0
votes
1answer
41 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...
1
vote
2answers
36 views

Does CTR mode yield a PRF?

Can the keystream generated by CTR mode be considered a pseudo-random function? I give more information. Assume $f$ is a PRF. We define a function which takes 2 inputs, the desired length, and an ...
1
vote
0answers
29 views

Key Size for Symmetric Homomorphic Encryption Over the Integers

In the paper Fully Homomorphic Encryption over the Integers, it mentions a symmetric key scheme on page 1 and 2. Key Generation: Pick a random odd number $p \epsilon [2^{N-1},2^N)$ Encrypt A Bit m: ...
1
vote
0answers
15 views

Is there a practical security difference between OTP with letters and OTP with numbers?

Is there a practical security difference between OTP with letters and OTP with numbers? If, for instance, I encrypt a letter message, using Tabula Recta, with a random letter key THISI SATES TXAAA - ...
2
votes
1answer
23 views

Requirements for the modulus in the Massey-Omura three pass protocol

In the Massey-Omura three pass protocol: How many bits long should the prime modulus $M$ be in order to be secure? Should the $M$ be secret? Should the $M$ be generated every time or it could be ...
1
vote
0answers
46 views

Proving an encrypted message contains (but does not 100% consist of) a plain-text message?

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then concatenate X and Y, into Z. I encrypt Z, into "encrypt(Z,u) = Q". r is ...
1
vote
0answers
17 views

Concepts for realization in applied cryptography

I'm a computer science student (not a mathematican) and I'm gonna to write a master degree diploma on applied cryptography. Specifically, I'd like to create a realization of some cryptographic stuff ...
2
votes
2answers
610 views

Generate RSA-2048 private key for a VERY fast decryption (don't care if it will be unsecure)

Given public standard RSA exponent e = 65537, is there any (d, n) pairs so that RSA decryption becomes a trivial operation? The modulus n must be no less than 2048-bit. The goal is to get a real ...
1
vote
0answers
17 views

Where is CFB-MAC defined?

I can find a couple of descriptions of using CFB mode to create a MAC, but cannot find any standard or papers analyzing its security bounds. Is there a standard for CFB-MAC? Where can I find an ...
3
votes
2answers
170 views

Is Curve25519 vulnerable to private key exposure in the case of a bad RNG?

I'm really excited by what I've learned of advancements in elliptic-curve cryptography. Curve25519 seems to be a great choice at this point in time, but if I recall correctly, some elliptic curve ...
2
votes
1answer
18 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
3
votes
2answers
46 views

A periodic PRNG based on hash function?

I need a PRNG which provides 128 bytes numbers. Let's say that given a symmetric key $K$ and an internal state $s$ I use the PRF HMAC-SHA512 this way: The output is PRNG($K, s$) = ...
2
votes
1answer
525 views

Are there ANY text strings that will generate the same SHA-512 Hash output? [duplicate]

Are there ANY text strings that will generate the same SHA-512 Hash output? Please provide an example, and how you came to that conclusion. I've tried thousands of variations, including ".." vs. "." ...
3
votes
2answers
190 views

PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
1
vote
0answers
17 views

Proving an encrypted message contains (but does not 100% consist of) a plain-text message? [duplicate]

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then combine X and Y, into c(X,Y) = Z. I encrypt Z, into "encrypt(Z,u) = Q". r ...
1
vote
1answer
62 views

Formula for the number of expected collisions

Say we have a hash function that produces $n$ bit outputs. From the birthday problem that after around $\sqrt{2^n}$ different inputs to the has function, we can expect a collision. Say instead that ...
0
votes
2answers
76 views

DES hardware implementation of substitution lookup table [ ReWorked ]

I'm a crypto enthusiastic and student of cryptography. I'm developing a project with other students titled "A hardware implementation of a DES cryptography for educational purposes", our idea was to ...
3
votes
1answer
60 views

Why do we truncate the hash when using DSA?

