Reputation
2,683
Top tag
Next privilege 3,500 Rep.
Protect questions
Badges
5 16
Newest
 Yearling
Impact
~49k people reached

Mar
30
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
While I do not 100% agree with your notions in point #1 and #2, I did not consider the attack where Eve swaps out questions for those she knows the answer with. Do you know of any secure scheme where two human users can prove their identity to eachother through some means without having shared a cryptographical certificate/secret beforehand? Is it possible at all?
Mar
30
accepted Is this a valid scheme to authenticate through a 'human-readable' certificate?
Mar
30
comment Is this a valid scheme to authenticate through a 'human-readable' certificate?
You have no idea how much entropy there is with question/answers, it could be an arbitrary amount. Could you elaborate on your replay attack? I don't fully understand what Eve would replay, and how it would affect security.
Mar
30
comment Is there an existing authorative definition of the cryptographic term 'pepper'
@RichieFrame Forgive me, but isn't giving an advantage to systems with more cores the opposite of what you want? The less parallel an attack, the more expensive it becomes.
Mar
30
revised Is this a valid scheme to authenticate through a 'human-readable' certificate?
edited body
Mar
28
revised Is this a valid scheme to authenticate through a 'human-readable' certificate?
added 7 characters in body
Mar
27
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.
Mar
27
revised Is this a valid scheme to authenticate through a 'human-readable' certificate?
added 77 characters in body
Mar
27
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.
Mar
27
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.
Mar
27
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.
Mar
27
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