instruction stringlengths 15 30k |
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Given the cipher
$$E(k, m) = m \oplus k \oplus \operatorname{rev}(k)$$
where $\operatorname{rev}(k)$ is the reversed binary of $k$, how would one prove that the cipher is not perfectly secret.
I know that the definition of perfect secrecy is $P(M = m \mid C = c) = P(M = m)$ for all $m$ and $c$ and that each key i... |
Given an encryption system where $c\equiv m^x\ (mod\ p)$, $p$ is a known prime,
Is it possible to recover $x$ with a known plaintext attack? (Given (p,m,$c\equiv m^x$))
|
Given an encryption system where $c\equiv m^x \pmod p$, $p$ is a known prime,
Is it possible to recover $x$ with a known plaintext attack? (Given $(p,m,c)$)
|
Given an encryption system where $c\equiv m^x \pmod p$, $p$ is a known prime,
1. Is it possible to recover $x$ with a known plaintext attack? Given $(p,\text{factorization of }\varphi(p),m,c)$
2. Is it possible to recover $x$ with a chosen plaintext attack? (Somehow with the chinese remainder theorem on the facto... |
In combining $RSA$ system into $LSB$ steganography system in bmp image, Since every pixel of image is beteen $[0,255]$ integer numbers, if we choose $p$ and $q$ that $N=p*q>255$, How embedding message that encrypting with $RSA$ in image? |
I want to implement the following [homomorphic encryption](https://en.wikipedia.org/wiki/Homomorphic_encryption) scheme from [On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption](https://eprint.iacr.org/2013/094) by Lopez-Alt et al. I use C++ and I want to know before start to write... |
How to test an implementation of a homomorphic scheme? |
Currently I am trying to understand random oracle model in order to make a small presentation about it but I seem to be very confused about it.
Since it's an hypothetical model without a real life application (no function can be completely random), how cryptographic functions are modeled as random oracles (e.g are a... |
Is there an algorithm to hide text in another text, while preserving the meaning of the latter? |
I was reading this paper [Homomorphic evaluation of the AES Circuit](https://eprint.iacr.org/2012/099.pdf) by Gentry et al. when I thought if something similar can be done with DES or 3DES, e.g. it is plausible to decrypt DES homomorphically ? |
I need an example of Elliptic ElGamal Public Key Cryptosystem. I have been trying with some values but I don't get the right solution.
I have $p=13$, the elliptic curve $E:y^2=x^3+11x+7$ and a point $P=(6,\sqrt{3}) \in E(\mathbb{F}_{13})$.
The message is $M=(0.5,12.625)\in E(\mathbb{F}_{13})$.
Alice, chooses... |
I'm trying to investigate different key wrapping algorightms for my implementaiton. I've noticed that AES-SIV is very rarely implemented by most of open source libraries. Most of them implements key wrap from RFC 3394.
It's a bit weird, as AES-SIV has many nice properties and (maybe I'm wrong) seems like best choice... |
I found (through some reverse-engineering) that the following encryption scheme is used in a commercial software that is quite widely used in Germany (Security by obscurity at its best).
I have the following two questions:
1. Is this encryption scheme known in the literature, or is it a variation of a known sch... |
As shown in http://crypto.stackexchange.com/questions/31807/why-does-my-ssh-private-key-still-work-after-changing-some-bytes-in-the-file a typical RSA private key file contains.
> - The public modulus $n$ and exponent $e$;
> - The private exponent $d$;
> - The prime factors $p$ and $q$ of $n$;
> - The "reduced" p... |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme, so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant k and these ciphertexts to Bob. Can Bob do the following homomorphic operations?
$$d_1=Enc_{k_n}(m_1)*k=Enc... |
Can homomorphic operations on many different ciphertexts be multiplied by a same constant? |
As shown in http://crypto.stackexchange.com/questions/31807/why-does-my-ssh-private-key-still-work-after-changing-some-bytes-in-the-file a typical RSA private key file contains.
