# All Questions

686 views

### Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
311 views

### Can you help me understand ECC Cryptography and it's algorithm?

I want to know the basic understanding of ECC algorithm for cryptography. But I am not aware of the algorithm. Can anyone provide me with a basic explanation of the algorithm?
150 views

### How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
869 views

### iSeries (AS/400) Database File: password encryption

I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except... In order to allow users to login and maintain ...
19 views

### Use $e$ in GGH as shared secret?

I was wondering if we could construct a symmetric encryption scheme by assuming that the secret key itself in GGH is public and the shared "key" is the error vector $e$. To encrypt we would take the ...
54 views

### What does $\langle A, B\rangle$ mean?

I'm reading about CL-PKC and in Al-Riyami's FullIndent, I find some notations I must be sure to understand, to well explain it ...
45 views

### Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
40 views

### tweakable block cipher and ideal block cipher

Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ?
17 views

### How do two parties put together the AUTH data in the SKEME protocol?

SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ...
22 views

### Single-scalar multiplication with sign bit

I want to know if there's an "easy" timing-free way to compute the sign of $y$-coordinate of $r G$, for a secret scalar $r$ and $G$ the generator of an elliptic curve. We have several choices for ...
25 views

### How to add passphrase to an RSA key?

If I want to protect a private RSA key, do I just XOR the password into the key, or do I do something else? Is it secure? Edit: I got a good answer from a comment - Hash the password/passphrase with ...
26 views

### Cracking vigenere of non-text cleartext

I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
28 views

### Is $E′(k,m)=E(0^n,m)$ semantically secure?

$(E,D)$ is a (one-time) semantically secure cipher where the message and ciphertext space is $\{0,1\}^n$. $E'(k,m)$ is defined as $E′(k,m)=E(0^n,m)$ The question is whether $E'(k,m)$ is (one-time) ...
60 views

### How is the block size of a block cipher related to how susceptible the block cipher is to a birthday attack?

For example what can you say about how susceptible Triple-DES is to a birthday attack due to the fact that it has a block size of 64-bits.
38 views

### How to increment the counter value for CTR mode?

I am testing CTR mode on STM32 board. I want to know how the auto increment of counter happens and what is the method to follow if I have to increment the counter manually.
52 views

### Handshake SSLv2, SSLv3, TLS

Can someone confirm that SSLv2, SSLv3, and TLS have the same Handshake process (ClientHello/ServerHello, ..., ClientKeyExchange ...)? If not, can you tell me the main differences between theses three ...
46 views

### Book recommendation about MPC? [closed]

I have hard time finding introductory book talking about details of secure multiple party computation. Is there any recommendations? Thanks for the help. Hope this is not off topic.
107 views

### tls 1.2 finished message stucture

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, ...
39 views

### Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key ...
44 views

### Can we do modulus switching for number theoretic encryption?

Can we do modulus switching for number theoretic encryption such as Paillier or ElGamal?
24 views

### Question about Cipher Block Chaining(CBC)

I'm studying at the moment the CBC Encryption method,and I was asked in an excercise how many bits would be wrong after decryption if during the transmission 2 bits are interchanged. My guess is that ...
15 views

### One time Key Encapsulation Mechanism?

For KEM's, do you only exchange a private key once via the public key encryption and then do all further encryption with this private key, or is a fresh private key sent out with each message? The ...
50 views

### Trying to udnerstand textbook sample solution

I am preparing for the final exam in my Data Security class so I am trying to read and understand the textbook's exercise questions. The sample solution at the end the textbook is more like a hint ...
44 views

### Key management and derivation - Allow changing of the passphrase

I'm working on a program, which allows encrypting files before storing it on a cloud service. Currently I'm trying to figure out how to derive and store the keys. First, I wanted to use a simple ...
39 views

### Attacks on schemes based on elliptic curves when the transmitted points are not on the curve

Some elliptic curve schemes require to send a curve point during the normal execution of the protocol. For example, ElGamal encryption and ElGamal signature require this. On the other hand, ECDSA does ...
47 views

### Using what we already know about the data to decrypt it?

Are there any methods or tools out there that let us use what we know about the data in order to crack the encryption? For example let's say I get access to an encrypted database file but I know ...
149 views

### How to crack unknown 8-bit encryption algorithm?

Can anyone tell me how to crack the encryption of 8 bit algorithm, when you have some clue that CBC mode is used, but the algorithm is secret. You also have some encrypted data (chosen plain text), ...
25 views

### Multiplexed stream cipher

Consider the stream cipher that consists of 3 LFSRs, with the output of one coming being used to determine which of the other 2 is used that clock cycle. Both the IV and the polynomials are secret. ...
41 views

### How to use AES-CBC to password-encrypt a small block of stored data

I have a small block of data (16 bytes) that I am required to encrypt, store (in an unsecure, visible location). Later I have to retrieve and decrypt it. I must use AES-CBC and a user-entered ...
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### Better security than SHA1 for signature?

An application that I maintain uses Sparkle Update to update itself. I expect attacks from high level attackers (China, USA's NSA, etc.) and have some questions about how secure the cryptography ...
73 views

### Are developers expected to implement Diffie-Hellman key exchange themselves?

I noticed that the GO standard library has some really nice functions for performing AES encryption / decryption in various modes. However, I couldn't (yet) find anything for Diffie-Hellman key ...
81 views

### Certificateless cryptography Implementation

Hello guys I am trying to implement Certificateless Cryptography algorithm with reference to this base paper. Right now I am trying to implement the code in java. ...
114 views

### Best non-digital cipher?

Is there an undisputed cipher that was considered the best before the computer age? (This is not suppose to be a discussion, it's either a yes or no.) Please give a brief description why it is yes ...
73 views

### Determine whether a given function is a pseudorandom generator/function

I am trying to solve the following three tasks (for exam practice, not as a homework): Define $𝐺 : \{0,1\}^* \rightarrow \{0,1\}^*$ by $G(x_1,...,x_n) = 𝑥_1 \oplus 𝑥_2,𝑥_1,⋅⋅⋅,x_n.$ Prove that ...
40 views

### Monoalphabetic cipher using different languages in the same plaintext

Today I learned the principle of the monoalphabetic cipher. It's simple to decrypt a ciphertext written all in the same language (english for example) because I can use the syntactic properties as ...
72 views

### Decrypt affine cipher given encryption key [duplicate]

i have a ciphertext C=TLNJG formed using the equation c=(7p+11) mod 27,c equivalent to numerical equivalent character of ciphertext and p the plaintext how do i ...
34 views

### Composite vs Prime Order Groups in Attribute Based Encryption

Reading about Accountability in ABE currently and the paper "White-box traceable ciphertext-policy attribute-based encryption supporting flexible attributes" when comparing its system with an existing ...