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in diffie-hellman key exchange algorithm vulnerability's is good defined by RSA lab : "The Diffie-Hellman key exchange is vulnerable to a man-in-the-middle attack. In this attack, an opponent Carol intercepts Alice's public value and sends her own public value to Bob. When Bob transmits his public value, Carol substitutes it with her own and sends it to ...


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Depending on resources available on nodes and whether you are going to implement anything yourself, racoon and ipsec could be a solution. It supports nodes with x.509 certificates issued by a local CA. Please note this question is not simple at all.


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Key exchange is notoriously hard to get right, and I strongly recommend not to do your own (unless your security requirements are really minimal). For example, what you propose does not provide forward security, which is generally considered of great importance in key exchange protocols. The good news is that there is a paper doing exactly what you need; ...


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To start things: Don't roll your own crypto. What you're proposing is using standard static Diffie-Hellman for key-exchange, which by itself is a bad idea, as it will always result in the same key for each communcication between Alice and Bob. The key by itself should be safe, but as soon as it's broken all messages are as well. So if either the sender's ...


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Curve25519 was supposed to be mainly used for Diffie-Hellman key-exchange and it provides ~128bit security and should fulfill all standard security assumptions on elliptic curves (and even some more). Now to answer the question is: yes. ElGamal can be used securely with Curve25519, as ElGamal is simply a Diffie-Hellman key-exchange ($\delta= m*g^{\alpha ...


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I think you overlooked some words in section 9: Key re-exchange is performed using whatever encryption was in effect when the exchange was started. Encryption, compression, and MAC methods are not changed before a new SSH_MSG_NEWKEYS is sent after the key exchange (as in the initial key exchange). Note that it is better to keep to the ...


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If the order of $a=-1\mod{p}$ and $b=a^{e}\mod{p}$, then $b=\pm{1}\mod{p}$. If $b=1\mod{p}$, the discrete logarithm is $0$. If $b=-1\mod{p}$, the discrete logarithm is $1$.


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This is basically the difference between e.g. the RSA_ ciphersuites and the DHE_/ECDHE_ ciphersuites in the TLS protocols. Currently the standardization moves towards ECDHE_ because it provides forward secrecy: even if you factor the RSA key you can still not decrypt previous transmissions. Note that you don't have to MAC the session key before encryption ...


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The inventors of the Supersingular Isogeny Key Exchange, Defeo, Jao and Plut have posted some code on GITHUB at: https://github.com/defeo/ss-isogeny-software/ There is also a paper on implementation of this key exchange by some people from the University of Waterloo. Their paper is "Efficient Implementations of A Quantum-Resistant Key-Exchange Protocol on ...


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The answer is yes; see Chapter 21 of Galbraith's book. Suppose we have your Fixed-Inverse-DH oracle $O(\cdot)$, and given $g^a$ and $g^b$ we want to find $g^{ab}$. We do this in two steps. First, we use $O$ to compute $g^{a^2}$ from $g^{a}$—this is a related problem called the Square-DH problem. Then we use the quarter-squares identity to compute $g^{ab}$. ...


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Yes, you can use a (semi) static key pair for (Elliptic Curve) Diffie-Hellman. If you want to check for sure that you use ECDH correctly take a look at the NIST SP 56A which shows the various way that key agreement can be used. In this case you'd probably look for 6.2.2.2. Note that you should check the public keys for validity. Furthermore, this ...



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