# All Questions

40 views

### Error propogation in CBC mode

Going through the wiki for modes of operation I see that the section error propogation says that an error in one block in the ciphertext in CBC mode only impacts two blocks. I do not quite get that. ...
39 views

### How to make sure the pre-agreed information safe for DH-Key Exchange

The definition of DH key exchange was given as the method let two authenticate each other & exchange the crypto key over an insecure channel. DH-key-exchange was innovated to defence ...
62 views

### How do they implement MAC in TLS?

I recently read questions about "MAC then Encrypt/Encrypt then MAC" which made me curious about how they actually use the algorithm. MAC only calculated once either case (according to what I read). ...
147 views

### cryptography and use of python programming language [closed]

why is it recommended to write cryptography programs ,for example crypt-analysis projects with python programming language? what is the advantages of python? why not use c or any other language?
46 views

### What's wrong with this “order-preserving MAC” function?

Please note: this is purely a thought experiment and not intended for any real-world usage! I came up with a simple function $\mathrm{OPF}$ to map the integers $[0,C)$ (where $C$ is the "ChunkSize") ...
30 views

### In Needham Schroeder key distribution what happens if responder's part is not encrypted in step 2 with Kbs but encrypted instead by Kab in step 3

The Needham-Schroeder protocol is: 1 A→S:A,B,Na 2 S→A:{Na,B,Kab,{Kab,A}Kbs}Kas 3 A→B:{Kab,A}Kbs 4 B→A:{Nb}Kab 5 A→B:{Nb−1}Kab Here Na and Nb are nonces. Kab is the key between a and b Kas is ...
115 views

### Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
40 views

### Affine encryption function

Let $f(x) = ax + b$ be an affine encryption function. $a$ and the cardinal of the field of our keys $K$ (in English, 26) must be coprime so that the encryption ...
105 views

### Regain 3DES ECB key, assuming I have both encrypted and decrypted text

Let's assume I've encrypted some text with some 24-byte key using 3DES ECB. Question: is it possible to regain the key if I have both encrypted and decrypted text? Excluding bruteforce.
76 views

### Hypothetical question about AES output

Consider that you stumble upon 5 different AES output strings. One of these strings can be decrypted with a secret phrase, the other four strings are based on the real string but have had random parts ...
79 views

### Assuming that we had a way of finding primes, could RSA be used without computers?

I once asked a question "Would RSA make sense if we used no computers?". The answer was negative, because finding primes that would make secure keys would prove too hard. Assuming that we had found ...
134 views

### How do I cryptanalyze a password field?

In a PostgreSQL database, I can see the following fields in a table (for a specific record): User = administrator Password = "ceMv9Me6go" Now the following are true: The password length is not ...
736 views

### Learning to encrypt/encryption algorithms [closed]

I am a beginning programmer interested in coding an application of my own to encrypt sensitive files of mine. For example: lists of passwords, bank accounts, Credit Card numbers etc. I was wondering ...
101 views

### Why is it said that if we know few bits of pseudo random sequence we can predict the whole of it?

I am new to this cryptography and in the source from which i study it is said that if we know the first few bits of a pseudo random sequence we can predict the whole of it.How is it possible? The ...
352 views

### How to calculate cycles per byte [closed]

Sometimes, websites and scientific papers that introduce and/or handle cryptographic algorithms also provide speed-analysis and tables comparing the individual performance of cryptographic ...
767 views

### How does the rand() function in C work? [closed]

I want to know how rand() works (even when I don't provide any seed how it produces PRNs?) thanks!
202 views

### What are alternatives to the random oracle model for modelling hash functions? [closed]

I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as ...
120 views

### Cryptographic Primitive Method

Is there any cryptographic primitive bijective (one-to-one and onto) function for creating cryptographic tools like symmetric encryption/decryption, Hash code generator, MAC, HMAC and Random number ...
38 views

### PGP message integrity : How can receiver of an email check the integrity using the sender's public key?

PGP message integrity: Basically, only private key can decrypt message encrypted with public key. But in the message integrity service in PGP does the reverse, where the Hash of the message if ...
51 views

### Pseudo Random Generator with fixed Hamming Weight [closed]

I'm searching for way to generate secure pseudo random sequence with a fixed Hamming weight using a seed. I found below code but I need a seed to generate a sequence ... (and need know if is possible ...
79 views

### How Does Progressive Hashing Work?

Example: http://jsfiddle.net/KGtUE/ https://code.google.com/p/crypto-js/#Progressive_Hashing sha256.update("abc"); sha256.update("def"); sha256.update("ghi"); ...
49 views

### How small are we talking about when defining the small public/private key exponent [duplicate]

I've been wondering about the 'small' part of the attacks on RSA, like the small public key exponent and the small private key exponent and what's not really clear is how small are we talking about? ...
70 views

### Reverse engineering a single checksum byte [closed]

I am working to understand a system which saves a few bytes of data together with what appears to be a single checksum byte that provides a very naive guarantee that the data has not been tampered ...
52 views