All the articles I read on the web about DSA keep telling me that the size of the hash needs to be truncated so that the bit length is equal to or lesser than the bit length of the prime number of the ...
3
votes
0answers
24 views

Size of encrypted AES CEK in CMS block

When I run openssl cms -encrypt -aes256 -in sample.der -out wrapped.der -outform DER -recip ecc.crt -keyopt ecdh_kdf_md:sha512 the part of the CMS output which ...
2
votes
1answer
76 views

Calculating $\mathbb F_{p^2}$-rational points of an elliptic curve defined over $\mathbb F_p$

How can I calculate points on an elliptic curve defined over $\mathbb F_p$, for example $y^2 \equiv x^3 + 1 \pmod p$, with coordinates in $\mathbb F_{p^2}$? (points might have complex number format in ...
1
vote
0answers
12 views

Is there any equivalent to the apache xml security library for JSON? [on hold]

I'm talking about org.apache.xml.security(santurio) Is there any equivalent library that works with JSON and provides the same set of features? (mostly AES-128 with KEK support)
2
votes
2answers
37 views

Privacy and Integrity in Public Cryptography

I'm trying to figure out which is the best way to get privacy and integrity together in public cryptography. Alice needs to send multiple files $f$ (may be big) to Bob. I've thought: Alice computes ...
4
votes
1answer
130 views

Are ideal hashes possible to create?

In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve). Hence, isn't it ...
25
votes
2answers
1k views

What security authorities and standards reject $e=3$ in RSA, when, and with what rationale?

In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following: PKCS#1 allows ...
0
votes
0answers
21 views

In DGHV FHE, why noise $r$ can be in $(-2^{\rho'}, 0)$?

"Fully Homomorphic Encryption over the Integer" described a simple FHE scheme based on the GACD assumption. Its encryption function (on page 6) has the form $c \leftarrow (m + 2r + 2*\sum_{i \in S} ...
2
votes
1answer
24 views

RSA - PKCS#1 padding - overall correction of algorithm

From PKCS#1, page 24: After we create the EM byte string and convert it to an integer, we then encrypt that integer with RSAEP (page 10) to get the ciphertext (as an integer). My question arrives ...
5
votes
3answers
360 views

Stateless hash based public key cryptography?

Merkle-Winternitz signatures based on fractal hash trees are an attractive alternative to other post-quantum cryptographic schemes, in particular since they are conceptually simple, the security ...
2
votes
1answer
125 views

In HMQV, can one use multiple identities with one public key?

The HMQV protocol has 2 "identity" fields $\hat{A}, \hat{B}$ that are used in the dual signature - and it tries to guarantee that any properly-generated session key is only shared by a single $(A, B, ...
0
votes
0answers
40 views

Are there any cryptosystems that use multiple keys to perform encryption instead of one or two? [on hold]

Are there any cryptosystem that uses multiple keys (3 or more) to perform encryption rather than one (symmetric-key cryptography) or two (RSA, public-key cryptography, etc)?
1
vote
1answer
52 views

Ensuring integrity and confidentiality together with symmetric encryption

I've been required to answer a question: As usually, we have Alice and Bob. Suppose Alice wants to send a file F to Bob, ensuring integrity and confidentiality. They share a symmetryc key ...
1
vote
1answer
26 views

One time pad- XORing or substitution

I have come across 2 versions of otp while reading it and want to confirm it. they have taken a plain text consisting of alphabets where they are shifted and replaced by alphabets itself. XORing of ...
1
vote
0answers
28 views

CPA-security proof of “l-padded RSA” encryption scheme

The 10.9 exercise from the Katz-Lindell textbook creates a lot of confusion, let me state it here. Consider the following experiment for an algorithm $A$ and a function $l$ with $l(n) \leq 2n-2$ for ...
2
votes
1answer
35 views

Hitting a counter example in homomorphic encryption over the integers

The paper Fully Homomorphic Encryption over the Integers talks about a super simple symmetric key implementation on page 1 and 2. It says that to generate a key, you pick a random odd number between ...
7
votes
1answer
303 views

Does Curve25519 only provide 112 bit security?

