%% You should probably cite draft-ietf-webpush-encryption instead of this I-D.
@techreport{thomson-webpush-encryption-01,
    number =    {draft-thomson-webpush-encryption-01},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-thomson-webpush-encryption/01/},
    author =    {Martin Thomson},
    title =     {{Message Encryption for Web Push}},
    pagetotal = 7,
    year =      2015,
    month =     jul,
    day =       2,
    abstract =  {A message encryption scheme is described for the Web Push protocol. This scheme provides confidentiality and integrity for messages sent from an Application Server to a User Agent.},
}