# Tag Info

14

These are completely different things: Man-in-the-middle is an active attack to a cryptographic protocol, where the attacker is, effectively, in between the communications of two users, and is capable of intercepting, relying, and (possibly) altering messages. In this case, the meaning of "in the middle" is direct: the attacker is in the middle of two ...

3

Any shared secret can be used. Securely distributed passwords and symmetric keys, for example. Alternatively, you can use asymmetric cryptography, such as public keys. For one example, SSH has for years authenticated servers using public key cryptography and users typically using either public keys or passwords. Only recently had SSH added support for ...

3

However, Eve has a copy of Alice's key pair and intercepted the outgoing message. She uses crypto_box_open and passes in pKb and sKa, the same keys that were used to encrypt the message. This yields the plain text message. She changes the message, re-encrypts it, and sends it on to Bob. As you correctly observed, Eve having Alice's private key is ...

2

What you observed here is a "special" and "unusual" behavior of the NaCl interface in the way it handles the crypto_box. What the crypto_box does is basically perform a static Diffie-Hellman key-exchange (using your secret and the recipient's public key) between you and the receiver and derive keys from that. So you get the same symmetric encryption key for ...

2

The reason Lamport's scheme is secure against a passive attacker is that even if they see $H^{n-1}(p)$ for a given $n$, the server would require the preimage of that hash, $H^{n-2}(p)$ on the next login. The active attack, in comparison, allows Trudy to find an earlier iteration than the server is expecting. That allows calculating several login hashes by ...

2

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 ...

1

Simply put, there are two key-pairs for DHE_RSA instead one key-pair of RSA_RSA. For example, for AES128_CBC_SHA(long name is RSA_RSA_AES128_CBC_SHA), you have one key-pair for both key-exchange and authentication. for ECDHE_RSA_AES_CBC_SHA, you have two key-pairs. The ECC key-pair is temporary for key-exchange. The RSA key-pair from cert is used for ...

1

When I sign a message (which has potentialy low entropy) using a private key and i send it without the original message, can the original message be retrieved from the Signaturen? It depends. If you use a signature scheme with appendix it will be impossible to recover the message using other ways than brute-force (so the answer would be "yes" for ...

1

TLSv1.1 doesn't have a different treatment of the key-exchange parameters than TLSv1.2 has. It's just a little less obvious. Let's dig into TLSv1.1 specification. On page 44 you'll find that ServerKeyExchange consists of ServerXXXParams params and Signature signed_params. Now on page 44 you'll actually find a definition of Signature. This definition signs ...

1

Suppose the server does not check the Client Finished value. This means that the MITM could change some handshake messages and the server would not know this (e.g., downgrade, as you mentioned). So, you could use this to fool a server that doesn't check the Client Finished value. If n bits are checked by the server, you have a 1/2^n chance of getting ...

1

Saying that ECDH does not do authentication is not entirely accurate. If you use ECDH with static, known public keys and both sides prove knowledge of the shared secret, then you do get authentication. However, with ephemeral keys you need some way to authenticate the exchange of public keys. That could be ECDSA or it could be any other authentication. So ...

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