4
votes
1answer
99 views

OCB and GCM security

Is OCB as secure as GCM or CCM ? Since OCB design is quite different from GCM and CCM, I was wondering if the security properties of these latters are satisfied by OCB, as well. Thank you.
1
vote
3answers
181 views

How is the following different than RSA Signing of a document?

If the goal is to demonstrate that you are who you say you are, I think the following will work: Bob wants to know that you are Amy. Bob encrypts a number using Amy's public key and then asks her what ...
1
vote
1answer
59 views

Is MAC algorithm same at both sender and receiver end

The MAC algortihm which is used along with a secret key to generate a MAC tag on the sender end ,is it same at the receiver end also who again uses a MAC algorithm to generate a tag? If yes, then how ...
0
votes
1answer
55 views

How to make a document truly read only

How is it possibile to cryptographically make a document truly read only? As in read only I imply that the user can obviously view it which can be achieved by coding which pixels have which colors. ...
6
votes
3answers
6k views

Can Pre-Paid Cards be cracked?

Is it possible to deduce the original function that used to generate those prepaid cards number that are used for charging your mobile phone credits? For example: If I've collected about 1000 of ...
3
votes
1answer
181 views

Repeatable crypto

Is there a safe way to do crypto that will always produce the same result for a given input? My use case is transferring deltas of huge files, to a backup server. The backup server has no knowledge ...
-2
votes
1answer
88 views
0
votes
1answer
46 views

FSB Hash Functions and Convetional hash Functions

I'm reading FSB cryptographic hash function and the authors say that security of this function depends on NP-Complete Problem: "Decoding Linear Code Unlike most other cryptographic hash functions in ...
2
votes
1answer
163 views

SIMONs Cryptoanalysis

I'm reading Cryptanalysis of the SIMON Family of Block Ciphers. In Section 3.1, it says: For SIMON, consider an n-bit input difference $\alpha= x\oplus x'$ to $F$ of Hamming weight one. As the ...
1
vote
1answer
778 views

Is SHA related to AES or TLS in any way

I have been reading about SHA-2 family and I found a lot of in depth details, but I am confused about how it is related to TLS and AES. TLS encrypts data between server and client, but does it make ...
2
votes
1answer
109 views

Is multiple encryption using NaCL and TLS better?

In general, the idea of multiple encryption sounds interesting - for creating stronger cyphers (especially against implementation bugs), one could always get the configuration details wrong and mess ...
2
votes
1answer
133 views

Prevent MITM attack while encrypting data by using ElGamal ECC?

I am using ElGamal ECC to encrypt my plain text data. I want to ensure that my data is safe from a Man-In-The-Middle attack. What methodology I can adopt to achieve this goal? How can we prevent a ...
4
votes
1answer
131 views

CBC-MAC based on PRF

Why is the block cipher in the CBC-MAC taken to be a pseudo random permutation (PRP) and not a pseudo random function (PRF)? We don't need the bijective property of the PRP. So why go with it?
1
vote
0answers
116 views

Should layered use of crypto always have a cryptographic binding between the layers?

Reading the latest TLS weakness, it seems that multiple weaknesses have been found over the years caused by not ensuring that messages are sent over the same channel, and in general a lack of ...
8
votes
3answers
1k views

Desirable S-box properties

What desirable properties should an S-box have? My current standard selection process is to just pick them at random and verify that they fit the following criteria: The probability that any random ...
3
votes
3answers
192 views

Asymmetric algorithm for one time signing of small cleartext

I want to generate a key pair such that the private key can be used once to sign a small message (1024 bytes) at some indeterminate point in the future and the public key can be used to verify that ...
3
votes
1answer
125 views

Secure Deduplication and Encryption in a data store

Assume: We have a centralized data store that can store whatever we need Every user is online Function $f : File \to Key$ gets access to the store, and is the same for all users. $g : Key \to File$ ...
1
vote
2answers
576 views

garbled circuit vs fully homomorphic encryption

Consider an outsourced database to an untrusted cloud (think CryptDb), the question is how to compute a function $f(.)$ on the data. I think I understand how (fully or partially) homomorphic ...
1
vote
0answers
79 views

Are partial hashes used in cryptographic protocols?

