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1500 questions
16
votes
0 answers
Fewest qubits required for the discrete logarithm problem and integer factorization
According to a paper from 2002, the most efficient circuit to factor an $n$-bit integer requires $2n+3$ qubits and $O(n^{3}\lg(n))$ elementary quantum gates, assuming ideal qubits. Later on, according to a paper from 2008, it is shown that it…
forest
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16
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Has Telegram security been significantly improved with MTProto 2.0?
Telegram messenger's original encryption scheme, MTProto 1.0, has been shunned by most cryptographers for a number of reasons, like being vulnerable to IND-CCA attack; being unorthodox in general, making unusual applications of hashing and key…
Dark Lotus
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16
votes
1 answer
Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme
Shamir's original paper (PDF, 197kb) describing a threshold secret sharing scheme states:
To make this claim more precise, we use modular arithmetic instead of
real arithmetic. The set of integers modulo a prime number $p$ forms a
field in…
ampersand
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16
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1 answer
Relation between Key-exchange and Public-Key encryption schemes
Recently we have seen a lot of papers on Post-quantum key-establishment (key encapsulation mechanism or Key-exchange), largely due to the standardization call of NIST for PQ-protocols. However, most of the work for example : Kyber, NTRU-prime,…
Rick
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16
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1 answer
Who issued the first SSL certificate?
When SSL was introduced in ~1996, there was only a few CAs issuing certificates for that specific use and a few sites which actually used SSL.
Which Certification Authority issued the first SSL certificate and whom was it issued to?
Mark
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16
votes
4 answers
Looking at hash output – is Base64 encoding in any way better than HEX encoding?
I was wondering why most "normal/unsafe" crypto hashes like SHA-256, SHA-512, Whirlpool, RipeMD-160, MD5, etc. are HEX encoded.
But most "secure" crypto hashes (KDF' ) like bcrypt and scrypt are Base64 encoded. Why?
somewhere I heared that Base64…
Richard R. Matthews
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16
votes
2 answers
Is digest=HASH(HASH(a)+HASH(b)) equivalent to publishing two digests?
Is combining digests (created using a hash function) using arithmetic addition, and then hashing and publishing the result, less secure than publishing the set of digests?
Does the answer change if the outer hash function is different from the inner…
gavinandresen
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16
votes
4 answers
Is using a broken SHA-1 for password hashing secure?
Recently the hashing collision issue of SHA-1 was discovered. Identical hash values for 2 separate PDF files were generated. Does that make SHA-1 any unsafe for using it only for password hashing?. The probability of two different password to match…
Rohith K D
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16
votes
1 answer
What is a (smooth) projective hash function?
I recently came across the term "smooth projective hash function", and I see that there are many constructions nowadays that rely on them, especially some PAKE constructions. But, I didn't exactly understand them. What are they? And why are they so…
typos
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votes
1 answer
If a hash function $H$ is collision resistant, is it true that $H(x)\neq H(x')$ for all messages $x, x'$ with $x \neq x'$?
I am puzzled with a question that seems to be based on theory.
If there is a collision resistant hash function (since it is not possible for a hash function to be collision free, this is a theoretical question),
would it be true to say that there…
QWASH
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16
votes
3 answers
Is it better to maximize memory usage or number of passes with Argon2i 1.3?
I wrote a small application that uses Argon2i for deriving symmetric keys for encryption of local files and secret Curve25519 keys. Argon2i v1.3 is susceptible to TMTO attacks if the number of passes is below 10, according to the most recent paper …
user40185
16
votes
1 answer
Why not use `<`, `>` or `==` in constant time comparison?
I am comparing secret data stored in arrays a and b to see which holds a greater value. My current (pseudo)code looks like this:
unsigned char smaller = 0, bigger = 0;
for (i = 0; i < size; ++i) {
smaller |= (!bigger) & (a[i] < b[i]);
bigger…
Sebastian
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16
votes
6 answers
Why MACs are so important despite digital signatures doing everything a MAC can do and more?
When an entity $A$ wants to send a message to entity $B$, he can attach a MAC to the message. Entity $B$ on receiving the message can use the pre-shared key to compute the same MAC and confirm if the message is untampered with.
This approach…
Minaj
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16
votes
2 answers
Why is the salt used only once in PBKDF2, while the password is used often?
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor…
ericball
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Name of an archaic type of RSA padding (0BBBBBBB...)
In some legacy code, I encountered RSA signature padding in the following format (hexadecimal):
0B BB BB BB BB BB BB ... BB BB
Is there a name for this simple type of RSA padding? I would think that the original developers got this design…
Myria
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