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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).


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
Apr
25
comment State of the art RSA key generation
This doesn't answer the question at all. It isn't asking for a basic explanation of RSA, it's asking about what constraints on the two primes must be checked to avoid security pitfalls.
Apr
23
comment Spurious keys filter
I'm not sure I understand the question. Are you looking for keys that would map a given plaintext to some ciphertext containing only printing characters? Or for keys that would map any plaintext consisting only of printing characters to a ciphertext consisting of only printing characters? What do you mean by “spurious keys” (are you sure you're using the right English word here?)? Are you using “confusion” in the technical sense, and if not what do you mean? Where does key derivation come in?
Apr
22
comment Key construction in the Full Cramer-Shoup cryptosystem
I don't understand your last sentence. What do you mean by “use the less private keys”? Could you give an example?
Apr
13
comment How do they implement MAC in TLS?
@CuriousSam TLS “packets” (called records in the specification) are unrelated to how the stream is broken down into TCP packets.
Apr
9
comment How to attack a classical cipher using known partial plaintext?
Welcome to Stack Exchange. This answer would be more interesting if you described some algorithms to detect classical ciphers, rather than just linking to some code (whose operating principle isn't even described, at least not at that URL).
Mar
31
comment Testing hardware random number generators?
possible duplicate of How random are commercial TRNGS
Mar
24
comment What is the difference between known-plaintext attack and chosen-plaintext attack?
Well, ok. Raw RSA is a cryptographic algorithm, but it isn't a (good) encryption or signature algorithm. The key point is that signing a plaintext is not the same operation as decrypting a ciphertext. They typically use different keys (because they should have different management policies), and the padding is different.