Implementing a cipher or protocol is the process of taking it from its mathematical or algorithmic description and producing a working version, often in computer software or hardware. This tag should be used for any question discussing the various potential considerations and pitfalls of this ...
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Reverse engineering a hash?
I understand this may not be the best place to ask a question like this, but I believe that this community may be the best/only place I can ask such a question.
I have inputs and outputs from an ...
10
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3answers
897 views
Known methods for constant time (table-free) AES implementation using 'standard' operations?
There are several known methods for implementing AES in constant time using SIMD operations, mostly based around fast byte shuffling (for instance Hamburg and Kasper/Schwabe). Are there any similar ...
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What is a white-box implementation of a cryptographic algorithm?
What is a white-box implementation?
Does a white-box implementation have specific properties?
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Types of Cryptography for a 4-8 bit microcontroller
This is more of a research question.
I was wondering what types of crypto algorithms would work best on a small 4-8 bit micro controller. I recently read a paper called Security Considerations for ...
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3answers
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How can a random salt for a hash function work in practice?
I understand the theory behind the use salts in hash functions, but when I see it implemented, the implementations always generate the salt on the fly and the salt appears to be different for every ...
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4answers
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Can I determine if a user has the wrong symmetric encryption key?
We're using the Objectivity/DB object database with a custom encryption plugin that encrypts serialized objects on disk. Encryption uses AES with a shared secret key held by all users. I would like to ...
7
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2answers
549 views
How should I store passwords that need to be available in plain text?
Suppose I need to store login information for a third-party website for a few users, how would I go about doing it?
Since I am logging into a third party website, I need the password in plain-text, ...
6
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2answers
498 views
Can one implement AES on 4-bit microcontroller?
It is possible to implement AES on 4-bit microcontroller? As far as I know, AES on 8-bit microcontroller are common especially for light weight application such as the RFID.
I have yet to come across ...
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2answers
192 views
Unit testing a library RNG and its seeding for practical security
Suppose I have a cryptography library that provides me with a black-box random number generator that is supposed to be suitable for long-lived key generation. (Under the hood it may be assumed to use ...
6
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1answer
439 views
Implementation of Tao Xie and Denguo Feng's MD5 attack
It is well known that MD5 is completely broken today - however, to understand the theory behind the attacks I am looking for an implementation of the collision attacks described in the 2009 paper A ...
5
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3answers
464 views
How can my application make sure the right symmetric key is used for decryption?
I am developing an Encryption/Decryption Utility using Adobe AIR. I have chosen the AES algorithm and currently use the as3crypto library for this. My query is in ...
5
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1answer
276 views
Are there any MGF1 and OS2IP functions available in C?
I need MGF1 and OS2IP functions, as defined in the PKCS #1 v2.1: RSA Cryptography Standard.
Is there anything available in OpenSSL, or any other open C library?
5
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1answer
311 views
What is the proper way to use a client nonce?
I've implemented an API for one of my clients, it relies on nonces and a shared secret. The structure:
Client's Site (CS) requests nonce from My App (MA), posting their username
MA verifies the ...
5
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1answer
192 views
Are there any Implementations of Secure Indexes?
There are several papers about Secure Indexes, for Example "Searchable Symmetric Encryption:
Improved Definitions and Efficient Constructions" and "Secure Indexes". ...
5
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3answers
1k views
Is there any opensource white-box implementation of AES or DES?
I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided.
The same page also links various papers about ...
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2answers
174 views
Signature schemes for underpowered devices (8bit microcontroller)
I am currently researching into a small scale home automation system, aiming for cost. The system architecture is basically one master and several slaves which are connected in parallel.
Recently ...
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3answers
225 views
McEliece Cryptosystem Implementations
Are there any current implementations (language irrelevant) of the McEliece Cryptosystem?
I have been hunting around all day, and yet, have only found a few mathematical equations pertaining to the ...
4
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1answer
214 views
Why x00 is usually avoided in salt?
In .NET Framework, there is a cryptographic Random Number Generator (RNG) provider which enables to generate a cryptographically strong sequence of random bytes. This provider contain, among others, ...
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1answer
81 views
Two way encryption with random IV
I'm attempting to encrypt some information into our database to be later pulled back out and displayed to the user. Searching and reading up on different methods I found a post over at stack exchanged ...
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2answers
318 views
Is this a correctly formatted PGP session key packet?
RFC 4880 may be full of information, but it can be incredibly vague at times, so im looking for someone who actually knows the answer to this.
Given this public key:
...
4
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5answers
461 views
Software implementation of a commutative cipher?
I've got an application (detailed below) that calls for the use of a cipher that is commutative. I've been doing some googling & reading, and there are two algorithms that seem to get mentioned ...
4
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1answer
190 views
Length of data to hash for PGP
I have finally managed to verify some simple PGP signed message blocks. However, I discovered that for some reason, my implementation limits me to verifying data that is 9-16 bytes long. no less. no ...
4
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3answers
279 views
Order of cascaded ciphers
Does the order of a block cipher cascade (e.g. in TrueCrypt) make a difference to the security provided, assuming independant keys?
For example:
...
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3answers
302 views
How can I avoid calculating with huge numbers when implementing the RSA algorithm
There is 26-letter English alphabet.
There is the plain text: TRYAGAINLATER.
I need to encrypt it by RSA algorithm with the public key 53.
What is the ciphertext?
...
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3answers
222 views
How to avoid a chicken and egg scenario with encrypting passwords?
I am working on application that allows users to upload files containing company data and then share those files with a list of other users that have specific roles within the system.
I want to ...