> - The public modulus $n$ and exponent $e$;
> - The private exponent $d$;
> - The prime factors $p$ and $q$ of $n$;
> - The "reduced" p... |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme, so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant a , some random numbers $a_1$,...,$a_n$ and these ciphertexts to Bob. Can Bob do the following homomorphic op... |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme, so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant a , some random numbers(matrices) $a_1$,...,$a_n$ and these ciphertexts to Bob. Can Bob do the following homo... |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme, so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant a , some random numbers $a_1$,...,$a_n$ and these ciphertexts to Bob. Can Bob do the following homomorphic op... |
I was playing with a function that I think is collision free and uninvertible assuming the hardness of integer factorization. I am unfortunately not as skilled at math as I would like to be, and do not know how to prove or disprove the function as being collision free. My only proof so far has been from unit testing al... |
I'm trying to understand to padding process of MD5 from the link :http://www.ietf.org/rfc/rfc1321.txt
In this link I have found the following description of padding:
**The message is "padded" (extended) so that its length (in bits) is
congruent to 448, modulo 512. That is, the message is extended so
that it... |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme, so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant a , some random numbers $a_1$,...,$a_n$ and these ciphertexts to Bob. Can Bob do the following homomorphic oper... |
I'm trying to understand to padding process of MD5 from the link : <http://www.ietf.org/rfc/rfc1321.txt>
In this link I have found the following description of padding:
**The message is "padded" (extended) so that its length (in bits) is
congruent to $448$, modulo $512$. That is, the message is extended so
... |
I'm trying to understand to padding process of MD5 from the link: <http://www.ietf.org/rfc/rfc1321.txt>
In this link I have found the following description of padding:
> The message is "padded" (extended) so that its length (in bits) is
congruent to $448$, modulo $512$. That is, the message is extended so
... |
I was playing with a function that I think is collision free and uninvertible assuming the hardness of integer factorization. I am unfortunately not as skilled at math as I would like to be, and do not know how to prove or disprove the function as being collision free. My only proof so far has been from unit testing al... |
Let's say our message is *b* bits long. When we're done padding it, it should look like this:
P = [ Message | Padding | Message length ]
|<- b bits->|<-- ??? bits --->|<--- 64 bits --->|
Where the message length is just *b* encoded as a 64-bit integer, and the middle padding section look... |
Why is CBC-MAC with length appended not secure? |
I'm trying to investigate different key wrapping algorithms for my implementation. I've noticed that AES-SIV is very rarely implemented by most of open source libraries. Most of them implements key wrap from RFC 3394.
It's a bit weird, as AES-SIV has many nice properties and (maybe I'm wrong) seems like best choice ... |
Why is AES-SIV not used, but AESKW, AKW1? |
AES-GCM has a limit on the length of the plaintext it encrypts: 2^39 - 256 bit. But is this limit per key or per (key, nounce)? That is, if I encrypt a message with the maximum length, and encrypt another message with the same key but different nounce, will it be secure still? |
Is the length limit of AES-GCM per key or per (key, nounce) pair? |
How to generate composite order group using PBC library? With PBC library, element_init_G1(g,pairing) statement creates element 'g' for group of prime order.
I want to know how element of composite order group is created ? |
AES-GCM has a limit on the length of the plaintext it encrypts: $2^{39} - 256$ bits. But is this limit per key or per (key, nonce)? That is, if I encrypt a message with the maximum length, and encrypt another message with the same key but different nonce, will it be secure still? |
Is the length limit of AES-GCM per key or per (key, nonce) pair? |
Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme (BHHO), so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice sends a constant a , some random numbers $a_1$,...,$a_n$ and these ciphertexts to Bob. Can Bob do the following homomorph... |
How to generate composite order group using PBC library? With PBC library, `element_init_G1(g,pairing)` statement creates element $g$ for group of prime order.
