The best replacement for public key is private key.

The best alternatives to public key are rated as following:
★★★★★  private key
★★★  certificate
★  secret key
★  symmetric encryption
★  public key token
  symmetric key
  asymmetric
  shared key

Your alternative for public key is not listed? Suggest!
Speaking about public key, one probably shouldn't forget about filezilla.

Other search terms related to public key and their ratings are:
★★★★★ filezilla
★★★★ sftp
★★★ ssh
gnupg
You have in mind a companion for public key and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of public key in all years. Click on graph for more.
public key
private key
certificate