3
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2answers
357 views
Implementing AES in C++: 4x4 Array of unint8_t, or 4x1 array of uint32_t?
I'm implementing AES in C++, and, inspired by the way words are handled in SHA, I decided this time to handle the state as a one dimensional array of 4byte unsigned integers as opposed to a two ...
3
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1answer
171 views
Does omitting the first two lines of RC4's pseudorandom generation algorithm weaken the cipher?
A particular educational software program published by a U.S. government agency uses a variant of RC4 to obfuscate its data files (see Stack Overflow question). The variant of RC4 in question is ...
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2answers
297 views
How does one calculate the cryptoperiod?
NIST Special Publication 800-57 defines a cryptoperiod as
the time span during which a specific key is authorized for use by legitimate entities, or the keys for a given system will remain in ...
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1answer
238 views
What is the computational cost of a public key certificate signature verification?
What is the computational cost of a certificate signature verification in terms of exponentiation, multiplication and other computation operations?
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2answers
571 views
How key materials are generated in SSL V3 from master secret
The generation of key materials is given by
...
3
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1answer
237 views
On-the-fly computation of AES Round Keys for decryption?
The usual implementation of AES first computes all the Round Keys sequentially starting from the key, and stores them in RAM for later uses. However, when enciphering a single block with a key that ...
3
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1answer
651 views
What is the 'Version Incompatibility" Problem in TLS 1.1/1.2 and 1.0?
It's unclear to me if there are multiple problems, or a single one, (and just what that problem is) with servers incorrectly negotiating down from a client offering 1.1 or 1.2 to something they ...
3
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1answer
183 views
Undecrypt using the OpenSSL EVP API?
I'm writing a client-server encryption scheme for homework, and I've stumbled upon what might be a fatal blow to my current implementation.
When using AES-256-CBC on the two sides, it's important ...
3
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1answer
209 views
Best choice of finite field for AES on a 4-bit microcontroller?
As the finite field of $GF(2^8)$ are isomorphic to $GF((2^4)^2)$, $GF((2^2)^4)$ and $GF(((2^2)^2)^2)$,
which of the fields is best suited and most efficient for 4-bit MCU and why? Would it be ...
3
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1answer
165 views
How does the energy consumption of the SHA-3 finalists compare?
I am curious, is there any paper where SHA-3 competitors are compared in terms of energy efficient?
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2answers
170 views
Cryptographic GUID?
I need a GUID. Really just any number that is likely to be unique. However I prefer not to leak time and other things as a GUID may leak. What should i use as a cryptographic replacement? I was ...
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2answers
219 views
Additive ElGamal cryptosystem using a finite field
I'm trying to implement a modified version of the ElGamal cryptosystem as specified by Cramer et al. in "A secure and optimally efficient multi-authority election scheme", which possesses additive ...
2
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1answer
71 views
Rapidly changing passwords?
Suppose you need to authenticate yourself to a program with the password - but the program's source code is public, the program doesn't have access to any private information and all your ...
2
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2answers
139 views
MD5 implementation doubt
In MD5, there are four rounds. After every round, why do we need to add the computed Q values to the initial values and then take this value as input to the next round. For example after the first ...
2
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1answer
193 views
Padding for the TEA
Sorry if this is a noob questions, but I finally figured out how to implement the Tiny Encryption Algorithm in C++.
My question is what to do about padding the key and the plaintext? I know that ...
2
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1answer
93 views
How does DJB's nistp224 manage to fit compressed points into 224 bits?
DJB's nistp224 program purports to be an implementation of elliptic curve Diffie-Hellman relative to the standard NIST P-224 elliptic curve.
To the best of my ...
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2answers
796 views
How to distribute session keys in public key cryptography?
In public key cryptography we can also use session keys which are symmetric. How do the sender (say a server) provides this session key information to its clients?
If the sender (here server) ...
2
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1answer
124 views
What should I be aware of when implementing algorithms myself?
I plan to build my own crypto library. The project will be primarily for me to learn (and if useful for no other purpose, that is fine). In the past I have implemented a few hashes, and AES quite a ...
2
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3answers
424 views
Hash function in PBKDF2
From this excellent answer I learned (correct me if I am wrong) that when writing a block cipher with say key size 128 bit, one has to pad the password given (variable size) so that it becomes exactly ...
2
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1answer
284 views
Implementing the BGN Cryptosystem
Question: If you had to implement BGN, how would you do it?
I'm looking for an implementation of the public-key cryptosystem due to Boneh, Goh, and Nissim (aka BGN), or at least some suggestions on ...
2
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1answer
397 views
Format-preserving encryption implementations
I'm looking for a general, free implementation of Format-preserving encryption
as described in this article and on wikipedia.
Possibly in a well established cryptography toolkit.
My intention is to ...
2
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1answer
596 views
AES-NI implementation examples
Newer Intel and AMD processors have hardware support for implementing AES using the instruction set AES-NI (instructions AESENC, AESKEYGENASSIST etc). Do you know of any clean example implementation ...
2
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1answer
306 views
Is there a standard for OpenSSL-interoperable AES encryption?
Many AES-encrypted things (files, strings, database entries, etc.) start with "Salted__" ("U2FsdGVkX1" in base64).
I hear it's some sort of OpenSSL interoperability thing a b c.
Is there some ...
2
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1answer
201 views
Verilog simulation & synthesis of Diffie-Hellman key exchange
Is there any freely available verilog implementaion of Diffie-Hellman key exchange?
I couldn't find anything using google. So, assuming its not there I started implementing on my own.
The code is ...
2
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1answer
291 views
Hash or encryption function for challenge-response protocol?
Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...
