What does Boxing Day have to do with boxing?
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.