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7 votes
Accepted

Are the null bytes produced by a True Random Number Generator a security issue when using it as a source of entropy for keys in One-time pad?

Nope. They happen naturally. And if they didn't, you should be worried as it would indicate that your generator isn't working properly. If your generator is really random, all digits have an equal ...
Paul Uszak's user avatar
  • 15.6k
7 votes

Why does symmetric encryption not provide authentication and integrity? Is it only this type of encryption or cryptology in general have this issue?

Confidentiality vs authenticity Encryption aims at transmitting a secret message, maintaining it's confidentiality. It does not necessarily provide integrity or authenticity. That it to say, even with ...
fgrieu's user avatar
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5 votes
Accepted

Can we use several times the same RSA and ECC keys?

Receiving multiple (RSA) encrypted message does not give more information about the factorization of the public key. Indeed. If the outcome and internals of decryption remain secret, there's a strong ...
fgrieu's user avatar
  • 142k
5 votes
Accepted

What is simple asymmetric encryption that use arbitrary key?

With the standard definition of public key encryption (or signature), it's not possible to make the public key arbitrary†. If it was, the method to find a matching private key from public key would ...
fgrieu's user avatar
  • 142k
4 votes

If I encrypt a plaintext with different keys for each block, will I have the same security as a one-time pad?

No, not necessarily. That depends heavily on the underlying algorithm (AES). Suppose that AES leaks information about one bit (of the input block) with negligible probability $\epsilon $. Then there ...
canary's user avatar
  • 124
4 votes

Are the null bytes produced by a True Random Number Generator a security issue when using it as a source of entropy for keys in One-time pad?

No. Any byte value should have about the same probability, assuming a uniform distribution. If some kind of value, including a "null" byte with all the bits set to zero, is absent then you'd ...
Maarten Bodewes's user avatar
  • 93.2k
3 votes

Double- and -add algorithm

The points of an elliptic curve forms an abelian group under the usual point addition. In finite field case, the order is finite, i.e. the curve has finite number of points. The order can be prime or ...
Titanlord's user avatar
  • 2,307
3 votes
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Is there any cryptography-based assured data deletion technique currently as a standard?

Is there any standardized technique for assured data deletion in the cloud? For some definition of standardized, yes: store data encrypted (symmetrically or with hybrid encryption) in the cloud, with ...
fgrieu's user avatar
  • 142k
3 votes
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Signature Chains: Ensuring Authenticity and Trust

I would concur with your interpretation, although the question is a little vague. When the question says that we trust $Y$ does this mean that we trust $Y$ only to sign messages that are true? Or that ...
Daniel S's user avatar
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3 votes
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May I use the same One-time pad key two times if I encrypt it with a block cipher using two different block cipher keys?

Sure, but you could e.g. guess both keys, guess (part of) the one-time-pad, and then decrypt (part of) the two ciphertext to see if you guessed right with a probability more than 0.5 - assuming that ...
Maarten Bodewes's user avatar
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2 votes
Accepted

CTF - DES Challenge

You seem to have gotten pretty far. Here are my musings. spoiler: some keys can be weak ...
J_H's user avatar
  • 266
2 votes

How to determine the prefix of a SECP256K1 compressed public key

I know that the prefix depends on the last two characters of the uncompressed key. Not the last; is it prefixed,i.e. added to the beginning. In secp256k1, for compression we have the following rule; ...
kelalaka's user avatar
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2 votes
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Is KangarooTwelve hash function suitable for generating very large key material as Shake-256 is?

Sure. They are XOF's just like SHAKE128 and SHAKE256. However, if you'd want to use a non-standardized, reduced round, parallel hash function for key derivation is another question. 2048 bits is still ...
Maarten Bodewes's user avatar
  • 93.2k
2 votes
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Key exchange for encrypted firmware update

The theory is to use a key derivation function after Diffie-Hellman key exchange. A truncated hash would do if a single key is nedded. As DJB puts it (emphasis mine): Given someone else's Curve25519 ...
fgrieu's user avatar
  • 142k
1 vote
Accepted

Is there a way to defeat statistical information leak in Vigenère cipher when the ciphertext is reasonably larger than the key size?

I have been thinking in XORing a keystream of a cryptographically secure hash function in Counter Mode in the plaintext before applying the key, can it defeat statistical information leak? It depends....
poncho's user avatar
  • 148k
1 vote
Accepted

Key blinding security in Ascon

As stated in the Ascon specification, the keyed initialisation and finalisation help prevent key recovery/universal forgery when the internal state is recovered by an attacker during associated data/...
samuel-lucas6's user avatar
1 vote

How to calculate key length in bits?

An example key of 16 hexadecimal numbers was said to be 2048 bits in length If the key is expressed as 16 hexadecimal digits, then that's 16×4 = 64 bits. If the key is expressed as 16 hexadecimal ...
fgrieu's user avatar
  • 142k
1 vote
Accepted

Safe implicit value validation: $H_k(k \oplus m) \sim H_k(m)$?

Are the following two methods roughly equivalent ways of authenticating that the section of key material $k$ is associated with the section of message material $m$? $$H_k(k \oplus m) \tag{a}$$ $$H_k(m)...
aiootp's user avatar
  • 814
1 vote
Accepted

If I encrypt a plaintext with different keys for each block, will I have the same security as a one-time pad?

Yes it is. With a small but important caveat. And the reason is that the key entropy (256 bits) exceeds any possible message entropy (128 bits). Simples. It's easy to read "AES" and infer ...
Paul Uszak's user avatar
  • 15.6k
1 vote
Accepted

Derrive a new key from Trusted Third Party (e.g. Kerberos) session key

In the Kerberos protocol, the authentication process involves using a shared secret key between the client and the Kerberos server to establish a session key. This session key is primarily used for ...
Mmdrza's user avatar
  • 36
1 vote
Accepted

Security of keys that are as long as the data

Yes, it is secure but only if your key is generated truly random. This cryptosystem is called One-Time-Pad (OTP), and has perfect security. Perfect security is the term used for the cryptosystems in ...
m123's user avatar
  • 283

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