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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, ...

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I would think these numbers would have been put on the google search engine, and yield (probably) many hits. This assumption is wrong. Certificate serial numbers are not indexed by common search engines, nor are they typically posted to any HTML site. Frankly, I'm not sure why you would assume they'd be indexed. The Wordpress certificate is used for ...

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You should keep the private key as safe as possible. How safe depends on the security requirements and risk assessment. A key store, such as a PKCS#12 key store or Java key store enables you to store a key protected by - usually - a password. This is obviously more secure than storing it as plaintext at the same location. It is possible to mitigate the risk ...

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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 ...

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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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In short: The parent CA would sign the public key of an n-time signature scheme, as opposed to the public key of a signature scheme which is valid for an unbounded number of signatures (the current design). n-time signature schemes are usually just constructed by generating n instances of a one-time signature scheme and then accumulating their public keys ...

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Great question. I'll answer it in several parts. Which Keys does Alice send? There are two cryptographic operations that Alice may want to do: encryption/decryption, and signing/validation. You can either use the same keypair for both, or have two separate pairs of keys. 1 keypair method: Here Alice would sign outgoing messages, and decrypt incoming ...

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Alice sends a CSR (certificate signing request) to the CA, which contains her public key, her name and usually her location. This CSR is then signed to prove ownership of the associated private key. The CA uses the data in the CSR to derive a certificate which will be handed to the user afterwards. The user can then prove his identity. The CA needs to ...

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This only works if you are absolutely certain that you're properly erasing the old private keys. This is harder than it seems; you have to be sure that you're leaving no traces anywhere, including on backup media or scattered around your hard drive. With proper forward secrecy methods, the keys never leave RAM, which makes erasing them securely much, much ...

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That scheme is effectively the same as having the parent CA counter-sign all issued certificates, since the parent will have to make a new signature (on a new accumulator) for each newly issued certificate. What are the features you want from such a scheme? To frame the question, here's a trivial scheme: client sends certificate request to child "CA"; ...

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This is a very interesting question, in the sense that every smart card provider claims the inviolability of its own process. Nowadays, Smart cards can generate their cryptographic keys on the card itself using appropriate hardware. Entropy is generally generated by an embedded random generator. The hardware of the generator is generally certified by ...

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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 ...

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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 ...

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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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