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Encrypted key exchange
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<p>Encrypted Key Exchange (also known as EKE) is a family of <a href="/facts/Password-authenticated_key_agreement/udf3tV4x">password-authenticated key agreement</a> methods described by <a href="/facts/Steven_M._Bellovin/m3gHMPN7">Steven M. Bellovin</a> and Michael Merritt. Although several of the forms of EKE in this paper were later found to be flawed , the surviving, refined, and enhanced forms of EKE effectively make this the first method to amplify a shared <a href="/facts/Password/WEoul230">password</a> into a shared key, where the <a href="/facts/Shared_key/5zfe0b76">shared key</a> may subsequently be used to provide a <a href="/facts/Zero-knowledge_password_proof/vgebecKq">zero-knowledge password proof</a> or other functions. </p><p>In the most general form of EKE, at least one party encrypts an ephemeral (one-time) public key using a password, and sends it to a second party, who decrypts it and uses it to negotiate a shared key with the first party. </p><p>A second paper describes Augmented-EKE, and introduced the concept of augmented <a href="/facts/Password-authenticated_key_agreement/udf3tV4x">password-authenticated key agreement</a> for client/server scenarios. Augmented methods have the added goal of ensuring that password verification data stolen from a server cannot be used by an attacker to masquerade as the client, unless the attacker first determines the password (e.g. by performing a brute force attack on the stolen data). </p><p>A version of EKE based on <a href="/facts/Diffie%E2%80%93Hellman_key_exchange/xR4YQcaD">Diffie–Hellman</a>, known as DH-EKE, has survived attack and has led to improved variations, such as the PAK family of methods in <a href="/facts/IEEE_P1363/pEjW4GjI">IEEE P1363.2</a>. </p><p>Since the <a href="/facts/US_patent/uxtfSzha">US patent</a> on EKE expired in late 2011, an <a href="/facts/Extensible_Authentication_Protocol/yuCAFHxC">EAP</a> authentication method using EKE was published as an IETF RFC. The EAP method uses the <a href="/facts/Diffie%E2%80%93Hellman_key_exchange/xR4YQcaD">Diffie–Hellman</a> variant of EKE. </p>