## Top new questions this week:

### Why should I use Authenticated Encryption instead of just encryption?

There are various different modes of operation for block cipher use, some of which provide "encryption" and some of which provide authenticated encryption. Why should I use an authenticated …

encryption modes-of-operation authenticated-encryption

### Do test vectors ensure a cipher is free of backdoors?

If a cipher implementation passes unit tests using test vectors from some trusted source (these for AES, for example), then can we say that it is fully conforming to the specification, and must have …

backdoors test-vectors

### AES column mixing and S-Box confusion

I am trying to understand the AES encryption algorithm. I know that we process 128 bits at a time for a 128 bit key in a 4x4 octet form, but am confused by the following: How does the substitution …

aes cipher s-boxes mixing-function

### File Hash of Encrypted File

Simple question. I have a source file and I have encrypted it with a certain public key. If I take this exact same source file, encrypt it with the exact same key a few hours later would the file hash …

hash file-encryption

### In RSA, why is it important choosing e so that it is coprime to φ(n)?

When choosing the public exponent e, it is stressed that $e$ must be coprime to $\phi(n)$, i.e. $\gcd(\phi(n), e) = 1$. I know that a common choice is to have $e = 3$ (which requires a good padding …

rsa modular-arithmetic

### What are the pros/cons of using symmetric crypto vs. hash in a commitment scheme?

In a commitment scheme, are there any differences on using a symmetric cipher versus using a hash? If at the "opening", I have to reveal $r$ (a random number concatenated with the messaged at the …

hash symmetric commitments

### How is an AES Encrypted Message Decrypted with Random Padding?

One thing I was surprised to learn about AES is that random padding can be added to the message to make it a multiple of block size. What I can not wrap my head around is how this random padding can …

## Greatest hits from previous weeks:

### Google is using RC4, but isn't RC4 considered unsafe?

Why is Google using RC4 for their HTTPS/SSL? \$ openssl s_client -connect www.google.com:443 | grep "Cipher is" New, TLSv1/SSLv3, Cipher is RC4-SHA Isn't RC4 unsafe to use?

ssl rc4

### Avalanche effect in DES

I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES

encryption block-cipher des feistel-network

### Where can I find examples of ECC implemented in VHDL?

I am looking into implementing ECDSA signature and ECDH key agreement in a Xilinx FPGA. All the examples I have found of VHDL implementations skip over how to construct the low level ECC primitives …

elliptic-curves ecdsa reference-request
 asked by g. garcia 1 vote

### Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?

I know we could possibly be using DH key exchange, that would enable PFS. However, what if we make modifications on our SSL 3.0 handshake such that the only cipher we use is RSA for the achieving PFS? …

rsa diffie-hellman ssl
 asked by Bob White 1 vote

### Has the distributed project "Number Fields @ Home" project benefited cryptography in any meaningful way?

Is there any new understanding, property, or knowledge that has come from the Number Fields @Home distributed computing project? Has any outcome advanced the study of cryptography, or altered …

number-theory