2
votes
1answer
511 views

Cryptography system by combining a block cipher and a stream cipher

I have to come up with a design for a cryptography system by combining a block cipher and a stream cipher. I can't seem to come up with anything on my own. Can someone point me in the right direction ...
3
votes
1answer
217 views

Key exchange using ECDH vs ECIES

I'm a beginner to ECC crypto programming. Does any one explain to me the difference with using ECDH for shared key exchange and use of ECIES by encrypting shared key with the public key of the ...
-1
votes
0answers
30 views

Garbled table for 3 inputs

I have a truth table of a full adder with 3 inputs (A,B,Cin) and 2 outputs (S, Cout). How can I create a garbled truth table? I mean, in the general form it is ...
3
votes
1answer
236 views

what are the NTRU keysize and application in industry?

I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ...
1
vote
1answer
105 views

pairing parameters in PBC library

I would like to know what are the pairing parameters of PBC library and what are they used for? Here an example where they are used. I noticed that we can give any file in the param subdirectory. Is ...
2
votes
0answers
66 views

Ciphertext size of any CPA-secure public-key encryption scheme

I know that, for any CPA-secure public-key encryption scheme, the size of the ciphertext after encrypting a single bit is superlogarithmic in the security parameter. That is, for $(pk,sk) \leftarrow ...
3
votes
2answers
102 views

Is pseudorandom function also a one-way function?

Can I assume this? Specifically, I want to know if the following two cases are valid. Suppose $prf_k(m)=c$ One-wayness: Only given $c$, we cannot reveal $m$. Without key $k$, even given $m$, cannot ...
-1
votes
0answers
42 views

Existence of a random function under constraints

Let $F_1$ and $F_2$ be two random functions taking as input $N$ bits and returning $N$ bits. Let $C_1$ and $C_2$ two constants of $N$ bits. Is there a random function $P$ taking as input $2N$ bits ...
4
votes
1answer
849 views

What characters are valid in PGP encrypted and signed messages?

What characters may be present in a PGP encrypted message or a PGP signature? For example, do encrypted messages only use the Roman alphabet + some numbers and symbols? Can the character set be ...
2
votes
2answers
479 views

Triple-DES DUKPT CBC PIN variant vs Data variant

Does any know the difference between triple des dukpt decryption algorithm with PIN variant and Data variant? I have done Triple DES DUKPT PIN variant, which generate session key from KSN and BDK. ...
4
votes
2answers
86 views

One-way function definition

I cannot understand why a one-way function $f$ is defined in this way $\text{Pr}(f(A(f(x))) = f(x)) < \frac{1}{p(n)}$ and not $\text{Pr}(A(f(x)) = x) < \frac{1}{p(n)}$ where $A$ is a ...
1
vote
1answer
81 views

How to encrypt a vector $e\in Z^{m}$ using LWE

I have a vector $e \in Z^{m}$, now I want to encrypt it by using LWE (Learning With Errors). Because in LWE, we have to encrypt of a bit $\{0,1\}$. How can I encrypt a vector $e \in Z^{m}$?
1
vote
1answer
123 views

AES with 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 ...
2
votes
1answer
127 views

Size of a MAC for a quickly checked message?

Let suppose that we have to check a message that was written one second ago. The message is discarded immediately after having being checked. What "minimal" size for such a MAC is secure?
1
vote
1answer
284 views

Encryption schemes and pseudorandom permutations

Can an encryption scheme (deterministic or not) be viewed as a pseudorandom permutation taking as input a message and returning a value of the same bit-encoding length?
4
votes
3answers
1k views

Complexity of arithmetic in a finite field?

