# Tag Info

9

I try to provide a brief intro. ABE Attribute-based encryption (ABE) is a relatively recent approach that reconsiders the concept of public-key cryptography. In traditional public-key cryptography, a message is encrypted for a specific receiver using the receiver’s public-key. Identity-based cryptography and in particular identity-based encryption (IBE) ...

5

Public key crypto vs. identity-based crypto made short: In traditional public key cryptography, a user $A$ generates a private/public key pair $(sk_A,pk_A)$ and since this key pair has absolutely no indication to which indentity (user $A$) it belongs, it is necessary to certify the public key, i.e., bind the public key $pk_A$ to the user $A$'s identity. ...

4

PE is a subclass of FE. This (from the other answer) is correct. Also, from my understanding, your analogy is correct. PE returns the plaintext if the predicate evaluates to true. FE, on the other hand, returns a function of the plaintext. We can say that PE is a subclass of FE, since we can use FE to implement PE. Just use the identity function. ...

4

She can generate a key-pair and include the public key in the book. Having the private counterpart she can at any time proove that she wrote the book by signing an arbitrary statament.

3

Zero-knowledge proofs of knowledge basically allow Alice to convince someone beyond a reasonable doubt that she knows a certain piece of information (i.e., the answer to a certain question), without revealing what exactly that information is. One simple example involves the discrete logarithm problem, which you might be familiar with: given a (large) prime ...

2

You can probably prove the security against your game from the security in the IND-ID-CCA game of Boneh and Franklin (see http://courses.cs.vt.edu/cs6204/Privacy-Security/Papers/Crypto/IBE-Weil-Pairing.pdf). The idea is to create an adversary $\mathcal{B}$ against IND-ID-CCA from your adversary $\mathcal{A}$. Essentially $\mathcal{B}$ will play ...

2

What you are describing is an anonymous credential system. There are two different ways to go about making these and two actual systems that use those techniques: Microsoft's U-prove and IBM's Idemix. If you're interested in smart card usage, you'd probably prefer U-prove as it tends to work better with smart cards. It's described by its original ...

2

If Bob and Charlie will share a secret, then it information-theoretic privacy might be possible, otherwise the best that can be hoped for is computational anonymity. I haven't come up up with any way to achieve information-theoretic privacy when Bob and Charlie share a secret, so I will only be addressing computational privacy. I assume that Bob can ...

2

There really isn't a difference. It is just author preference in notation. Some authors prefer to write the pairing operations multiplicatively $e(P^a, Q^b)=e(P,Q)^{ab}$ while others prefer to write it additively $e(aP,bQ)=e(P,Q)^{ab}$. This comes from the fact that in $e : \mathbb{G}_1\times \mathbb{G}_2\to\mathbb{G}_T$, $\mathbb{G}_1$ and $\mathbb{G}_2$ ...

2

Alice generates a signature key-pair and puts $\;$ the fact that she's using this identity-proving construction $\;\;\;\;$ and $\;$ the digital signature scheme $\;\;\;\;$ and $\;$ the prefix-free code $\;\;\;\;$ and $\;$ the verification key into the book, and keeps the signing key. (Let "||" denote concatenation.) For interactive verification, the ...

2

Compute $d$ such that $ed\equiv 1\bmod{\varphi(n)}$ using extended euclidean algorithm. Then compute $g = i^d\bmod{n}$. This is basically RSA decryption.

1

In these systems, is adversary able to generate semi-functional ciphertexts? Quoting the paper figlesquidge mentioned in a comment: Crypto 2009 Dual System Encryption: Realizing Fully Secure IBE and HIBE under Simple Assumptions Brent Waters Abstract: We present a new methodology for proving security of encryption systems using what we call ...

1

The problem that arises in the security proof is that the adversary who may win the real game with some probability may however cause the simulation to nearly always abort (by issuing a private key query that requires the simulation to abort) and the probability of an abort may be different for different sets of private key queries. So, the problem is that ...

1

Ok, lets look at the operations. Sign: $s = g * r^{f(t,m)} \pmod n$ This is an assignment. You compute $(g * r^{f(t,m)}) \mod n$ and assign the resulting value to $s$. If you have a multiplication $(a \cdot b) \mod n$, this is equal to $((a \mod n)\cdot (b \mod n)) \mod n$. See for instance here. Verification: $s^e = i * t^{f(t, m)} \pmod n$ This is no ...

1

PE is subclass of FE. For more description,see page number 256 of book, Theory of Cryptography: 8th Theory of Cryptography Conference, TCC 2011.

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