Background

Traditionally, cryptography has been used to pass coded messages between parties to ensure communication secrecy. Cryptography systems have used processes, techniques, and mechanisms to provide for secure communications between authorized parties while preventing unauthorized parties from monitoring communications or counterfeiting messages.

In its simplest form, cryptography substitutes or transposes letters to create a coded message, traditionally called a cipher, which is used to transform a readable message called plaintext (also called cleartext) into an unreadable, scrambled, or hidden message called ciphertext. Only someone with a decoding key can convert the ciphertext back into its original plaintext. The originator of a coded message must share the decoding key in a secure manner with intended recipients who are authorized to know the contents of the coded message. If unauthorized parties can somehow intercept or figure out the decoding key, security is compromised because they can convert the ciphertext into plaintext and read the contents of the message.

Anyone who can intercept both the ciphertext of a coded message and the decoding key can read secret communications. Furthermore, anyone who knows the cipher and has the decoding key might be able to impersonate the originator and send false messages. Therefore, systems of cryptography must provide reliable methods for securely sharing decoding keys, while keeping them unavailable to unauthorized parties. Others might know the cipher used to code a message and might have access to the coded message, but only authorized recipients are able to decode the contents of the message with the shared decoding key. Systems of cryptography also include techniques and mechanisms for verifying that originators of coded messages are authentic as well as ways to ensure that messages have not been altered en route.

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