In my question (and answer) about a partial hash code used within a signature application I found out that partial hash codes are sometimes used within protocols with a relatively restricted security ...
17
votes
5answers
3k views

Could RDRAND (Intel) compromise entropy?

I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially be influencing Intel to weaken or create backdoors in their design. This petition was ...
2
votes
1answer
381 views

Hash collision resistance requirements for Lamport signatures

According to the original paper, Lamport one-time signature scheme uses two one-way functions: $F$ and $G$. The former one, $F$, is used to create a public key by hashing elements of the private key ...
0
votes
2answers
234 views

Homomorphic Encryption: how does the equality test on ciphertexts work?

Let's suppose we have a asymmetric crypto-system $H$ which is homomorphic with respect to some function $F$. Alice encrypts a message $m$ with her private key $e$ in the crypto-system $H$ and ...
5
votes
2answers
668 views

What are Cryptographic Multi-linear Maps?

I've encountered this term many times in the fields of Fully-Homomorphic Encryption and Obfuscation. I want to learn those subject and Cryptographic Linear Maps seems to be an obstacle in the way. ...
3
votes
0answers
67 views

Managing data permissions/access through asymmetric cryptography

I want to manage authorization, as 3rd-party permissions, through asymmetric cryptography. I'm concerned about how is it possible to share access of encrypted data with N entities, and be able to ...
1
vote
1answer
457 views

How should I treat a new cipher release like Spritz?

I have been looking at both the paper as well as the sourcecode of Spritz — a spongy RC4-like stream cipher and hash function by Ronald L. Rivest and Jacob Schuldt. The paper states We have also ...
3
votes
1answer
94 views

Implementing the Mceliece Encryption - making the Generator Matrix

I am working on an implementation of the Mceliece Encryption system (MCE) and the Niederreiter encryption system. I have been through the basics of finite fields, polynomial arithmetic and some coding ...
2
votes
0answers
204 views

practically verifying block ciphers strength [closed]

How do we verify practically the strength of a block ciphers? Most of the security analysis of block ciphers is usually around theoretical analysis and proofs in some random oracle model etc. For ...
2
votes
1answer
79 views

Question on Waters IBE

I'm reading “Efficient Identity-Based Encryption Without Random Oracles” by Brent Waters. In Page 9, I don't know how ...
3
votes
2answers
255 views

Composition of block ciphers and 3DES

There is some intriguing things about DES and 3DES. Now, I know that DES is weak and 3DES was an attempt to construct a more secure block-cipher from a deprecated one. Having this in mind, what ...
6
votes
3answers
539 views

Are there other digital certificate formats than X.509?

Hi I am a little new to security, but in researching digital certificates it seems the only format people describe is X.509. Are there other formats? If so what are they and where can I find ...
5
votes
2answers
202 views

Choice of authenticated encryption mode for whole messages

There are several well-regarded block cipher modes for authenticated encryption which have made their way into standards and protocols: CCM, EAX, GCM, OCB, … If I am designing a new messaging or ...
15
votes
1answer
2k views

Why do new versions of TLS use an explicit IV for CBC suites?

SSL 3.0 and TLS 1.0 used an insecure scheme to generate implicit IVs when encrypting records in CBC mode: they used the last part of the previous record, a value that can be predicted by the attacker. ...
-5
votes
4answers
171 views

Solution with high decryption cost and low encryption cost

I am looking for any cryptographic solution that will meet those requirements : Only known method to get the encrypted string need to be brute force. Decrypting on modern computer not more than ...
5
votes
1answer
156 views

How would you encrypt-then-MAC when using pen-and-paper and a Caesar cipher?