In a recent mail on the IETF CFRG mailing list it was claimed that: The (currently missing) security considerations (or somewhere) should describe why Curve25519 is ok when used in contexts where ...
2
votes
1answer
18 views

Exchanging keys via third party

In many symmetric key ciphers sender and receiver have to exchange a single key. They may also do it through 3rd party who distributes it to both of them. since 3rd party can read all messages ...
3
votes
2answers
62 views

Randomness in Public Key Encryption

For a scheme to be at least CPA secure, one has to randomize the scheme. In case of a secret key encryption scheme, the used randomness will typically become part of the cipher text as in the case of ...
4
votes
1answer
205 views

Can iterated hashing be used to mitigate collision and preimage weaknesses?

How much security does double hashing add regarding collisions and preimages? Is it helpful to iterate a hash function even more times than two? For example, can MD5 be fixed (in practice) by ...
1
vote
0answers
9 views

Encipher the following plaintext message using the Vignere method using the key K = [4,2,3] [on hold]

Encipher the following plaintext message, Exotic, using the Vignere method using the key K = [4,2,3] Can anyone help me get the ...
4
votes
4answers
492 views

Is there a way to generate sound one-time pads out of public information?

Is there a way to 'mangle' a public data-source (for example, the current date in YYYYMMDD or the top New York Times headline) to form a one-time pad that will sufficiently hide the pad's source? ...
5
votes
1answer
86 views

What was the NSA's reasoning for making their bitwise combination functions in SHA-1 the way they did?

I know that these functions are there to actually make the program work. What I want to know is why they made the functions one way but not another. For example, why did they pick F1(B, C, D) = (B ...
3
votes
4answers
126 views

Cryptography and FPGA

I see a lot of papers about FPGA implementations. For what kind of "concrete" application should we implement cryptographic algorithms on FPGA ? Which secured application require such a huge data ...
1
vote
1answer
22 views

Clarification of RFC2246 with regards to Finished Message

I'm working on a client handshake finished message for a TLS client, and I'm reading through the RFC 2246 spec. The spec states (in section 7.4.9): The hash contained in finished messages sent by ...
9
votes
6answers
395 views

Choose a random number that is different from a bunch of other secret numbers

I'm looking for an algorithm where n participants each have a different secret number between $[0..x]$ (and where $x$ is known) and where the participants then select randomly another, non-secret, ...
-2
votes
1answer
55 views

Having plaintext and ciphertext, how can I learn more about key/encryption?

I have an OLD work database that seems to have a simple encryption on the PW. I have one users whose pw is 7777 the cipher text is ...
2
votes
1answer
36 views

Symmetric key in homomorphic encryption over the integers

Much like this question: Public key in fully homomorphic encryption over the integers I am also reading I'm reading Fully Homomorphic Encryption over the Integers, but I'm working on implementing the ...
2
votes
0answers
48 views

Proving set membership in less than log(N) bandwidth

I have an unchanging set of unique items, and I want my server to show one of those items to a client, then cryptographically prove that the item is part of the set. How I do this currently: ...
6
votes
3answers
153 views

What is stopping someone from saving encrypted info, and decoding it later?

When I send encrypted data to a website, using public key encryption, what is stopping someone who is listening from storing my encrypted data, and decryption it in a few years after they have ...
6
votes
1answer
57 views

Can RSA be securely used for “blind decryption”?

Assume we have the following setup: A client with trusted storage and computing capabilities (e.g. a smartcard) A server with trusted computing and short-term storage capabilities (e.g. RAM + CPU, ...
1
vote
0answers
47 views

Inverse public-key encryption

I'm in the need of an inverse public-key encryption method where you encrypt with the private key and decrypt with the public key. In other words an asymetric encryption where you can't generate the ...
4
votes
4answers
55 views

Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?

Imagine we have $t-1$ shares in $(t,n)$ shamir secret sharing. So at least $t$ shares are needed. Question: Why cannot we use $t-1$ shares to find a root of the polynomial and then recover the ...

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