@misc{rfc4189,
    series =    {Request for Comments},
    number =    4189,
    howpublished =  {RFC 4189},
    publisher = {RFC Editor},
    doi =       {10.17487/RFC4189},
    url =       {https://www.rfc-editor.org/info/rfc4189},
    author =    {Kumiko Ono and Shinya Tachimoto},
    title =     {{Requirements for End-to-Middle Security for the Session Initiation Protocol (SIP)}},
    pagetotal = 12,
    year =      2005,
    month =     oct,
    abstract =  {A Session Initiation Protocol (SIP) User Agent (UA) does not always trust all intermediaries in its request path to inspect its message bodies and/or headers contained in its message. The UA might want to protect the message bodies and/or headers from intermediaries, except those that provide services based on its content. This situation requires a mechanism called "end-to-middle security" to secure the information passed between the UA and intermediaries, which does not interfere with end-to-end security. This document defines a set of requirements for a mechanism to achieve end-to-middle security. This memo provides information for the Internet community.},
}