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Jan
8
answered Why hash the message before signing it? Digital signature with RSA
Jan
7
comment Relation between key size and PRNG state size
If DSA is weak in the face of bad (160 bits) entropy, could you outline how to break 1024 bit DSA keyed by a CSPRNG with 160 bits of state?
Jan
7
comment Relation between key size and PRNG state size
I didn't give the downvote, but I suspect whoever did downvoted because your answer swerves between correct statements and total nonsense. Statements like "the quality of the output of the PRNG is debatable" is questionable; there exist high quality CSPRNGs that are effectively indistinguishable from random given 160 bits of seed. I have also no idea why you say "160 bits of state is definitely not (enough) for a 1024-bit DSA key". And, your general answer of "no, you cannot use a n-bit state RNG to generate an RSA key with n or more bits of size" is wrong.
Jan
6
comment How to judge if my work is meaningful in cryptography?
You might want to clarify what precisely you mean. Do you mean that, if you've done a trial decryption, how do you check if the result is meaningful? Or, do you mean that, if you've generated a cryptographical result (either a new cryptographical primitive, or a cryptanalytic attack), whether this result is meaningful (significant)?
Jan
5
comment In this example, which is a premaster secret, and which is a master secret?
If the question is about terminology, I would have to agree with @fgrieu ; the terms "premaster key" and "master key" are not standard terminology; at the least, I've never heard of them either. It might be terminology someone made up; if so, you'd have to ask them what they meant. The closest standard terms I can think of is the TLS terms "premaster secret" and "master secret" (which are intermediate values derived during the TLS key exchange protocol, and differ from what you have referenced)
Jan
3
answered Where does the $\varphi(n)$ part of RSA come from?
Jan
3
comment How does Clifford Cocks 'Non-Secret Encryption' work?
In addition to Thomas's correct comment, there is an alternative way to look at this; Cocks message is precisely RSA with $N=e$; that is, the same value is used for the modulus and the public exponent. What Mr. Cocks specifies for decryption is the standard method for doing RSA decryption using the Chinese Remainder Theorem; details on precisely how to do that is spelled out in, for example, PKCS #1.
Jan
3
comment Keeping IV secret for AES CFB mode
@M.C.: Actually, there's nothing wrong with CFB mode if you know what you're doing; you pick unique IVs, and perform some form of integrity checking (e.g. use a MAC).
Jan
2
awarded  Nice Answer
Dec
23
revised Coefficients in Shamir's Secret Sharing Scheme
Added exception
Dec
22
answered Coefficients in Shamir's Secret Sharing Scheme
Dec
22
answered Forgery Attack Against RSA Digital Signature
Dec
22
comment Keeping IV secret for AES CFB mode
I disagree with the "possible duplicate" comment; it's about CFB mode, which is subtly different than the modes discussed there; those subtle differences merit examination.
Dec
22
answered Keeping IV secret for AES CFB mode
Dec
22
comment What are the advantages of CBC over ECB?
@Thomas: no, you cannot generate the second picture from the third. If you were thinking about somehow undoing the xor that's in CBC mode, remember that you do the xor and then you encrypt with the block cipher; that means, to undo the xor, you would need to decrypt first, and you can't do that unless you have the key.
Dec
22
answered What are the advantages of CBC over ECB?
Dec
21
answered Can we say that if $P=NP$ there is no CPA secure public key encryption?
Dec
21
answered What happens to entropy after hashing?
Dec
20
answered Can $r$ and $s$ from an ECDSA signature be negative numbers?
Dec
20
comment Can $r$ and $s$ from an ECDSA signature be negative numbers?
If it's DER, then that's your answer; DER integers always have the high bit of the integer being the sign; if the msoctet has its high bit, then you prepend a 0x00 byte to preserve this property.