# All Questions

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### Is it safe to derive a password from a signature provided by ssh-agent?

I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of ...
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### Is Cramer-Shoup backdoorable?

We recently had the question whether it's possible to have multiple private keys with one public key for the cramer-shoup cryptosystem. There it was stated that finding such "secondary" private keys ...
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### Need help with modular inverse of a solution matrix for the Hill Cipher

I've been trying to teach myself the Hill Cipher (and the bit of modular arithmetic that accompanies it) but I can't seem to make it work. Key matrix:  \begin{matrix} 1 & 4 \\ 9 & 16\\ ...
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### What is the original SKID3 protocol?

While searching for a mutual authentication protocol I often stumbled upon SKID3. However I encoutered different variations of it. The basic structure is the following: (1) A --> B: rA (2) B --> A: ...
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### Extension of a password hashing algorithm

I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it ...
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### DSA: Authentication and assurance of authorized parties

When dealing with Asymmetric cryptographic algorithms, usually the sender of the critical data asks the listener for a Public Key for encrypting the data and sending them. This is while the private ...
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### Can a tree hash with leaf-size of 1 byte support verification of content with elided ranges, at a cost of at most 2 supplied internal-node hashes?

Perhaps someone can confirm my intuition: A tree hash with leaves of size 1 (for example Blake2 in a tree-hash mode) would of course not be very efficient. But it seems that it might be a suitable ...
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### Authentication using AES

I need to implement an authentication mechanism in an embedded environment which does not support floating point operations but has an AES accelerator module which allows for encyption/decryption ...
608 views

### How to build an electro-mechanical public key cipher machine?

It is generally assumed that asymmetric encryption schemes were invented in 1973 at GCHQ in Britain and, independently, in 1976 at the MIT. Imagine, if the abstract idea of having a public key and a ...
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### What is ε in differential privacy?

In ε-differential privacy, what does the ε refer to? Is it privacy value or the notation used? Can anyone provide an example of differential privacy?
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### In SSL and TLS, why is there a separate Change Cipher Spec Protocol rather than including a change_cipher_spec message in the Handshake Protocol?

In SSL and TLS, why is there a separate Change Cipher Spec Protocol rather than including a change_cipher_spec message in the Handshake Protocol?
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### Why is the definition of Special-honest verifier zero-knowledge probabilistic?

Let $P$ be a prover willing to prove to a verifier $V$ that he knows a witness $w$ satisfying $(x,w) \in R$ for some relation $R$ and some common input $x$. As found in the literature, $P$ can use a ...
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### How to reconstruct hash value to the original format? [duplicate]

I would like to know how I can reconstruct a hash value such as 558f68181d2b0c9d57d41ce7aa36b71d9 to its original format (734). I have used a code in matlab, which provided me with an hash output, ...
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### Enterprise message bus encryption [migrated]

I'm contemplating using Amazon's Simple Queue System as the basis of an enterprise message bus. According to Amazon, the contents are not encrypted, which means the application(s) will have to handle ...
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### How to use /dev/urandom with PHP to get CS random numbers [migrated]

I need to create random integers between the values of 0 and 10,000,000, and I will need several million such numbers. The numbers must be as close to a CSPRNG as possible in that should (for example) ...
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### MDC-2 recommended IV values?

I'm currently reading Menezes' "Handbook of Applied Cryptography", and in it, when describing the MDC-2 cryptographic hash function, has the following line: Choose the 64-bit non-secret constants ...
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### AES storing the length within the encrypted data versus storing it outside

I need to strip off padding after decrypting AES(CBC)-encrypted data (I have control over encryption and data transmission), so have looked at adding the length of the original data to the payload ...
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### LUKS multiple key slots - what's the intuition?

LUKS volumes have the ability to allow multiple independently usable passwords, as explained here: [https://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions] The intuition behind basic ...
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### Is there a secure source of entropy on a typical microcontroller?

On a device that does not have a hardware RNG, what is the best source for entropy? Some options and pitfalls floating around: Use the ADC to read something analog: can become deterministic if ...
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### RSA signature attack check on lowest 16 bytes - Implementation

I am referring to solution given in this question I need help to implement Poncho hint in this comment: As the first question i have an RSA signature of 1024 bit applied on an hash (MD5) of the ...
44 views

### More efficient and just as secure to sign message hash using Ed25519?

According to the Ed25519 paper, the (potentially long) input message is hashed twice (see Section 4 page 12 steps 1 and 3). This webpage has a nice diagram toward the bottom that illustrates this, ...
582 views

### A block cipher with independent keys for each round

I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ? Thank you. EDIT Some missing ...
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### How does one launch a CPA2/CCA2? [on hold]

There is a (very small) game I play that stores password entries into the local regisry. The entries in the registry form 49-character strings (1 + 32char cipher + 16 constant trailing characters). ...
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs ...