The best replacement for pki is pgp.

The best alternatives to pki are rated as following:
★★★★★  pgp
★★★★  ssl
★★★★  kerberos
★★  in house
★★  ki
★  eca
★  psk
★  digital signature
★  symmetric key
★  pke
  web of trust
  non pki
  public key cryptography
  ibe

Your alternative for pki is not listed? Suggest!
Speaking about pki, one probably shouldn't forget about hsm.

Other search terms related to pki and their ratings are:
★★★★★ hsm
You have in mind a companion for pki and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of pki in all years. Click on graph for more.
pki
pgp
ssl