All Questions

141 views

Requirement for the length of a HMAC tag?

I've seen NIST requirements about key length. What about the output lengths ? Is 112 bits enough for the HMAC output length ? Can we truncate the tag to keep only 112 bits ? Thank you
130 views

Building a pad for OTP on-the-fly with Diffie-Hellman

Through repeated DH attempts, could Alice and Bob build a large random key for use as a one-time pad? My intuition is that this protocol would be as hard as breaking DH (discrete logarithm).
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fully homomorphic encryption (FHE)

Please, I would like to find some hints or solution to my following problem, I would appreciate your assistance to walk with me throughout the solution Given fully homomorphic encryption (FHE) ...
262 views

extract ciphertext from encrypted SMIME file

the main question of this message is how to get the true ciphertext from S/MIME file? I created RSA keys and encrypted a message with S/MIME as follow : ...
115 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
217 views

Key derivation for AES-Encryption key and HMAC

Okay so I have two options for how I would derive two keys for AES encryption and HMAC they are as follows: Run BCrypt on a users passphrase and then use the bouncy castle implementation of HKDF in ...
289 views

Blowfish ECB mode: Tools for known-plaintext attack?

I'm currently dealing with multiple blowfish-encrypted files that share the same key. All are encrypted using ECB mode judging from their appearance: I don't know what the key is but I know 64 byte ...
390 views

IPsec authentication and encryption lgorithms

I am looking for the implementation of IPsec security algorithms for both authentication and Encryption. Is there any open source implementation available for the same ? And if someone supposed to ...
98 views

What is the value of Q such that Q|P-1 where P is a prime number?

For my crypto assignment, I'm asked to enter a prime P and generate Q such that Q|P-1 Can anyone guide me what is Q|P-1?
72 views

Is Paillier cryptosystem commutative?

Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier?
169 views

How do I safely anonymize/hash a unique identifier to protect privacy?

I am building a system to collect a unique identifier (MAC addresses from 802.11 probe requests). The system will have several collection points over a large area, submitting to a central database. I ...
79 views

How can a good encryptor be made?

I am making an encryptor software for a stream cipher with my own PRNG as a project for an inter school science competition. How can I make one so that after it generates the pseudo random nos. it can ...
235 views

Crypto libary with Commutative Encryption

I want to implement Mental Poker in JavaScript as a toy program and lead in to a larger serious project so I did my research and found Massey-Omura cryptosystem and the Shamir three-pass protocol ...
326 views

Can public key be recovered from ciphertext & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM. The ...
166 views

Encrypting twice with same key gives back plain text

I read in the answer here that when encrypting twice the plain text with same key could result in plain text as shown below $encrypt_{key}((encrypt_{key}(plain)) = plain$ Which block-cipher ...
365 views

A simple attack on DESX in time $2^{120}$ [duplicate]

Let $\mathcal{M}$ be our message space and $\mathcal{K}$ our key space. Now, let $\mathrm{E} : \mathcal{K} \times \mathcal{M} \to \mathcal{M}$ be a block cipher. Define the block cipher ...
73 views

Are there any many to one encryption frameworks available?

I am reasonably new to the cryptography. For my use-case I need a method where in I would need a receiver to accept encrypted messages from a range of senders (each having their own, say, public key). ...
265 views

Monoalphabetic cipher key

I'm new to cryptography and have just completed homework on Monoalphabetic cipher. I managed to decrypt the cipher text successfully but I cannot identify the key from my plaintext to ciphertext ...
63 views

Where is defined the fact of having a “learning” and “challenge” phase in cryptography proofs?

I've read Bellare and Rogaway 2004 and Shoup 2004 about game-based cryptography proofs, but I lack precisions about how should be built the "learning" and "challenge" phases, since my games will ...
76 views

Can Diffie-Hellman be scaled up or force-multiplied?

I'm not too familiar with the math involved with the exchange of keys, I've read it over several times, but math isn't my strong point. My understanding is that smart people are hard at work to ...
67 views

SpongeWrap without padding and frame bit

Assuming all inputs are same length as rate except last can be shorter. Is it necessary to pad every input (not just last) to sponge for authenticated encryption to be secure? Is this just, because ...
286 views

Using C_Sign to create a PKCS7 signature

I am using the PKCS#11 function C_Sign to sign some data. The output I get is just a signature. How do I get it in PKCS#7 format - i.e. ASN1 with signature and certificate (for detached) or ASN1 with ...
112 views

Block Cipher Modes

I have a question here asking the following: Why do block ciphers need the use of blocking modes? To encrypt messages larger than the size of the block. To avoid having the same block ...
90 views

Breaking RSA moduli

Let suppose that the sizes of factors $p$ and $q$ are $b$ bits. We construct two RSA numbers $n$, $n'$ of same sizes. Can we say that the duration to break these two numbers is two times the duration ...
426 views

What benefits do substitution boxes and permutation boxes offer in DES?

