Cryptography Weekly Newsletter

Cryptography newsletter

Top new questions this week:

Why do stream ciphers use a nonce?

My question maybe will be stupid, but my problem is that I do not understand why stream ciphers need a key and also a nonce. As far as I understand, the keystream is generated with the nonce. The same ...

stream-cipher nonce  
asked by franz1 8 votes
answered by fgrieu 12 votes

Why is PuTTYgen-created RSA public exponent(e) not in {3,17,65537}?

As far as I know, RSA public exponent(e) should be one of {3,17,65537}. However, I found PuTTYgen-created RSA public exponent(e) is 0x25(37) by default,as follows, (PuTTYgen version: 0.66) I am ...

encryption rsa public-key  
asked by Matt Elson 6 votes
answered by fgrieu 12 votes

Simulation-based proofs and universal composability proofs

I recently read Ran Canetti's famous UC paper but I'm still trying to wrap my head around the concepts. I think this answer has me confused a bit, particularly where it says The stand-alone ...

provable-security zero-knowledge-proofs protocol-analysis universal-composability  
asked by Luke 6 votes
answered by Mikero 4 votes

argon2 versus bcrypt/PBKDF2 password hashing security gain

I wonder if it can be approximated how much of a security margin the new argon2 hash, winner of the password hashing competition, can give over bcrypt or PBKDF2, for an attacker using large GPU ...

hash key-derivation pbkdf argon2  
asked by azenz 5 votes
answered by Stephen Touset 2 votes

Brute force attack multiple stream cipher

Assume that a scheme used to secure a specific system $Π=(Gen,Enc,Dec)$ which is thought have indistinguishable multiple encryption in the presence of an eavesdropper. For any adversary $A$ that can ...

provable-security stream-cipher brute-force-attack  
asked by M.S.B 4 votes

Is there any reason not to use EdDSA with Weierstrass curves?

I'm volunterely working for a crypto library and we're planning on adding Curve25519 support (finally). At the same point I had the idea of adding support for EdDSA in the same run. Our library is ...

elliptic-curves dsa ed25519  
asked by SEJPM 3 votes
answered by Ruggero 1 vote

What followed findings of A. Lenstra et al. concerning shared factors of practical RSA moduli?

A. Lenstra et al. had a paper in 2012 "Ron was wrong, Whit is right", in which one reads: "What surprised us most is that many thousands of 1024-bit RSA moduli, including thousands that are contained ...

asked by Mok-Kong Shen 3 votes

Greatest hits from previous weeks:

If you hashed a hash an infinite number of times would you end up with a unique hash?

If you took a hashing algorithm for example MD5 and repeatedly passed the output hash back into the algorithm an arbitrarily large number of times would you eventually end up with one unique hash? My ...

hash entropy  
asked by Alex Lewis 12 votes
answered by Thomas Pornin 31 votes

How secure is AES-256?

The cipher AES-256 is used among other places in TSL/SSL across the Internet. It's considered among the top ciphers. In theory it's not crackable since the combinations of keys are massive. Although ...

encryption tls aes  
asked by Gustav 19 votes
answered by erickson 17 votes

Can you answer these?

What's the perfect chain length : number of chains ratio for rainbow tables?

I'm building a SHA-1 rainbow table to crack basic passwords (i.e. up to 10 character, 0-9,a-z). But I can't seem to calculate that golden ratio that would give me the most coverage. Also is there ...

sha-1 rainbow-table  
asked by nappyboi 2 votes

Does CP-ABE have any disincentive to share secret keys

I want to use a CP-ABE scheme to encrypt data to be accessed by multiple unknown (at time of encryption) users. Reading the papers related to CP-ABE, there does not appear to be any disincentive for ...

asked by Andrew Reslan 1 vote

Windows IIS Event/Security Log ID of Private Key deletion of corresponding TLS certificate?

I'm in the middle of writing an MS Active Directory Certificate Services Key Management Lifecycle document for my organization. The primary purpose certificates will serve for this organization is to ...

keys certificates  
asked by PurpleDragon 1 vote
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