I want to know how element of composite order group is created. |
It is proven that ECDSA algorithms are faster in key and signature generation compared to RSA. In addition, the signatures are much shorter.
However, I would like to know the performance difference of the variants ECKCDSA and ECGDSA compared to either ECDSA or RSA. ECGDSA avoids the calculation of the inverse in the... |
I just check all the questions with scrypt tag about that and usually it's said that scrypt is nice in theory and theoretically better than bcrypt and PKDF2, but it's too young to be "completely safe".
bcrypt is very old and yet unbroken but since it uses relatively little amounts of ram crackers can get around it ... |
It is proven that ECDSA algorithms are faster in key and signature generation compared to RSA. In addition, the signatures are much shorter.
However, I would like to know the performance difference of the variants ECKCDSA and ECGDSA compared to either ECDSA or RSA. ECGDSA avoids the calculation of the inverse in th... |
Is there any notion of a periodic OWF?
I.e. an OWF $f$ that on every input $x$ in its domain it holds that $f(f(f\ldots f(x))\ldots )=x$ when $f$ applied many times, each time on the previous output.
Also, if we take some One Way Permutation, it must be periodic of course. So is it guaranteed that its period ... |
I need a basic understanding of Homomorphic Encryption. I read some topic and I learned a difference between fully and partial but I want know the step by step movement of algorithm.
So for a private key algorithm (in general) the step by step is:
2 user --> u1 e u2
u1 --> publicKey and privateKey (pu1, ... |
Hello i'm reading a paper based on Homomorphic Encryption.
[Link][1]
[1]: https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201407fa5.html
Now, i need a diagram of this algorithm if possible with all the operation that the sender of cyber text do.
I'm reading the text and i encountered so... |
I (for a test) just randomly altered a private RSA key by opening it up in Vim and changing a few bytes. It is the private part of an SSH key pair used for logging in on a remote system. Puzzlingly, it still allows me to login.
I did some research and found that it is a base64 encoded ASN.1 container, so I pulled al... |
If you happen happen to have a message $m ∈ Z_n / Z^*_n$, RSA works but not secure. How likely is it going to happen? $|n|=1024$ bits $|p| = 512$ bits $|q| = 512$ bits. |
If you happen happen to have a message $m ∈ Z_n \backslash Z^*_n$, RSA works but not secure. How likely is it going to happen? $|n|=1024$ bits $|p| = 512$ bits $|q| = 512$ bits. |
My situation: I've been working now for a couple of months on my own unique hash function, I've changed it many times and had two main versions but I won't bore anyone with the details of my work; at least not here. I'm here to ask a question that's specific and helpful to anyone attempting to design a cryptographic ha... |
Is finding collisions in a (part) hash too often any worse than not often enough? |
Is finding collisions in a part-hash not often enough a bad problem? |
In many homomorphic encryption scheme, a security parameter is calculated as p =O(n).
How to use the complexity order as values?
Is there any specific method with an appropriate example? |
My situation: I've been working now for a couple of months on my own unique hash function, I've changed it many times and had two main versions but I won't bore anyone with the details of my work; at least not here. I'm here to ask a question that's specific and helpful to anyone attempting to design a cryptographic ha... |
Completly crypto noob here.
I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy:
- f(f(msg, key1),key2)=msg
- f(f(msg, key2),key1)=msg
- key1 != key2
Does such cryptosystem exist?
It is ok if it's not Fort Knox secure, I want it to play with my nephews but I don't mind go... |
does "Commutative" Asymmetric system exist? |
Completely crypto noob here.
I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy:
- f(f(msg, key1),key2)=msg
- f(f(msg, key2),key1)=msg
- key1 != key2
Does such a cryptosystem exist?
It is ok if it's not Fort Knox secure, I want it to play with my nephews but I don't mi... |
Does a "commutative" asymmetric system exist? |
I just check all the questions with scrypt tag about that and usually it's said that scrypt is nice in theory and theoretically better than bcrypt and PKDF2, but it's too young to be "completely safe".