I understand that with more encryption rounds the more complex the ciphertext becomes due to multiple substitutions and permutations. What I don't understand is the purpose of these features. I am ...
212 views

How can I do minus on plaintexts in the Paillier cryptosystem?

We have $E(a)$, $E(b)$ encrypted under the same Paillier key. As we all know, we can get $E(a+b)$ by calculating $E(a)*E(b)$. But can we get $E(a-b)$, by calculating $E(a)/E(b)$? I tried to ...
57 views

What does OIW stand for

There seem to be many OID's that have been put in the ASN.1 tree that have the following ISO identified organization: OIW. One example is SHA-1 (ElGamal seems to be another): ...
173 views

Triple DES in Firefox - in practice

Reading about triple DES and understanding the principles, I am still curious how Firefox defines their three keys for the encryption/decryption. Suppose that the user saves his passwords in the ...
305 views

Message encrypted with a LFSR based stream cipher

I am learning about LFSR sequence and I came across this question: A 16-bit message consists of two ASCII characters. This message was encrypted with a one-time pad, and the key for the one-time pad ...
99 views

Basic question about design of program with data encryption

I need to store encrypted files on a hard disk. The actual code side is not important for me now (I plan to use C# and AES-GCM encryption from Bouncy Castle library, please tell me if you think that's ...
77 views

Deprecation of RSA-SHA-1 in DKIM keys?

I recently noticed that OpenDKIM on my mail server is objecting to DKIM signatures from a client, saying their key is insecure. It may be that that's due to lack of secure DNS (confirmation anyone?) ...
222 views

For calculating the index of coincidence for each sequence

I was learning about the finding the key length reading the following web site... http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ and I really don't ...
201 views

Is it feasible to use combination of ABE schemes for encrypting the data?

I have a peculiar requirement for preserving the shared log files. For example I have 1000 records which belong to different organizations as listed below and all the logs are present in a single CSV ...
93 views

Partial Homomorphic Schemes that are probabilistic

As mentioned in wikipedia there are many Partial Homomorphic Encryption(PHE) scheme like RSA, Elgamal, Pailler etc. Pailler encryption scheme seems to be probabilistic Are there any other PHE ...
170 views

Engima machine decoding with PC and GPU

I saw this answer at this site about decoding a 3-rotor Engima machine's settings: How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint? And did some math for ...
64 views

Verifying signature owner (without verifying the actual document)

Programming in Java. I have an RSA key-pair, a document, and a signature created with the Java Signature class, using SHA512WithRSA. In order to verify the signature, of course, I need to provide the ...
106 views

AES Affine Transformation Polynom Representation

I have been reading on the polynomial representation of the AES Sbox in the PDF “Essential Algebraic Structure Within the AES” by Murphy and Robshaw (www.isg.rhul.ac.uk/~sean/crypto.pdf) on page 7, ...
156 views

How often do I need to rotate AES 256 keys

I'm trying to design a protocol for a resource constrained environment. The device has to communicate with a server through an insecure node. My plan is to use AES 256 end to end for all ...
254 views

How to prove Security of Onion Layers of encryption?

CryptDB has Onion layers of Encryption to provide wider functionality from weaker forms of encryption. How do we prove such things are indeed secure ? Intuitively It seems ok. Are there any parallels ...
460 views

Why is Rijndael key length restricted?

Why is Rijndael restricted to key length in {128, 160, 192, 224, 256} bits (and not larger)? The algorithm looks to me like it would support an arbitrary-sized key (multiple of 32). The rounds ...
152 views

Comparing Difference Distribution Tables

I have been studying the Diff. Cryptanalysis and finding it hard to do a problem. The problem is I have calculated the tables programmatically and found that the second table has a max value of 6 ...
230 views

EAX: OMAC and CMAC

OMAC is specified as the underlying algorithm to provide authentication within the EAX authenticated encryption (with associated data). Would that be OMAC1 or OMAC2? If it is OMAC1, does that mean it ...
248 views

114 views

Does OpenTSA support PKCS11 to talk to HSMs?

We are planning to implement the time-stamping service (RFC 3161) using OpenTSA wanted to know: Does OpenTSA support PKCS-11 (Cryptoki) to talk to HSMs? BTW: I did not find documentation or much ...