Cryptography Weekly Newsletter

Cryptography newsletter

Top new questions this week:

Does Curve25519 only provide 112 bit security?

In a recent mail on the IETF CFRG mailing list it was claimed that: The (currently missing) security considerations (or somewhere) should describe why Curve25519 is ok when used in contexts where ...

cryptanalysis elliptic-curves  
asked by SEJPM 7 votes
answered by poncho 12 votes

How feasible would it be to generate 300 million public key pairs in 8 hours?

Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time. What would be required in terms of ...

public-key random-number-generator entropy  
asked by Huckle 7 votes
answered by fgrieu 10 votes

What is stopping someone from saving encrypted info, and decoding it later?

When I send encrypted data to a website, using public key encryption, what is stopping someone who is listening from storing my encrypted data, and decryption it in a few years after they have ...

encryption public-key tls  
asked by jabeoogie 6 votes
answered by mephisto 3 votes

Can RSA be securely used for "blind decryption"?

Assume we have the following setup: A client with trusted storage and computing capabilities (e.g. a smartcard) A server with trusted computing and short-term storage capabilities (e.g. RAM + CPU, ...

rsa chosen-ciphertext-attack protocol-analysis  
asked by SEJPM 6 votes
answered by Ilmari Karonen 2 votes

What was the NSA's reasoning for making their bitwise combination functions in SHA-1 the way they did?

I know that these functions are there to actually make the program work. What I want to know is why they made the functions one way but not another. For example, why did they pick F1(B, C, D) = (B ...

hash algorithm-design reference-request sha-1 nsa  
asked by BonBon 5 votes
answered by otus 7 votes

Can iterated hashing be used to mitigate collision and preimage weaknesses?

How much security does double hashing add regarding collisions and preimages? Is it helpful to iterate a hash function even more times than two? For example, can MD5 be fixed (in practice) by ...

hash collision-resistance attack preimage-resistance  
asked by boot4life 4 votes
answered by fgrieu 5 votes

Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?

Imagine we have $t-1$ shares in $(t,n)$ shamir secret sharing. So at least $t$ shares are needed. Question: Why cannot we use $t-1$ shares to find a root of the polynomial and then recover the ...

cryptanalysis secret-sharing shamir-secret-sharing  
asked by user13676 4 votes
answered by mikeazo 4 votes

Greatest hits from previous weeks:

Can you help me understand what a cryptographic "salt" is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...

encryption hash passwords salt password-based-encryption  
asked by Bhavik Ambani 23 votes
answered by MartinSuecia 48 votes

What is safer: ZipCrypto or AES-256?

Like in title: which one of these encryption methods (ZipCrypto, AES-256) is more secure and why? I am asking about it because I'd like to know which should be preferred when compressing files with ...

aes file-encryption compression  
asked by alex 19 votes
answered by mikeazo 20 votes

Can you answer these?

Safe generation of $k$ points on a curve such that the mutual discrete logs are hard?

I have a multiplicative group $G$ of prime order $p$ implemented using a twisted Edwards curve (similar to Ed25519). I want to compute a set of $k$ distinct points $P_1,...,P_k$ that generate $G$, ...

asked by Chris 2 votes

Is there an existing AE protocol with forward secrecy for embedded devices?

I'm working on an embedded device that is connected to a computer over an untrusted channel. According to my threat model I need authentication and encryption on the wire with perfect forward secrecy. ...

protocol-design authenticated-encryption forward-secrecy embedded  
asked by Shnatsel 1 vote

Ciphertext size of any CPA-secure public-key encryption scheme

I know that, for any CPA-secure public-key encryption scheme, the size of the ciphertext after encrypting a single bit is superlogarithmic in the security parameter. That is, for $(pk,sk) \leftarrow ...

public-key chosen-plaintext-attack  
asked by pa5h1nh0 1 vote
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