# All Questions

1answer
52 views

### Available programs that can verify the working of a simple substitution cipher

Is there any tool available that can test whether a simple substitution cipher is working. I will put my scenario in detail. Lets say I built a simple substitution cipher that maps 8 bit data to 16 ...
1answer
171 views

### Repeated XOR decryption [closed]

I have this message in Hex: ...
1answer
90 views

### In RSA, why does Alice's $N$ need to be relatively prime to Bob's $N$?

I was asked this by my professor and I didn't understand the reasoning behind it. If Alice has a the key pair $(p_a, n_a)$ and Bob has the key pair $(p_b, n_b)$, why do $n_a$ and $n_b$ have to be ...
1answer
370 views

### how to calculate non linearity of AES S-box?

S-box has to satisfy different design criteria. How to calculate non-linearity , propagation criteria for an AES S-box?
1answer
72 views

### Why develop new stream ciphers when block ciphers can be trivally made into streams?

I've just been reading about a new drop-in replacement for the RC4 stream cipher, but why develop new stream ciphers when AES can be made into a stream with a little XORing?
1answer
72 views

### Direct sum of Binary numbers In Mixcolumns

I have just started learning cryptography and I am trying to make sense of the direct sum on some binary numbers. I am trying to find a column of a state space after a Mixcolumns operation has been ...
1answer
105 views

1answer
179 views

### ElGamal encryption with private key [closed]

Does the encryption with a private key and decryption with a public key works in ElGamal likewise what is done when we use RSA for sender authentication?
2answers
2k views

### Multiplicative inverse in $GF(2^8)$?

I know how to do multiplication over $GF(2^8)$. Logic is... ...
2answers
218 views

### Scrypt's maximum strength to increase entropy of lame passwords

The developers claim that a 6 letter long password hashed with 3.8 second's of scrypt would cost \$900 to brute-force. If we use more cycles, how quickly will the brute force cost increase? What ...
1answer
77 views

### Authentication mechanism for low memory, low computing power device

I am looking for an authentication mechanism that works best with low memory, low computing power devices. I came across a paper "A Practical Zero-Knowledge Protocol Fitted to Security Microprocessor ...

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