Direct Key Agreement Mode

When executing an ECDH key agreement between a static private key and a non-trustworthy public key, care should be taken to ensure that the public key is a valid point on the same curve as the private key. Otherwise, the static private key may be compromised. For NIST P-256, P-384 and P-521 curves, the appropriate validation routines are given in point 5.6.2.3.3 of [NIST.800-56A]. Information about the curves used by X25519 and X448 can be found in the security considerations of [RFC7748]. IANA can only accept registration updates from designated experts and should forward all applications for registration to the review mailing list. In Appendix C (example ECDH-ES Key Agreement Computation), you will find an example of how to calculate the key agreement with this method. The order of the curve is a really large number, so an attacker can`t do much with this curve (if the ecdh software is properly implemented) to guess the private key used in the agreement. This brings us to the following section: in this example, the ECDH-ES Key Agreement and KDF concat are used to deduce the content encryption key (CEK) as described in point 4.6 (Key Agreement with Elliptic Curve Curve Diffie-Hellman Ephemeral Static (ECDH-ES). In this example, ecdh-es Direct Key Agreement (ECDH-ES) mode is used to create an agreed key for AES GCM with a 128-bit key (enc value A128GCM). Complete the Diffie Hellman key exchange process as a local mechanism in accordance with JWA (RFC 7518) in Direct Key Agreement mode with the P-256, dT, and QC curves, to create a pair of CEKs (one for each direction) identified by the transaction ID.

The parametric values supported in this version of the specification are as follows: The following parameter values “alg” (algorithm) are used to indicate that the encrypted key JWE is the result of the encryption of the CEK with the result of the key agreement algorithm as the encryption key for the corresponding key change algorithm: this is just one of the many possibilities offered by JWE. A separate specification called RFC 7518 aka JSON Web Algorithms (JWA) lists all kinds of available algorithms that can be used. What we`re discussing today is the key agreement with Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES). This algorithm makes it possible to deduce an ephemeral shared secret (this blog post by Neil Madden shows a concrete example of how to make an ephemeral key agreement). This document describes the ECDH-1PU encryption algorithm for JWE, which is authenticated with public keys. The algorithm is similar to the existing ECDH-ES encryption algorithm, but adds an additional ECDH key agreement between the sender`s static keys and the recipient. This additional step allows the recipient to ensure the authenticity of the sender without requiring a structure of nested and then encrypted signed messages. The mode is also a useful element for creating interactive handshake protocols on JOSE. To show how the attack would work in practice, I set up a live protest in Heroku. In obscure-everglades-31759.herokuapp.com/ run a node application.js server that, in this case, acts as a victim.

The assumption is as follows: To be able to communicate with this web application, you must encrypt a token with the Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES). The static server public key required for the key agreement can be found in obscure-everglades-31759.herokuapp.com/ecdh-es-public.json: this section defines the characteristics of the key agreement with Elliptic Curve Diffie-Hellman Ephemeral Static [RFC6090] (McGrew, D., Igoe, K., and M. Salter, “Fundamental Elliptic Curve Cryptography Algorithms”, In combination with the KDF Concat, as defined in section 5.8.1 of [NIST.800-56A] (National Institute of Standards and Technology (NIST), “Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Crypty”, May 2013. . . .