I understant bcrypt is very old and yet unbroken, but since it uses relatively little amounts of RAM crackers can ... |
When will scrypt be "old enough to be safe"? |
Completely crypto noob here.
I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy:
- g(f(msg, key1),key2)=msg
- g(f(msg, key2),key1)=msg
- key1 != key2
Does such a cryptosystem exist?
Ideally I'd like f and g, to be the same function, but I'm ok if they are different.
... |
I'm currently looking into creating some compact merkle tree branches to prove that a given hash was included in a given merkle root. My initial thought was to list the leaf, the merkle root and all of the hashes that the given leaf was combined with to make the merkle root.
So in this example:
[, and fkraiem's answer to it, made me wonder about the security and practicality of using "symmetric RSA" to provide a partially compromise-resistant secure channel.
Specif... |
I am working in a very bandwidth restricted environment where I from time to time have the need to distribute public keys.
It is my understanding that the public key, in compressed form, takes up the space of the curve size+1, e.g. 160 bit curve gives 161 bit public key. However, the output from OpenSSL gives me a m... |
Can I shorten the large public key output file from OpenSSL? |
I am working in a very bandwidth restricted environment where I from time to time have the need to distribute public keys.
It is my understanding that the public key, in compressed form, takes up the space of the curve size+1, e.g. 160 bit curve gives 161 bit public key. However, the output from OpenSSL gives me a m... |
I am working in a very bandwidth restricted environment where I from time to time have the need to distribute public keys. The distribution happens in bit format, so there is no need for encoding, at best I would like all my data "raw".
It is my understanding that the public key, in compressed form, takes up the spa... |
I am working in an environment with strict bandwidth requirements, and we need predictable bit lengths of the stuff we send. We need to broadcast ECDSA public keys, and we are using OpenSSL to generate them.
So will the prublic key lengths vary from private key to private key? Or will they be constant?
I noticed ... |
Are the ECDSA public keys of a stable/fixed length relative to curve size? |
Can I shorten the large ECDSA public key output file from OpenSSL? |
This is not quite an answer, because what I'll discuss is only about as powerful as the attack in the question, which refers to section 3 onwards in: Abderrahmane Nitaj and Tajjeeddine Rachidi, _Factoring RSA moduli with weak prime factors_ (preliminary 2015-05 [eprint][1]).
The method I'll discuss is acknowledged i... |
Asn1parse to the rescue.
Most of the overhead is from the base64 encoding and the PEM header and footer.
The raw size of the compressed form ASN1 encoding is just 44 bytes for my dummy key.
And 22 of those bytes are for the 161 bits of the actual public key.
$ openssl asn1parse -in compressed_public.pem... |
Asn1parse to the rescue.
Most of the overhead is from the base64 encoding and the PEM header and footer.
The raw size of the compressed form ASN1 encoding is just 44 bytes for my dummy key.
And 22 of those bytes are for the 161 bits of the actual public key.
$ openssl asn1parse -in compressed_public.pem... |
Asn1parse to the rescue.
Most of the overhead is from the base64 encoding and the PEM header and footer.
The raw size of the compressed form ASN1 encoding is just 44 bytes for my dummy key.
And 22 of those bytes are for the 161 bits of the actual public key.
$ openssl asn1parse -in compressed_public.pem... |
HKDF is used in one of my projects to derive separate keys from a common master key. But profiling has shown it to be the performance bottleneck under certain circumstances. Is there any faster alternative? The only things I get after googling "key derivation function" are HKDF and password stretching algorithms like P... |
The SHA-256 (as well as any cryptographically secure hash algorithm) produces output that will appear like an uniformly random sequence to observer who does not know the input.
