2" an algorithm called "M" for mixing two streams of random numbers. This can be used to mix random number streams giving the assurance that ...
3
votes
2answers
580 views
4
votes
1answer
113 views

Clarification of the terms “brute force” and “guess”

In the answer to the question “What exactly is a negligible (and non-negligible) function?” There is a part in the explanation that – as far as my knowledge goes – is conflicting: But instead of ...
2
votes
1answer
588 views

generate hash of all handshake messages for verify data (DTLS)

I am trying to create a DTLS client finished packet, where I need to generate verify data for handshake hash is need. And here I want to know how to generate handshake hash. As of now I am doing like ...
2
votes
1answer
701 views

What is the usual block cipher mode that goes with CTS

I am wondering: what is the most common, or most used, block cipher mode used that goes with CTS (CypherText Stealing)? Is it ebc or cbc?

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