-2
votes
0answers
27 views

Hash Functions and XOR operations [closed]

Alice and Bob want to jointly generate a 512-bit symmetric encryption key. Since neither of them trusts the capability of the other party to generate a secure key, they decide that every bit of the ...
3
votes
2answers
157 views

Reversing DJB2 Hashes

I have some spare time, and a few hundred DJB2-hashed values sitting around. I thought I'd try to do something "useful" and invert DJB2, such that I could calculate the plaintext of the hashes (which ...
1
vote
1answer
114 views

Where do I truncate the bits in SHA 256 hash algorithm?

I'm implementing SHA-256 in PHP using strings. Where do you truncate in the algorithm? There are a lot of places where there's binary addition happening so the number of bits in $W(i)$ keep ...
1
vote
1answer
182 views

Building a stream-cipher out of a hash function?

I've already read this: Is it feasible to build a stream cipher from a cryptographic hash function? However, my proposed construction differs… Suppose the hash generates N bits. These bits are split ...
3
votes
1answer
120 views

Skein state size advantages

Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
2
votes
0answers
179 views

implementing a cryptographic hash with a block cipher [duplicate]

How can a cryptographic hash function be implemented/created using the block cipher? I was wondering if we can use AES in cipher block chaining mode to implement it.
1
vote
0answers
132 views

Hash function that is efficient on GPU and poorly suited to ASIC

I have such requirements to the hash function in my project: operating on 32-bit data, not mathematically breakable (built on existing hashes known to be secure), free of branching, as much as ...
4
votes
3answers
221 views

Can insecure algorithms be combined to form a secure algorithm?

This is hypothetical as I can't think of any reason to do this, but out of curiosity... Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite ...
28
votes
1answer
1k views

How is the MD2 hash function S-table constructed from Pi?

For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ...
2
votes
2answers
237 views

Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...
6
votes
1answer
353 views

Is the first version of the Message-Digest algorithm by Ronald Rivest publically available?

Diving into the history and evolution of the Message-Digest algorithm by Ronald Rivest, I have been able to track back papers from MD6 down to MD2. Yet, somehow I can not seem to be able to find any ...
3
votes
1answer
44 views

Distributing blocks with validation and non-dependant list generation

Problem Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
8
votes
7answers
589 views

Turning a cipher into a hashing function

This is theoretical question. I'd like to know if it's possible (and what are eventually the consequences), not that I'm going to do it in one of my projects. ;) The first hashing functions created ...
1
vote
1answer
115 views

Trapdoor implementation

Please refer to this secure index paper. On page#6, a trapdoor is defined as ...
4
votes
5answers
2k views

Are there hash algorithms with variable length output?

I understand that for example MD5 produces a 128 bit hash value from a given text of variable size. My question is if there is a hash-like algorithm that will produce a hash value where one can ...
2
votes
2answers
249 views

Idea for user/pass hashing to prevent rainbow tables, would it work?

I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
6
votes
1answer
112 views

Abstracting primitives and modes of operation

I am developing a symmetric crypto library and have reached a roadblock. Looking at block ciphers, it is quite obvious that all block ciphers are trivially abstractable as a simple primitive ...
3
votes
1answer
481 views

Do Cryptographic Hashing Algorithms operate only on Integers?

Do all the Cryptographic hashing algorithms operate only on integers (32 bit or 64 bit)? Is there any operation performed on Floating Point Numbers as well? The reason I ask this is because I read ...
6
votes
2answers
6k views

Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509

What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"? Edit: I'm creating the ...
9
votes
2answers
3k views

How can I calculate the SHA-256 “midstate”?

Recently I've been trying to implement some Bitcoin-related code, and I've stumbled upon a weird concept, a SHA-256 "midstate". Some explanation is given here. The general concept is that Bitcoin ...
9
votes
3answers
568 views

Counter mode secure hash algorithm

Ever since the SHA-3 competition, I've been wondering if it is possible to create a hash algorithm that is easier to parallelize. The current algorithms all seem to require building a tree of hashes. ...
4
votes
3answers
2k views

How can I create a fixed length output in my hash function?

I've been recently looking into the creation (and theory) of hash functions, however I just can't figure out how to turn a message into something of a fixed length. At the moment, my theory of a hash ...
16
votes
2answers
5k views

Why use an Initialization Vector (IV)?

Why use an Initialization Vector (IV)? How are IV's used? What are the advantages/disadvantages of using an IV? Why use an IV instead of a longer key in which some section of the key is pubic? What ...