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Moderator♦ pro tempore on French Language, Computer Science and Software Recommendations. I'm also a unix amateur, and a developer with a computer science background and security leanings by trade.

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Avatar picture slightly adapted from a photo by Luridiformis (Zonda Grattus).


Aug
25
comment What are the advantages of TOTP over HOTP?
This answer makes no sense in relation with the question. TOTP and HOTP are intended as a form of authentication (usually as a what-you-have factor as the values are read off a token). They have nothing to do with other aspects of establishing a secure channel.
Aug
23
comment Seemingly simple decryption question
Although this question is possibly about breaking cryptography, there is too little information to answer it from a cryptographic perspective. It could be a valid question about reverse engineering in general, for which a potential venue would be Reverse Engineering.
Aug
21
comment Digitally sign and verify a file using private/public keys and OpenSSL API
@HenrickHellström This question would be equally off-topic on Information Security. It is a programming question and thus should be posted on Stack Overflow.
Aug
19
comment Simple proof that shows AES is not a uniform permutation on any n-bit string?
@D.W. While this thread is surely related, I don't understand how it answers this question. What does it mean for a specific permutation to be uniform anyway?
Aug
16
comment Security implication of exporting private key
This question appears to be off-topic because it is about tools that happens to be using cryptography, not about the underlying cryptography itself. Since it is about the security properties of these tools, it would be best on Information Security.
Aug
15
comment Advantages of 64-bit CPU smartphone
Actually, there is probably a technical basis for that statement: ARMv8 processors introduce both 64-bit general registers and hardware acceleration for AES and SHA-{1,2}. But the two are not correlated.
Aug
12
comment Security issues of a MAC-then-Encrypt-then-MAC approach?
Background: Should we MAC-then-encrypt or encrypt-then-MAC? Could you comment on why or when one would want plaintext integrity in a way that isn't satisfied by ciphertext integrity?
Jul
28
comment Can you help me understand this “Message Modification by Meet-in-the-Middle” related to Tiger Hash?
Have you read the meet-in-the-middle article on Wikipedia?
Jul
25
comment Are there any Javascript CSPRNGs?
Your question is not clear: you say you want a CSPRNG, and then you talk about an entropy source. Do you need a CSRNG (unpredictable, i.e. at least seeded with a sufficient entropy source), or a CSPRNG (i.e. deterministic, but predictable only by knowing the secret seed)?
Jun
14
comment Strategy for random CTR initial counter values
@RichieFrame While the device can receive and verify signed messages, it needs to be able to emit encrypted messages without having to wait for the control server.
Jun
13
comment RSA decrypting of a huge file by parts
Your question is not clear: are you designing a storage format for that file, or do you have the encrypted file already stored? If the latter, you need to tell us how that file was produced. As the answers here explain, what you're describing, with a huge file somehow encrypted with RSA, is highly atypical. RSA only lets you encrypt a few hundred bits at a time, and slowly, so it's normally used to encrypt a symmetric key which is used to encrypt the rest.
Jun
13
comment Given $n$ bits, how many “truly random” sequences/numbers can be constructed?
@NeilSlater Indeed, I inverted the meaning of pass/fail midway (pass = have the correlation property vs pass = look random). I've reworded that sentence.
Jun
4
comment Padding to increase entropy and size of (otherwise) small JSON objects
@aross Asymmetric encryption is never used for ordinary data directly — it would be technically possible but extremely slow and libraries aren't set up for it. What you do is hybrid encryption: generate a random AES key, use an AES mode to encrypt (and authenticate) the data (your JSON string), and use public-key encryption on the AES key. You can keep using the AES key as long as the other party still has it. JWT only standardizes RSAES-PKCS1-V1_5 for asymmetric encryption, which is not perfect.
May
27
comment Does data authenticity always, implicitly, provide data integrity?
@otus These are different meanings of integrity (or, if you prefer, different settings which both have an integrity property).
May
27
comment Does data authenticity always, implicitly, provide data integrity?
@otus Yes, that's my point. In this sense, HMAC achieves authenticity (if the HMAC is correct, the file has to be mine) but not integrity.
May
27
comment Does data authenticity always, implicitly, provide data integrity?
@otus That assumes that the sender is cooperative, which is often but not always the case (see my backup example).
May
25
comment Reverse engineering a single checksum byte
This question appears to be off-topic because it is not about cryptography. It might be suitable for Reverse Engineering, though more information would probably be required for a useful answer.
May
25
comment Symmetric-Key Based authentication
Bleh. Posting a scan is lazy and rude. If you can't even be bothered to type a question, why should we be bothered to read it? And as for doing your homework, what have you tried?
May
22
comment Which tamper-protection algorithm provides the shortest output?
@D.W. Given the information in the question, there's a generic approach to authentication and confidentiality, but not to freshness. That's why I explain in my last paragraph that replays, and more generally uses out of context, are possible.
Apr
28
comment Can I make a PRNG that is secure even when state can be modified by user?
Related (for a later engineering stage): Evaluating the entropy gathering in a PRNG