I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Caesar cipher and they're successfully playing ...
6
votes
3answers
374 views

Good challenges for a crypto competition for teenagers

I'm holding a cryptography workshop for teenagers (around 16 years old) at our university. As part of the workshop, I'm planning to run a crypto competition with prizes: there will be different tasks, ...
0
votes
2answers
273 views

Proving HMAC collision probability bounds?

Could someone point to results or proofs about the probability of $$HMAC(k, m_1) = HMAC (k, m_2)$$ assuming the underlying hash function is SHA-256? Would those probabilities be higher/lower if $m_1$ ...
2
votes
1answer
79 views

How can finding a collision help an attacker with tampering messages with HMAC

As stated in the HMAC RFC (RFC 2104): The strongest attack known against HMAC is based on the frequency of collisions for the hash function H. How can a collision benefit an attacker? I would ...
4
votes
1answer
265 views

How does Random Oracle and Standard Model differ? [duplicate]

I am new to Crypto field. Many papers are boasting of not using Random Oracle model. Instead, those prove security in Standard Model. I am surprised how do these models differ. Can anyone please ...
1
vote
1answer
231 views

RSA was rejected by which journal?

Is it true that first time RSA algorithm was rejected by a journal?
2
votes
1answer
217 views

Why are some key stretching methods better than others?

I'm trying to understand why some key stretching methods are better than others. The wikipedia article presents 3 different key stretching methods: A collision prone simple key stretching ...
5
votes
1answer
132 views

Understanding Genkin-Pipman-Tromer's ground potential, side channel attack on RSA

I'm pretty sure that by now folks might have come across this research from Genkin-Pipman-Tromer (GPT) on extracting the RSA key used by GnuPG (GPG) just by measuring the ground potential. I'm going ...
0
votes
3answers
619 views

Security of very simple XOR with random? [duplicate]

I am currently trying to implement a very fast and simple encryption algorithm in Lua for the purpose of using it with ComputerCraft. The main problem is that bitwise operations in Lua (5.2 at least) ...
4
votes
2answers
137 views

Are variable-length crypto hash functions still susceptible to collisions?

I just recently learned that the SHA-3 finalist Keccak allows for variable length output. As the only answer to this question states, "[it] need to have an output length at least equal to the input ...
4
votes
1answer
160 views

Is hashing a list of hashes safe?

I have an arbitrary long list of hashes (e.g. git tree hashes), and I'm wondering by how much I am increasing the risk of hash collisions by condensing them into a single hash, like so: ...
3
votes
1answer
164 views

PBKDF2 Salt and Password Ordering

I am currently reading about PBKDF2, and understand that the salt is used only once, while the password is used multiple times in the computation of the final key (see this question). How would the ...
3
votes
1answer
277 views

Possible CPA or CCA attack when using AES-CBC mode under the following situation?

Both client and server know a shared key in advance. Both sides us EVP_BytesToKey() derive a pair of same key and same IV. Then, client and server start transferring data encrypted by AES-CBC mode ...
1
vote
1answer
286 views

What's the point of a Meet In The Middle attack using i.e. double AES with throw-away keys?

What's the point of a Meet In The Middle attack while using, for example, a double AES encryption and using one time keys? You can recover the keys for a secret message already known and you can't use ...
3
votes
1answer
126 views

Partial hash code protocol for security tokens providing signatures

I've read the following two sentences within a beta protocol specification, which references ISO/IEC 7816-8 for PSO:HASH which already contains notions of a "partial hash". The off-card entity is ...
1
vote
1answer
129 views

Comparing Difference Distribution Tables

I have been studying the Diff. Cryptanalysis and finding it hard to do a problem. The problem is I have calculated the tables programmatically and found that the second table has a max value of 6 ...
2
votes
1answer
162 views

PBKDF2-SHA256+SHA256 for password storage

I recently came across an interesting paper detailing the use of hardened session cookies. Each cookie includes a preimage of the password hash, and the preimage is hashed once more and compared to ...

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