# Tag Info

### Cryptography algorithms that take longer to solve on a GPU than a CPU

This specific situation is a central part of the analysis of password hashing functions. Indeed, for hashing a password, we want a function which is: slow in a tunable way; such that the most cost-...
• 87.4k
Accepted

### What are recommended, general strategies to start block-cipher design and/or analysis?

In order to design and analyze a cipher, we have to establish what a cipher is supposed to accomplish. Put simply, we would like to be able to transform information in such a way that only those who ...
• 19.7k
Accepted

### How are the functions used in cryptographic hash functions chosen?

The functions considered are binary functions of 3 bits to 1 bit (extended to bit vectors, that is bitwise functions). There are $2^{(2^3)}=256$ such functions. All the functions considered are ...
• 143k

### Why is this not a viable key exchange algorithm?

I've simplified the Alice random bytes to ARB and Bob random bytes to BRB. Then the protocol follows as; Alice knows $key$ and $ARB$ and sends $$C_1 = key \oplus ARB$$ Bob knows $C_1$ and $BRB$ and ...
• 49.1k
Accepted

### Creating cryptographic algorithms at runtime

This doesn't add new security as much as it just shifts it. Encryption algorithms are carefully studied. Hmm... I didn't make that emphatic enough. Encryption algorithms are C A R E F U L L Y ...
• 3,271
Accepted

### Is it possible for a cryptographic algorithm to limit the number of times a package/ciphertext can be decrypted?

Cryptography itself cannot solve this problem. This problem has long been studied in the field of copyright management to prevent piracy. The main issue is that it is difficult to keep a state in the ...
• 4,188
Accepted

### Do identical strings always have the same SHA-256 value?

Yes, if you hash the same input with the same function, you will always get the same result. This follows from the fact that it is a hash-function. By definition a function is a relation between a ...
• 6,966

### What are recommended, general strategies to start block-cipher design and/or analysis?

There is no such thing as a clearly defined, unambiguous, optimal learning path. However, drawing from my own experience, I would suggest tackling the following in due sequence: Linear cryptanalysis: ...
• 87.4k

### If Kerckhoff's Principle holds, why do we need a cipher at all?

...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search ...
• 19.7k
Accepted

### Theoretically, what if I were to change some magic numbers in, say, AES?

How are these (magic) numbers chosen? It heavily depends on what algorithm and which of its magic numbers. They seldom are entirely arbitrary. In AES, it is often taken the lowest value such that a ...
• 143k
Accepted

### Are there any (asymmetric) cryptographic primitives not relying on arithmetic over prime fields and/or finite fields?

Braid cryptography? Knapsack cryptosystems, like Nasako–Murikami? Lattice-based cryptography tends to work in polynomial rings or modules with coefficients in finite fields, but whose higher-level ...
• 48.8k
Accepted

### What can make an implementation of a large integer library unsafe for cryptography

Some large integer libraries can be unsafe to use for writing cryptographic algorithms Yes. Leaving aside plain bugs (buffer overflows, incorrect result in edge cases), there is the issue of side ...
• 143k
Accepted

• 22.9k

### What is the difference between SHA-3(Keccak) and previous generation SHA algorithms?

They are all hash functions. Apart from that, they are structurally quite different. The SHA family (SHA-0, SHA-1, and the SHA-2 functions such as SHA-256 and SHA-512) use the Merkle-Damgård ...
• 87.4k

### Calculation-Intensive Decryption

You could throw away bits of the encryption key so that there is a brute-force portion to decrypting e.g. encrypt with a 128-bit key but only share 96 bits. Or protect the key using something like an ...
• 2,627