# All Questions

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### SSTP MSCHAP-V2 Authentication before SSL or after SSL Session

So with the recent news that there's a lovely new tool to crack MSChapV2 packets. So the question I have is on a SSTP Connection is the MSChapv2 handshake encrypted pre SSL setup or post. Obviously ...
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### Why do we need extra hashing if we could use simpler scheme?

Lets say that we use init vector IV, key K and HMAC key H. Message is M. Mode of operation is CBC !!! We usually encrypt this way: ...
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### What is the name of this kind of protocol

There is a communication protocol that I believe creates the equivalent of a one time pad, with the downside that the secret message must be transferred multiple times. The protocol is so simple that ...
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### Are there any multiparty homomorphic encryption schemes?

Are there any multiparty homomorphic encryption schemes ? Most of the literature is about two party schemes . Is there any generalization made for n party ?
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### What would be the most effective way to brute force a 16 char AES key?

I have a file that is encrypted in AES using a 16 char string. The string is (a-zA-Z0-9) and .,?!. Also, it only contains words ...
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### How do I calculate CRC32 mathematically? [closed]

I want to calcuate the CRC32 algorithm using polynomials directly but I don't know how. I found the generating polynomial listed here https://en.wikipedia.org/wiki/Cyclic_redundancy_check. This ...
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### Why does ROT13 provide no cryptographic security?

I can understand that ROT13 is not secure for obvious reasons, but I'm looking for the theoretical answer. Wikipedia says "The algorithm provides no cryptographic security.." What does it mean to ...
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### Should I use md5 for my new application?

MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application? I don't think so, but I can't seem to convince anyone else that this is ...
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### AES GCM symmetric encryption of data at rest in c#, ciphertext much longer than plaintext

I've written encryption/decryption routines using AES GCM. Code can be found here. I recently realized that the cipher text is longer than I believe it should be. It should add the tag and IV onto ...
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### Is just a bit of random, “fully random”?

I understand that hashing a datetime is a pseudo-random number, and not good in a security context. But what about hashing a datetime plus a truly-random but constant string (just a string that an "...
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### Adaptive Hash Functions: How to tell how many iterations were used?

If an adaptive hash function like bcrypt or PBKDF2 is used in hashing passwords, the number of iterations used in the hashing process can be configured. For a penetration tester or a malicious hacker,...
1k views

### Purpose of outer key in HMAC

From what I know, the HMAC constructions has two strength: It's resistant to length extensions Since the key is consumed before the message, the attacker does not know the initial state, preventing ...
1k views

### Are mouse movement coordinates useful as a seed for a RNG?

Is it good to use a mouse movement as a 64-bit random seed for a Pseudorandom Generator like AES in Counter Mode? Should I only need to get the X and Y coordinates of the mouse movement?
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### Cryptographical formalization of computational privacy

Yesteryears problems of communication privacy has been well defined in cryptography through Asymmetric cryptography. Due to rise in Cloud computational model , computational heavy tasks are being ...
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### Pseudo preimage for a hash made from a cipher

Consider the Miyaguchi–Preneel construction: $H_0 = E(0,m_0) \oplus m_0$ (0 here means a vector filled with zeros) $H_1 = E(H_0,m_1) \oplus H_0 \oplus m_1$ where $E(K,M)$ is a block cipher (for ...
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### Is there a way to break this encryption?

I was wondering about making up a simple system to encrypt a file: ...
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### Can I build a secure tweakable block cipher from a normal one by adding key and tweak?

Let (E,D) be a secure block cipher. Consider the following tweakable block cipher: ...
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### Generating a cryptographically secure, many-time use, symmetric encryption key

I need to generate a 256 bit encryption key described by the adjectives in the title. Currently I intend to create the key using this RNG. Is this a secure manner of creating the key, given that it ...
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### Trying to find an algorithm to share portions of a key with multiple people

Sorry if this question's a bit basic, but I don't know of any way to ask it concisely enough for a search... What I'm looking for is a proven means of doing the following: Create x number of ...
870 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 ...
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### McEliece Cryptosystem Implementations [on hold]

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 ...
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### Recovering state of modified RC4 key scheduling algorithm

Consider this algorithm: ...
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### Can I jettison MAC if I already have SHA1(M)?

