The Free On-line Dictionary of Computing (30 December 2018):

private-key cryptography

    As opposed to public-key cryptography, a
   cryptographic method in which the same key is used to encrypt
   and decrypt the message.  Private-key algorithms include the
   obsolescent Data Encryption Standard (DES), triple-DES
   (3DES), the Advanced Encryption Standard (AES), also known
   as Rijndael, Blowfish, Twofish RC2, RC4, RC5 and RC6.

   A problem with private-key cryptography is that the sender and
   the recipient of the message must agree on a common key via
   some alternative secure channel.

   Public-key cryptography gives an answer to this problem.

   (2008-02-07)