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 emitter and the recipient of the message must agree secretly on a common key beforehands but how can they do so? Public-key cryptography gives an answer to this problem. (2003-04-12)