2,671 reputation
516
bio website github.com/orlp
location Leiden, Netherlands
age 20
visits member for 2 years, 2 months
seen yesterday

Computer Science undergraduate and cryptography enthusiast. Currently unemployed and looking for opportunities. You can contact me at orsonpeters@gmail.com.

Favourite languages: C++, Python, Rust, C.

Achievements:


1d
revised Is this a valid scheme to authenticate through a 'human-readable' certificate?
added 7 characters in body
1d
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
@RickyDemer I clarified in the question that Eve does not know the answer to the questions at least until the long-term exchange of certificates has completed.
1d
revised Is this a valid scheme to authenticate through a 'human-readable' certificate?
added 77 characters in body
1d
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
@RickyDemer It is right there: "let's assume that Eve does not know the answer to the questions at the time of the exchange". This excludes being able to guess the answers in the timeframe of the exchange.
1d
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
@RickyDemer Just like it's infeasible to guess the private key, I assume the questions are of sufficient quality it's infeasible to guess them, at least within the timeframe of the exchange. The questions I used as an example are weak toy questions. $H$ is a slow hash function, like scrypt.
1d
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
@RickyDemer If bruteforce on the answers is the strongest attack on this scheme, that would qualify it as 'secure', wouldn't it? Your argument could also be used to say public signatures are insecure, because it allows you to check your guesses for the private key.
1d
asked Is this a valid scheme to authenticate through a 'human-readable' certificate?
Feb
21
comment Anonymous Gravatar Problem
The ephemeral key is generated by the site that wants to embed a gravatar. They may choose to cache it for future use, or generate a new one for every gravatar. They shouldn't leak the private key however, as this will expose the hash of the user's email address. The public key is included in the gravatar URL, as said in the answer, so it's public knowledge. The difference between my answer and CodeInChaos's is that I explicitly give a scheme for the URL, display the primitives used and use ECDH rather than ECC.
Feb
17
answered Anonymous Gravatar Problem
Jan
16
comment Why is EdDSA collision-resilient with SHA-512?
Reference to herding attack, pretty easy to understand: cs.haifa.ac.il/~orrd/HashFuncSeminar/OhadLutzky.pdf
Jan
12
comment Where are the ChaCha20 test vectors/examples?
You can generate your own test vectors with the reference implementation.
Jan
7
awarded  Yearling
Oct
28
comment Can you help me understand PFS and wPFS?
@T.B I don't know - I do not have access to that specification (and I'm not going to pay for it, sorry).
Sep
30
awarded  Explainer
Jul
2
awarded  Curious
May
1
comment Is AES still secure considering all this NSA/Snowden scandal?
@JW. Optimized code is more difficult to understand, that is correct. But there should be no excuse for "accidently branching ons secret data". It's very hard to justify any form of branching in crypto code, as often everything is unrolled anyway, and the very few places where you do branch should be on loops with arbitrary data length. There is no excuse for incorporating legacy code that does not follow the same design principles. These are the burdens you take onto you when you write crypto code, but that doesn't make it "hard", or "almost certainly broken with side channels".
Mar
14
comment How is a public key actually used to encrypt something?
@fgrieu I was only explaining to the asker how it would be possible to exponentiate a word document, I did not mean to suggest that it's either secure or practical.
Mar
12
comment How is a public key actually used to encrypt something?
@TylerDurden A form of encryption where you have a small shared secret (the private key - there is no public key), and use that small shared secret to encrypt any amount of data. Examples of such algorithms include AES, Salsa20, and more historic examples are Blowfish and (3)DES.
Mar
12
answered How is a public key actually used to encrypt something?
Mar
9
awarded  Announcer