Secret Key Vs. Public Key
The secret method uses the same key to encrypt and decrypt. The problem is transmitting the key to the recipient in order to use it. The public key method uses two keys: one kept private and never transmitted, while the other is made public. Very often, the public key method is used to safely send the secret key to the recipient so that the message can be encrypted using the faster secret key algorithm.
Some Public History About Secret Methods The following is reprinted with permission from RSA Security, Inc. In 1518, a Benedictine monk named Johannes Trithemius wrote "Polygraphiae," the first published treatise on cryptography. Later, his text "Steganographia" described a cipher in which each letter is represented by words in successive columns of text, designed to hide inconspicuously inside a seemingly pious book of prayer. Polygraphiae and Steganographia attracted a considerable amount of attention not only for their meticulous analysis of ciphers but more notable for the unexpected thesis of Steganographia's third and final section, which claimed that messages communicated secretly were aided in their transmission by a host of summoned spirits. As might be expected, Trithemius' works were widely renounced as having magical content - by no means an unfamiliar theme in cryptographic history - and a century later fell victim to the zealous flames of the Inquisition during which they were banned as heretical sorcery.
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