I'm currently using SSL with AES-CBC and HMAC for a file transfer containing string M. Now suppose Alice already knows SHA1(M) (and the adversary does not), and she downloads M from Bob using only ...
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### 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 ...
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A "normal", brute-force attack on a cryptographic hashing algorithm $H$ should have a complexity of about $2^{n}$ for a hash algorithm with an output length of $n$ bits. That means it takes about $2^{... 3answers 439 views ### Why is a MAC needed? I agree that for certain encryption systems or modes of operation, a MAC is indispensible. The best example are probably stream ciphers (and therefore also block ciphers in OFB or CTR mode) that ... 1answer 780 views ### Deniability of OTR messaging I've been looking at the off-the-record messaging protocol, and there is something about its deniability property that seems strange to me. Consider the following scenario: In the course of an ... 4answers 1k views ### Signature and Timestamp for Long Term Document Archival Question I have a PDF document intended for long-term (many years, maybe decades) archival which I would like to digitally sign with my personal certificate to ensure its integrity. As far as I understand, I ... 2answers 510 views ### Can a “pattern” in a series of passwords be detected from their hashes (and maybe a single raw password)? Let's say I'm a lazy user of a system with annoyingly frequent password change policies. I may have a "good" password I used initially that is only used for this system but since I have to change it ... 1answer 564 views ### Several questions about Paillier cryptosystem I have several questions concerning the original Paillier cryptosystem as described in Paillier, Pascal (1999). "Public-Key Cryptosystems Based on Composite Degree Residuosity Classes". EUROCRYPT. ... 2answers 347 views ### Relation between Threshold Cryptosystem and Secure Multiparty Computation ? Is there any relation between secure multiparty computation and threshold cryptosystem ? 3answers 2k views ### Is this a secure implementation of password reset email? I am redesigning a password reset email mechanism because the existing implementation scares the hell out of me. My goal is to generate reset codes that are: Expired Tamper Resistant Single Use ... 1answer 459 views ### Is truncating a hashed private key with SHA-1 safe to use as the symmetric key for AES for data at rest? I realize this is mixing the purposes between asymmetric and symmetric crypto, but I was wondering if it is safe to use a hashed, truncated private key (asymmetric) as the symmetric key for encrypting ... 0answers 362 views ### How to properly format a PGP Message Block? As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ... 1answer 560 views ### Is there difference between Algebraic Homomorphic Encryption and Fully Homomorphic Encryption Schemes? Is there difference between Algebraic Homomorphic Encryption and Fully Homomorphic Encryption Schemes? 2answers 368 views ### Is there any recent cryptographic algorithm especially designed for low-level processors? Most modern algorithms require relatively large amount of resources. Is there any recent (and freely usable) encryption/decryption algorithm which is specially designed for low-level microcontrollers ... 1answer 1k views ### How to securely use Elgamal encryption in libgcrypt? How secure is libgcrypt's Elgamal implementation of encryption (how different it is from textbook Elgamal), and how can I tweak padding and other preprocessing actions? For example, I know that usign ... 3answers 2k views ### Why should the RSA private exponent have the same size as the modulus? Consider the generation of an RSA key pair with a given modulus size$n$and a known, small public exponent$e$(typically$e = 3$or$e = 65537\$). A common method is to generate two random primes ...
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I would like to know how to extract contents of the password protected WinRar file without the password. I have downloaded that WinRar file from a file hosting website and found out that it was ...
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### Are there any papers explaining how to port textbook RSA to realworld RSA?

Are there any papers, books, or link where it explains how the plain vanilla "textbook RSA" is actually implemented in practice with all the padding and stuff? Basically, I would like to know the ...
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### What kind of multiparty computation is this?

The classic multiparty computation protocols are defined around " Untrusted parties trying to compute something together". But is there a cryptographic abstraction for, "Trusted parties trying to ...
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### Using same keypair for Diffie-Hellman and signing

Are there any security risks using a single key-pair for both key-exchange and signing? I'm mainly interested in using Curve25519 for key-exchange and Ed25519 for signing. But similar combinations, ...
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### Other than brute force, are there any attacks on Threefish-512 using only a single known plaintext block?

As per title, other than brute force, are there any attacks on Threefish-512 using only a single plaintext block? Are there any attacks like this in any other cipher?
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### PRNG taking advantage of very large seed

Can anyone suggest a good (CS)PRNG algorithm that takes advantage of having a very large (ideally arbitrarily large) seed? I'd like to use several kilobytes, perhaps several hundred kilobytes, of ...
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### Is bcrypt better than GnupPG's iterated+salted hashing method?

GnuPG has slow hash built-in in form of iterated+salted S2K. Does it have disadvantages in comparance with bcrypt or scrypt? Is GnuPG's slow hash method easily automated in GPUs?
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### Is MAC better than digital signature?

MACs differ from digital signatures in the sense that MAC values are both generated and verified using a shares secret key. Does this in any way put MAC on a disadvantage as compared to digital ...
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### Conforming Randomness To An Alphabet

Imagine that we're trying to create a function to generate a random string conforming to a user-supplied alphabet. That way, users can generate random strings with given characters. Something like: <...
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### Using “Additional Authenticated Data” as a secondary key

In implementing a cipher in GCM or CCM mode, you are provided the option to add "Additional Authenticated Data" (AAD). This AAD is required for decrypting the cipher text, and seems to be used when ...