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1500 questions
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4 answers

Can one generalize the Diffie-Hellman key exchange to three or more parties?

Does anyone know how to do a Diffie-Hellman or ECDH key exchange with more than two parties? I know how to do a key exchange between 2 parties, but I need to be able to have a key agreement between 3 or more parties.
hobeau
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Is there a secure cryptosystem that can be performed mentally?

I, myself, do not plan on getting into a situation where I would be unable to use a computer in order to communicate securely. However, I can think of many practical situations in which mental cryptography would be useful. Is there a secure…
John Gietzen
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How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ?

I have read in Applied Cryptography that the NSA is the largest hardware buyer and the largest mathematician employer in the world. How can we reason about the symmetric ciphers cryptanalysis capabilities of code-breaking agencies like the NSA or…
jokoon
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1 answer

Why use argon2i or argon2d if argon2id exists?

I am currently working on a project where I want to implement Argon2. The problem is that I dont really know a lot about it. Internet research is not really helpful, because Argon2 is only 2 years old so all that really exists are scientific papers…
Richard R. Matthews
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46
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3 answers

What are the differences Between “White-Box Cryptography” and “Code Obfuscation”?

I have been reading the question "What is a white-box implementation of a cryptographic algorithm?" and it led to this short article / Q&A which states in question 2: Q2: What is the difference with code obfuscation? Related and complementary…
MByD
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46
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3 answers

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy of my users, I think this should be one of the…
user34484
46
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1 answer

What is a "freestart collision"?

In their work on SHA-1 collisions (cf. the EUROCRYPT-2016 paper “Freestart collision on full SHA-1” by Stevens, Karpman, and Peyrin) Stevens et al show that they are able to generate "freestart collisions" on SHA-1. They say: Even though freestart…
otus
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2 answers

Is Triple DES still considered safe to use?

What it says on the tin. Is it still used in things like TLS?
Melab
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45
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2 answers

What do the magic numbers 0x5c and 0x36 in the opad/ipad calc in HMAC do?

Wikipedia lists the following pseudocode for HMAC: function hmac (key, message) if (length(key) > blocksize) then key = hash(key) // keys longer than blocksize are shortened end if if (length(key) < blocksize) then //…
sneak
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44
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7 answers

For a hashing function like MD5, how similar can two plaintext strings be and still generate the same hash?

When I say similar, I'm referring to the Hamming distance, the Levenshtein distance, or a similar string distance metric that measures how similar or dissimilar two strings are. For instance, are there two plaintext strings with a Levenshtein…
John Ellmore
44
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2 answers

AES-GCM recommended IV size: Why 12 bytes?

When using AES-GCM, a 96-bit IV is generally recommended. Most implementations I've seen also use 96-bit. However, I'm unsure on where this recommendation or convention comes from. Let's assume a shorter IV is bad. Assuming all other constraints for…
Hendrikvh
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44
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2 answers

What's the fundamental difference between Diffie-Hellman and RSA?

What is the difference in the purpose of DH and RSA? Aren't they both public-key encryption?
user541686
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44
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5 answers

What is the SSL private key file format?

I was researching about how to encrypt with RSA. I understood everything but not the format of the private keys. In the phpseclib (RSA in PHP), you can import your private key (private.key format) and in the key file there is text like…
tor
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Can I remove newlines in a public key?

Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or AAA\n\rBBB\n\rCCC\n\r is this the same as AAABBBCCC
xpepermint
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6 answers

Does RSA work for any message M?

I decided to read the original RSA paper A Method for Obtaining Digital Signatures and Public-Key Cryptosystem because of a question I had about RSA (which is not the question I'm about to ask, but may be a question on here at some time) and came…
mikeazo
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