I am wondering what the complexities are of adding/subtracting and muliplying/dividing numbers in a finite field $\mathbb{F}_q$. I need it to understand an article I am reading.
3
votes
1answer
790 views

Linear Feedback Shift Register Taps

Linear feedback shift register tap charts are availale for registers of length 3 to 168. Does anyone have a chart for register lengths from 168 to 256 or beyond?
1
vote
1answer
107 views

Bit level permutation

Could anyone explain how secure is bit level permutation? What is the most serious threat against the security of this kind of cipher?
4
votes
1answer
111 views

OCB and GCM security

Is OCB as secure as GCM or CCM ? Since OCB design is quite different from GCM and CCM, I was wondering if the security properties of these latters are satisfied by OCB, as well.
2
votes
1answer
198 views

Requirement for the length of a HMAC tag?

I've seen NIST requirements about key length. What about the output lengths ? Is 112 bits enough for the HMAC output length ? Can we truncate the tag to keep only 112 bits ?
1
vote
1answer
219 views

Why Merkle Tree doesn't suffer Birthday attack?

I am trying to understand why Merkle Tree doesn't suffer the birthday attack? Can you help me?
1
vote
1answer
83 views

Username and Password: How does it work?

Suppose a client (Alice) goes to an HTTPS website (Bob) over TLS 1.2. Alice sends Client Hello with some random number $r_a$. Bob sends Server Hello with another random number $r_b$. Suppose they ...
25
votes
1answer
32k 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 ...
1
vote
1answer
168 views

What could be the problem with this TLS 1.2 Client Finished Message approach?

Can someone make sure I'm creating my Client finished message properly as I've been working at this for days and keep getting a Bad record MAC error and I have no idea what I'm doing wrong. First ...
0
votes
0answers
176 views

TLS 1.2 finished message stucture [duplicate]

I am implementing TLS 1.2 and using ECDHE_RSA_AES_128_GCM_SHA256 cipher suit. According to RFC 5246 finished messages have {verify_data[verify_data_length]} and verify_data = PRF(master_secret, ...
5
votes
1answer
742 views

What methods allow us to determine the language used in a monoalphabetic substitution cipher?

Working on a cipher (which I assume to be a mono-alphabetic substitution cipher due to the letter frequency) I struggle with the fact that I don't know which language the plain text is written in. ...
1
vote
1answer
220 views

Is any specific packet cipher mode to be prefered for use with – for example – UDP?

Cipher modes typically assume data is streamed or read from a reliable channel with guaranteed ordering. However, many communication transports, such as UDP, are not reliable and don't guarantee order ...
4
votes
1answer
86 views
+50

Applying machine learning algorithms to homomorphic encrypted data

I have a basic understanding of encryption and I got back to the topic because of an interesting site that encrypts financial data using homomorphic encryption (HE) and I would be happy for any input ...
2
votes
1answer
20 views

Client side encryption / hashing of “person ID's” with password?

What we're looking for A solution where data is stored and retrieved (!) from a server using a person ID that can only be known at the client (form of ...
1
vote
2answers
36 views

Secure logical AND using Ishai-Sahai-Wagner Scheme

I want to try to implement a secure AND the way it was described here: https://eprint.iacr.org/2010/441.pdf It says that there are two bits a and b and that they have been split into d+1 shares. How ...
0
votes
1answer
28 views

IND-CCA Security of a encryption scheme which is combination of two schemes

I have two public key encryption scheme $\Pi_0$ and $\Pi_1$ and one of them is IND-CCA secure, another one is IND-CPA secure. Let $\Pi$ be a public key encryption scheme, which is a combination of $\...
3
votes
1answer
80 views
+100

Is security against semi honest adversary inheritable?

I have a two party protocol, let's call it $M$. At some point, there are $k$ steps, each one involving an oblivious transfer protocol, which is known to be secure against semi honest adversaries. ...
1
vote
3answers
86 views

Is there a PRNG algorithm that allows to switch between states directly, not calling next()?