### How can the key size be calculated [closed]

If the decrypting key is 448, then what is the key size? Suppose I am encrypting a plain text with a key by choosing some random numbers between ...
120 views

### PRG existance and P versus NP

how can we prove that if there is a secure PRG then P!=NP or in reverse order?(is there any reduction?) a secure PRG is a pseudo random generator that for every eficient (running in probabilistic ...
83 views

### Symmetry for finite cyclic groups (Z/pZ)∗

How well is it known that for $i$ such that $1 \leq i \leq \frac{p − 1}2$: $$g^{i+(p−1)/2} = g^{i−1+(p−1)/2} − g^i + g^{i−1} \pmod p$$ Whilst working in the finite cyclic group of prime moduli ...
75 views

### PRF and hash functions

Is there a difference between PRF and a hash function? example: Creation of a secret key is using PRF and creating a secret key is using hash function.
233 views

### How can I convert numbers into prime numbers?

I'm working with one-way accumulators, but I'm not knowledgable in cryptography. Is there an easy peasy way to hash numbers (or whatever) into prime numbers? Obviously I'd like it to be collision ...
51 views

### Positioning of keys in encrypted text

I'm just looking at very simple encryption. I've noticed that the key is typically either at the front or at the back of the encrypted text. This is quite easy to break if you know the key. It can ...
65 views

### encrypting data signals using the time variations between two independent coupling functions [closed]

There was a recent article about a new encryption technique that encrypts "using the time variations between two independent coupling functions". What is this technique they are referring to?
54 views

### How to create PSK key? [closed]

I'd like to create a PSK key to use with TLS-RSA-PSK-WITH-AES-256-CBC-SHA - what is the format of this key?
128 views

### Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
107 views

### Number of possible keys in a Play fair cipher [duplicate]

So for the play fair case, the number of possible keys is : 26x26 = 676 possible keys But if we consider the repeated letters, how many unique keys will the play fair have? I mean how will ...
65 views

### Adding “salt” to “doHash” function in Java [closed]

For one of my university projects I am being asked to "Improve the code to satisfy the pre-image resistance requirement." Basically the program is a basic encryption server system, and when I type a ...
102 views

### Need Help Reversing my Encryption Algorithm [closed]

So I wrote a simple encryption algorithm (Not very secure, just a starting point. I don't want criticism on it.) and I have been having trouble finding a way to decrypt the text. The algorithm is here ...
105 views

### How to determine which type of crypto is used in a text file? [closed]

is there a tool or a way to determine which type of crypto is used in this type of text: ...
97 views

### Are the protocols DH-EKE, B-SPEKE, A-EKE, and SRP are considered challenge-response authenticaion mechanisms? [closed]

I got confused which one is considered challenge-response mechanism which one is not.
70 views

### Substitution Cipher Help [closed]

I have the following ciphertext: w jaoot zhoipqjwp ql wee lro oawxaop I know it is a substitution cipher but using my frequency analysis skills does not help me to find the plaintext. I think the ...
206 views

### why RSA uses Semiprime numbers? [duplicate]

Why does RSA use semiprime numbers? Why not just use any big number ?? What is the advantage of the two original numbers being prime? Because factoring any big number will be difficult
81 views

### Use of Different keys with PCBC

Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones ...
74 views

### Paillier Crypto System : Pros and Cons? [closed]

Can you please list the pros and cons of the Paillier crypto system you have encountered or found?
97 views

### Can someone explain how this unpadded RSA formula works?

Taken from http://en.wikipedia.org/wiki/Homomorphic_encryption, $\mathcal{E}(x_1) \cdot \mathcal{E}(x_2) = x_1^e x_2^e$ $\bmod\; m = (x_1x_2)^e \;$ $\bmod\; m = \mathcal{E}(x_1 \cdot x_2)$ What is ...
71 views

### Is size Q equal to size SHA(Q)? [closed]

Assume d is a 128 bit random integer and P is base point of an elliptic curve and Q = dP is a point on the elliptic curve and SHA is a hash function with 128 bit output, my question is: Is size Q ...
69 views

### The specification of modern, non-communicating cipher machinery [closed]

I'm looking for references, papers or guidance on a class of system which I have not seen widely discussed. Consider powerful electronic machinery which remains in the custody of communicating ...
882 views

### AES: keylength and password length? [closed]

What is the difference between the keylength and the length of a password for AES-256?
143 views

### Integer factorization via geometric mean problem

presume: we have A and B integers, and C - product of multiplication of A and B, A and B are prime numbers (strong or usual) G - is geometric mean of A and B (square root of C) also, we have: if B > ...
134 views

### Which areas in CS will be (or have been) most affected by fully homomorphic cryptography? [closed]

I'm in the middle of planning a 5000ish word essay on fully homomorphic cryptography, the current practical implementations and their limitations. Which areas of CS as a subject have been (or will ...
296 views

### Is triple des similiar to RSA in that they message size is limited to the key size?

Is triple des similiar to rsa in that the message size you can encrypt is limited (unlike AES)? Yes you can break the message size into parts and apply it, but I'm not interested in doing that so I ...