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8

Although x.509 is the standard for PKIs with CAs, different certificate formats have been defined for the other 2 major PKI approaches: SPKI has defined its own certificate format , still (forever?) in draft status. Web-of-Trust models usually use the OpenPGP certificate format defined in RFC2440 RFC4212 "Alternative Certificate Formats for the ...


5

You are looking for Proxy Re-Encryption. From a high-level viewpoint, a proxy re-encryption scheme is an asymmetric encryption scheme that permits a proxy to transform ciphertexts under Alice's public key into ciphertexts decryptable by Bob's secret key. In order to do this, the delegator $A$ gives a special re-encryption key $rk_{A \rightarrow B}$ to the ...


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Card verifiable certificates (CVC) are rather important for smart card technologies. In general X509 certificates have a rather complex structure and may take a lot of room compared to the RAM and EEPROM/flash memory that is available in a smart card chip. It is certainly possible to parse an X509 certificate in a processor card (it's a generic processor, ...


2

Firstly, PKI makes use of a private key and a public key. The private key is known only to the user, while the public key is communicated securely via the use of certificates. To provide authentication and non-repudiation, users may sign a message with their private keys and obtain a digital signature. Any other users can verify that the signed signature is ...


2

Quote from http://www.digi-sign.com/node/10922 All Types of Digital Certificates Are Also a X509 Certificate A X509 certificate *refers to all types of digital certificates, regardless of how they are utilized, and implies the current standardization used to design and create digital certificates. This standardization recognizes that the ...


2

Well, as it says in your link the problem is authentication. So somehow Alice and Bob must set up an authenticated channel. One way of implementing such a channel is by Alice and Bob holding each others public verification key for a signature scheme. A CA would probably not hold a secret key for Alice and Bob. However, using a CA to get an authentic copy ...


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The last 2 numbers are the ecdsa signature, it is two unsigned integers, when the highest byte happens to be larger than 127, the asn.1 BER encoding adds an extra zero.


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I think that this is not possible with a conventionnal public Key (Probably I'm wrong ?). But this question could easilly be solved by IBE as introduced by Dan Boneh in the seminal paper "Identity-Based Encryption from the Weil Pairing. This new system introduced in the early 2000, allows the Delegation of Decryption Keys, but this require the set up a new ...


1

The question Alex linked in comments explains why authentication works to prevent a man-in-the-middle attack on Diffie–Hellman. So, whenever you can do the key exchange in an authenticated channel, you can be sure there is no MitM attack. (Assuming DH problem remains unbroken, of course.) Now, your questions: Is one solution for both Alice and Bob ...


1

The problem about Man-in-the-Middle attack on Diffie-Hellman is that both sides are not confident about other side's public key (g^a and g^b). If they were sure that they have correct public key of their's friend Man-in-the-Middle attack wouldn't be possible, because MITM attack is based on the forgery of public keys by adversary! If for instance Bob and ...


1

I am a graduate student researching cryptography at JHU. If you want to research cryptography in academia, you'd better have a strong ability in mathematics. In my opinion, programming is a basic ability and software is just a kind of tool to realize your idea. cryptographers who made breakthroughs before all have a strong mathematics and theoretical ...



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