Basically I need a function with the following interface: getRandomBytes(uint128 seed, uint64 state, uint16 byteCount) Consecutive calls with the same seed and ...
2
votes
1answer
62 views

Proof that a encrypted file has the same content as an (existing) original

Assume that Alice has a file F which she is going to send, in encrypted form, to Bob. Alice possesses F and the public encryption key K of Bob in form of an X509-certificate. She generates the file E ...
0
votes
1answer
17 views

Is there a TLS extension for generating unique IVs for AES GCM?

Since reusing IVs is death for AES GCM, it seems like using the fixed IV in the TLS connection state is a phenomenally bad idea. It wouldn't even seem to be a good idea to use the salt + counter ...
1
vote
1answer
14 views

Message expansion in NTRU: why is it $\log_p(q)$-to-$1$?

Suppose that we are working with the original version of NTRU with parameters $(N,p,q,k,d_f,d_g,d_\phi)$. In this case we are working with the original NTRU with the digital envelope and the ...
3
votes
1answer
29 views

Is order of Correlation Immunity of AES S_box Zero?

I am working on AES S_box and trying to find out its properties like Correlation Immunity, Balancedness , Algebraic Degree , ANF form etc. These Papers 1, 2 give a nice definitions to above said ...
0
votes
0answers
14 views

Decoding base64 with key [on hold]

I'm working on a program that scrapes video URLs from a website. The URLs seem to be coded in base64. Here's an example: ...
1
vote
1answer
365 views

Calculating XOR Key Sizes

I've been playing around with the Matasano crypto challenges (cryptopals.com). I had a couple false-starts on the challenge that has you creating a program to calculate the key size of a XOR encrypted ...
0
votes
3answers
84 views

What is proper size of window Using RSA Window method?

I want to Use Window method for RSA modular Exponentiation. because of SCA. But I don`t know what is proper window size.
6
votes
1answer
229 views

Is it possible to determine or estimate the period for Blum-Micali PRG?

The Blum-Micali is a cryptographically secure pseudorandom number generator. The construction (from wikipedia): Let $p$ be an odd prime, and let $g$ be a primitive root modulo $p$. Let $x_0$ be a ...
1
vote
1answer
15 views

What is the structure of a Server Key Exchange Message structure when using a psk identity hint?

I need to know the structure of a server key exchange message when using a psk identity hint. I know the general structure but I can't find an example of where the identity hint fits in. Thanks.
-1
votes
0answers
12 views

Cloning limitation of PCB [on hold]

Is it possible to clone the car key remote PCB? I am not sure wether that PCB cloned can copy the program from IC.
1
vote
1answer
49 views

What is the starting point of Hellman's TMTO method?

I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space n?...
1
vote
1answer
154 views

Doubling the block length of a given block cipher

IMHO the main essence of a Feistel cipher of block length $n$ is the working of a non-linear function $F$ that is applied to the two halves of the block of length $n/2$. Now suppose a certain block ...
4
votes
3answers
240 views

Can the SHA256 hashes of consecutive integers be attacked?

Suppose that the attacker knows the SHA256 values of integers $n, n+1, n+2 ... n+k$. $n$ is sufficiently big, so we do not expect to be able to brute force $n$ just by $\operatorname{SHA256}(n)$ ...
-1
votes
1answer
28 views

How to test digital signatures between two computers?

I have to test a digital signature algorithm. I have two computers, one will be signer and the other one is verifier. I implemented both of these in C++ but I do not know how to test it. Computers are ...
3
votes
1answer
310 views

Simple digital signature example that one could compute without a computer?

I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms. There is a great question ...
1
vote
0answers
17 views

where is ANS X9.31 used?

FIPS 186-4 mentions two standards for RSA: PKCS #1 and ANS X9.31. PKCS #1 is used with SSH, X.509, etc. What is ANS X9.31 used with? FIPS 186-4 has the following line: ANS X9.31, Digital ...
1
vote
0answers
48 views

Are there any digital signatures valid for multiple pieces of data?

Are there any digital signature algorithms that can be used to produce signatures valid for multiple pieces of data? For example: Pick a private key $k_{private}$, which has public key $k_{public}$. ...

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