Quite a few random number generators, for example ANSI X9.31's RNG and NIST SP 800-90 Hash_DRBG use SHA family hash functions for the reason... |
In Simplified DES algorithm, the plain text is 8-bit & the key is 10-bit, why is that, why can't both be of 8-bits each? |
Simplied DES why 10-bit key? |
Let $P$ and $Q$ are two points of NIST elliptic curve $E$ (defined over $F_{2^m}$ with prime $m$) and $k$ is a private key such that $k.P=Q$. Also we have a machine that is able to leak some information about $k$. If $k$ be an odd number this machine say $k$ is odd, else return two points $\frac{k}{2}\cdot P $ and $P'$... |
Can we break ECDLP with this machine? |
book ciphers record positions of words. other ciphers turn the content of the message into a pseudo random data stream. without the book the words in a message are unknown. and since the ciphertext doesnt record the message just the postion of words in public text.
how would somebody go about cracking a book cipher... |
book cipher be cracked without key? |
book ciphers record positions of words. other ciphers turn the content of the message into a pseudo random data stream. without the book the words in a message are unknown. and since the ciphertext doesnt record the message just the postion of words in public text.
how would somebody go about cracking a book cipher... |
book ciphers record positions of words.
other ciphers turn the content of the message into a pseudo random data stream.
without the book the words in a message are unknown.
and since the ciphertext doesnt record the message just the postion of words in public text.
how would somebody go about cracking a book... |
I'm going paperless, and I want to encrypt the documents that I scan. I'd like to use CommonCrypto to perform AES-XTS encryption on each file. I'm a software engineer, and I like the idea of being able to write my own wrapper around the library. However, I am not a crypto expert by any means. If I understand IVs and sa... |
Studying for CISSP these choices seemed limited:
> What is the advantage of digital signatures over message authentication codes?
> 1. Digital Signature provides integrity verification while message authentication code does not
2. Digital Signature provides confidentiality while message authentication code does ... |
Can someone elaborate on how 'signing' is done using AES- CMAC and AES-HMAC?
HMAC Signing as I understand: Compute the HMAC( Hash the key and the input concatenated in a special way) Verification: Verify if for the given input and secret key the calculated HMAC(signature) is the same as that is computed. But how is ... |
Difference between AES CMAC and AES HMAC? |
From my understanding man-in-the middle attack works as follow:
Alice and Bob agreed to use Diffie-Hellman using a and q. Alice sends YA. Before it reaches Bob,
Charlie intercepts it and sends YC1 instead. Bob believes to have agreed on a key KB with Alice, but
the key is actually only shared by Bob and Charlie s... |
What 'container' is used normally to store/transport secret keys(for symmetric algorithms)?
I have come across PKCS12 format where a public key(certificate) as well as a private key can be bundled together and stored in an archived file format.
Similarly how can an array of random bytes that can be used as a secr... |
I am working in a very bandwidth restricted environment, and we are looking to implement ECDSA digital signatures. Although they are no longer recommended, we might be looking to use curves that are not listed as supported by most libs, including OpenSSL: https://en.wikipedia.org/wiki/Comparison_of_TLS_implementations#... |
Are low security curves for ECDSA not supported? |
I am working in a very bandwidth restricted environment, and we are looking to implement ECDSA digital signatures. Although they are no longer recommended, we might be looking to use curves that are not listed as supported by most libs, including OpenSSL: https://en.wikipedia.org/wiki/Comparison_of_TLS_implementations#... |
I am developing a simple web app that uses asymmetric encryption, but I am not sure whether to chose RSA or DSA. What are your suggestions?
Thank you |
Should I use RSA encryption since RSA is said to be broken by NSA? |
From my understanding man-in-the middle attack works as follow:
Alice and Bob agreed to use Diffie-Hellman using $a$ and $q$. Alice sends $Y_A$. Before it reaches Bob,
Charlie intercepts it and sends $Y_{C1}$ instead. Bob believes to have agreed on a key $K_B$ with Alice, but
the key is actually only shared by Bo... |
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